Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Richard (Rick) Karlquist]

Driscoll wrote a lot about oscillators over the years.
I couldn't find anything specific to discontinuous operation.
Do you have a titel of a paper related to this?


What Driscoll was talking about was self limiting in a
transistor.  That is discontinuous operation, although
Driscoll doesn't call it that.  His earliest papers on
this circuit go back to around 1972, and are in either
UFFC proceedings and/or FCS.  Many later papers cite
these.




The 2 transistor "Driscoll oscillator" fixes this problem
by using an additional stage that limits instead of the
oscillator transistor.


Is the Burgoon patent you are refering to US4283691
"Crystal oscillator having low noise signal extraction circuit" ?


Yes.

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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Attila Kinali]

Salut,

Thanks everyone for answering my questions and englighting me on
the general topic.

Sorry for the late answer from my side. It took me some time to
read up on all the pointers and hints provided. I'll quickly add
some  comments and questions to a few of the mails, that I find
noteworth, while i'm digging deeper into the topic.



On Tue, 27 Oct 2015 01:31:36 + (UTC)
Bruce Griffiths  wrote:

> http://ri.search.yahoo.com/_ylt=AwrTcaxMzS5WgJIAMwk3QIpQ;_ylu=X3oDMTBzbW1zYXBzBHNlYwNzcgRwb3MDMjEEY29sbwNncTEEdnRpZAM-/RV=2/RE=1445936589/RO=10/RU=https%3a%2f%2fescies.org%2fdownload%2fwebDocumentFile%3fid%3d60902/RK=0/RS=.Rmksavr9Ui3TZ8D1XyZ06TpeDY-


The correct URL here is https://escies.org/download/webDocumentFile?id=60902
and referencing to the document
"Low Noise Master Oscillator LNMO" by Wagner and Desaules.




On Mon, 26 Oct 2015 20:19:35 -0700
"Richard (Rick) Karlquist"  wrote:

> The oscillator transistor and buffer amplifier are basically
> the same as the HP 10811, except for the absence of mode
> suppressors.  The difference here is that the oscillator
> self limits in the oscillator transistor, whereas the 10811
> has ALC.  The discontinuous operation of the transistor,
> as explained by Driscoll some 45 years ago, is undesirable
> because it increases the load resistance the crystal sees.

Driscoll wrote a lot about oscillators over the years.
I couldn't find anything specific to discontinuous operation.
Do you have a titel of a paper related to this?


> The 2 transistor "Driscoll oscillator" fixes this problem
> by using an additional stage that limits instead of the
> oscillator transistor.

A good introduction to Driscolls oscillator design can be found in:

"Notes on the Driscoll VHF Overtone Crystal Oscillator and
New Low-Noise VHF Crystal Oscillator Topology" by Chris Bartram GW4DGU, 2008
page 5 in "Scatterpoint"
http://www.microwavers.org/scatterpoint/2008/Scatterpoint_Apr_2008.pdf


> I have demonstrated that the close in phase noise in
> the 10811 is entirely due to the flicker noise of the
> crystal.  The only place where the 10811 circuit comes
> into play is beyond 1 kHz from the carrier, where the
> Burgoon patent circuit (which apparently has prior art

Is the Burgoon patent you are refering to US4283691
"Crystal oscillator having low noise signal extraction circuit" ?





On Wed, 28 Oct 2015 06:45:54 -0700
"Richard (Rick) Karlquist"  wrote:

> Bruce has it exactly right.  At offset frequencies beyond 1 kHz,
> the source impedance for the grounded base is very high due to
> the crystal impedance being very high.  As Burgoon explains,
> this condition suppresses base recombination noise, and the
> only noise mechanism that is significant is the collector shot
> noise.  (To minimize shot noise, don't run more DC collector
> current than necessary).
> 
> I read Ulrich Rohde's 1977 article showing this circuit,
> before I started working at HP in 1979.  When I got to HP,

The article in question is either 

"Stable Crystal Oscillators", Ham Radio Magazine, June, 1975
or 
"Effects of Noise in Receiving System", Ham Radio Magazine, November 1977

Unfortunately, there doesn't seem to be an online source for the
Ham Radio Magazine. If anyone has a digital version of these
articles, I would appreciate a copy.


Attila Kinali



-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Will]

Hi ,

Ham Radio Magazine used to be available on archive.org but has been
removed.  73 Magazine is still available.

CD's of it are available (expensive).

I'll look later and see which issue it was.

Cheers,
Will

On 09/11/15 11:19, Attila Kinali wrote:
> Salut,
>
> Thanks everyone for answering my questions and englighting me on
> the general topic.
>
> Sorry for the late answer from my side. It took me some time to
> read up on all the pointers and hints provided. I'll quickly add
> some  comments and questions to a few of the mails, that I find
> noteworth, while i'm digging deeper into the topic.
>
>
>
> On Tue, 27 Oct 2015 01:31:36 + (UTC)
> Bruce Griffiths  wrote:
>
>> http://ri.search.yahoo.com/_ylt=AwrTcaxMzS5WgJIAMwk3QIpQ;_ylu=X3oDMTBzbW1zYXBzBHNlYwNzcgRwb3MDMjEEY29sbwNncTEEdnRpZAM-/RV=2/RE=1445936589/RO=10/RU=https%3a%2f%2fescies.org%2fdownload%2fwebDocumentFile%3fid%3d60902/RK=0/RS=.Rmksavr9Ui3TZ8D1XyZ06TpeDY-
>
> The correct URL here is https://escies.org/download/webDocumentFile?id=60902
> and referencing to the document
> "Low Noise Master Oscillator LNMO" by Wagner and Desaules.
>
>
>
>
> On Mon, 26 Oct 2015 20:19:35 -0700
> "Richard (Rick) Karlquist"  wrote:
>
>> The oscillator transistor and buffer amplifier are basically
>> the same as the HP 10811, except for the absence of mode
>> suppressors.  The difference here is that the oscillator
>> self limits in the oscillator transistor, whereas the 10811
>> has ALC.  The discontinuous operation of the transistor,
>> as explained by Driscoll some 45 years ago, is undesirable
>> because it increases the load resistance the crystal sees.
> Driscoll wrote a lot about oscillators over the years.
> I couldn't find anything specific to discontinuous operation.
> Do you have a titel of a paper related to this?
>
>
>> The 2 transistor "Driscoll oscillator" fixes this problem
>> by using an additional stage that limits instead of the
>> oscillator transistor.
> A good introduction to Driscolls oscillator design can be found in:
>
> "Notes on the Driscoll VHF Overtone Crystal Oscillator and
> New Low-Noise VHF Crystal Oscillator Topology" by Chris Bartram GW4DGU, 2008
> page 5 in "Scatterpoint"
> http://www.microwavers.org/scatterpoint/2008/Scatterpoint_Apr_2008.pdf
>
>
>> I have demonstrated that the close in phase noise in
>> the 10811 is entirely due to the flicker noise of the
>> crystal.  The only place where the 10811 circuit comes
>> into play is beyond 1 kHz from the carrier, where the
>> Burgoon patent circuit (which apparently has prior art
> Is the Burgoon patent you are refering to US4283691
> "Crystal oscillator having low noise signal extraction circuit" ?
>
>
>
>
>
> On Wed, 28 Oct 2015 06:45:54 -0700
> "Richard (Rick) Karlquist"  wrote:
>
>> Bruce has it exactly right.  At offset frequencies beyond 1 kHz,
>> the source impedance for the grounded base is very high due to
>> the crystal impedance being very high.  As Burgoon explains,
>> this condition suppresses base recombination noise, and the
>> only noise mechanism that is significant is the collector shot
>> noise.  (To minimize shot noise, don't run more DC collector
>> current than necessary).
>>
>> I read Ulrich Rohde's 1977 article showing this circuit,
>> before I started working at HP in 1979.  When I got to HP,
> The article in question is either 
>
> "Stable Crystal Oscillators", Ham Radio Magazine, June, 1975
> or 
> "Effects of Noise in Receiving System", Ham Radio Magazine, November 1977
>
> Unfortunately, there doesn't seem to be an online source for the
> Ham Radio Magazine. If anyone has a digital version of these
> articles, I would appreciate a copy.
>
>
>   Attila Kinali
>
>
>

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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bob Camp]

Hi

They do it pretty much the same way everybody else makes the same
sort of oscillators. Design, build,  tune / select, test, re-tune/ select, 
re-test.
The amount of test / tune depends enormously on what level of oscillator 
is being made. > 80% of the volume shipped gets relatively less effort than 
the other 20%.

Bob

> On Oct 28, 2015, at 6:24 PM, Alexander Pummer  wrote:
> 
> Hi Rick,
> any info on how Wenzel makes that low noise oscillators?
> 73
> KJ6UHN
> Alex
> 
> On 10/28/2015 3:04 PM, Richard (Rick) Karlquist wrote:
>> Do you have a specific URL for "hacking oscillators"?  I can't
>> find it on Rubiola's web site.
>> 
>> Rick
>> 
>> On 10/28/2015 1:32 PM, Gerhard Hoffmann wrote:
>>> Am 28.10.2015 um 19:22 schrieb KA2WEU--- via time-nuts:
 This oscillator seems to have been more a frequency standard then a noise
 standard. Today's 10 MHz oscillators are different/better, such a
 crystal is
 no  longer available/made.
>>> Yes. Rubiola gives it the credit of being able to be mass-produced, and
>>> it _was_
>>> one successful product. There is a section in "hacking oscillators" on it;
>>> my copy of the book is 200 miles away right now.
>>> 
>>> regards,
>>> 
>>> Gerhard, DK4XP
>>> 
>>> 
>>> (see www.rubiola.org)
>>> ___
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>> 
>> 
>> -
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2016.0.7163 / Virus Database: 4457/10906 - Release Date: 10/28/15
> 
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Jim Lux]

On 10/28/15 4:29 PM, Adrian wrote:

That's chapter 6 of his book.
http://rubiola.org/indexx-oscillator-noise.html
Just scroll down for the phase noise plots.
The left hand column of plots contains the essentials.

Adrian





what would be nice is some similar simple analysis for lower performing 
oscillators.. (like the oscillator in a PC, or run of the mill 1-10 ppm 
TCXOs)



tvb has some on his website.

I guess there's stuff around, but it's not all gathered together.


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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bruce Griffiths]

Ulrich

Surely you meant to write

PN(SSB) = -177 -Pout + NF

If we attempt to apply this equation to the 10811A for which you measured a PN 
floor of -174dBc/Hz
this implies that 

NF - Pout = 3dB

Best case (NF = 0dB - unlikely! Pout would need to be much higher for nonn zero 
NF)

Pout =-3dBm or 500uW.

The question is identifying this power.
The crystal dissipation is 50uW (HP Journal March 1981 p24)
The signal power dissipated in the CB stage input R is around 10% of this or 
about 5uW.

The answer to this conundrum is surely that the equation for PN doesn't apply 
directly in this case 
for offset frequencies outside the crystal bandwidth.
The Crystal actually bandpass filters the signal and PN noise generated by 
oscillator.
For offset frequencies outside the crystal bandwidth the oscillator generated 
PN is greatly attenuated 
so that the noise of the buffer amplifier chain (CB stage plus output 
amplifiers) dominates.
In calculating the noise floor of the buffer amplifier chain the fact that the 
crystal has 
a high impedance at these frequencies should be taken into account.     

Bruce 


 On Wednesday, 28 October 2015 8:34 AM, "ka2...@aol.com"  
wrote:
   

 I have bought and measured the hp10811 at about -174dBc/Hz. The interesting  
thing is  the feedback capacitor from collector to base which changes Rin=1/gm. 
Unless the circuit has a hidden Q mulitplier the PN (SSB) can never be better 
then 177 (kT) in dBm  + Pout  in dBm - NF of the oscillator transistor. Many of 
the GB stages are potentially unstable , so the "hopeful' best PN (SSB) is 
177dbm + Pout ! AT 100 Mhz the leaing values are -146/100Hz offset  and - 183 
far out and high crystal dissipation, 2mW or so  Ulrich  In a message dated 
10/27/2015 4:17:16 P.M. W. Europe Standard Time, bruce.griffi...@xtra.co.nz 
writes:
As Rick has pointed out numerous times when the output signal is extracted via 
the crystal by a CB stage (or cascade thereof) the PN floor is determined by 
the ratio of the amplifier equivalent input noise current to the crystal 
current. That is the amplifier equivalent input noise current at frequencies 
for which the crystal impedance is high. If one neglects this crucial point one 
comes to the conclusion (e.g. see Eq 4.-1 page 274 of Ulrich Rohde's: Microwave 
and Wireless Synthesisers Theory and Design.) that with a crystal current of 
1.4mA rms and a crystal esr of 50 ohms that the XO PN floor cannot be lower 
than -154dBc/Hz.  Even the XO circuit in the ARRL handbook (attributed to 
Ulrich) using this method of signal extraction has a measured PN floor of 
-168dBc/Hz.  Many other XO's (including the 10811A which uses a crystal current 
of 1mA ) have an actual PN significantly lower than this.  One would have 
thought that this glaring discrepancy between "theory" and practice would 
 have been noticed and corrected by now.
Bruce 


     On Tuesday, 27 October 2015 6:01 PM, Richard (Rick) Karlquist 
 wrote:
   

The oscillator transistor and buffer amplifier are basically
the same as the HP 10811, except for the absence of mode
suppressors.  The difference here is that the oscillator
self limits in the oscillator transistor, whereas the 10811
has ALC.  The discontinuous operation of the transistor,
as explained by Driscoll some 45 years ago, is undesirable
because it increases the load resistance the crystal sees.
The 2 transistor "Driscoll oscillator" fixes this problem
by using an additional stage that limits instead of the
oscillator transistor.  This has been widely used for
decades.  It is interesting to note that the 10811 ALC
works by varying the DC bias current in the oscillator
transistor.  This is in contrast to the elaborate DC
bias current stabilization here.

I have demonstrated that the close in phase noise in
the 10811 is entirely due to the flicker noise of the
crystal.  The only place where the 10811 circuit comes
into play is beyond 1 kHz from the carrier, where the
Burgoon patent circuit (which apparently has prior art
from Ulrich Rhode) reduces the phase noise floor.  I
have built two different oscillator circuits for 10811
crystals and have measured the flicker noise as being
the same as the intrinsic noise of the crystal.

Thus, obsessing over noise in oscillators circuits may
be overkill, unless you are planning to use a much
better crystal (BVA, etc).  OTOH, it might be advantageous
to improve the reverse isolation by adding additional
grounded base buffer stages.  There are various NBS/NIST
papers where several grounded base stages are cascaded.
I did this in the HP 10816 rubidium standard.

It is good to see time-nuts learning about oscillator
circuit by building them.

Rick Karlquist N6RK
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bruce Griffiths]

Ulrich
Whilst I do have an original somewhere, a pdf version can be found here:

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-03.pdf

Bruce
 


 On Wednesday, 28 October 2015 7:07 PM, Bruce Griffiths 
 wrote:
   

 Ulrich

Surely you meant to write

PN(SSB) = -177 -Pout + NF

If we attempt to apply this equation to the 10811A for which you measured a PN 
floor of -174dBc/Hz
this implies that 

NF - Pout = 3dB

Best case (NF = 0dB - unlikely! Pout would need to be much higher for nonn zero 
NF)

Pout =-3dBm or 500uW.

The question is identifying this power.
The crystal dissipation is 50uW (HP Journal March 1981 p24)
The signal power dissipated in the CB stage input R is around 10% of this or 
about 5uW.

The answer to this conundrum is surely that the equation for PN doesn't apply 
directly in this case 
for offset frequencies outside the crystal bandwidth.
The Crystal actually bandpass filters the signal and PN noise generated by 
oscillator.
For offset frequencies outside the crystal bandwidth the oscillator generated 
PN is greatly attenuated 
so that the noise of the buffer amplifier chain (CB stage plus output 
amplifiers) dominates.
In calculating the noise floor of the buffer amplifier chain the fact that the 
crystal has 
a high impedance at these frequencies should be taken into account.     

Bruce 


    On Wednesday, 28 October 2015 8:34 AM, "ka2...@aol.com"  
wrote:
  

 I have bought and measured the hp10811 at about -174dBc/Hz. The interesting  
thing is  the feedback capacitor from collector to base which changes Rin=1/gm. 
Unless the circuit has a hidden Q mulitplier the PN (SSB) can never be better 
then 177 (kT) in dBm  + Pout  in dBm - NF of the oscillator transistor. Many of 
the GB stages are potentially unstable , so the "hopeful' best PN (SSB) is 
177dbm + Pout ! AT 100 Mhz the leaing values are -146/100Hz offset  and - 183 
far out and high crystal dissipation, 2mW or so  Ulrich  In a message dated 
10/27/2015 4:17:16 P.M. W. Europe Standard Time, bruce.griffi...@xtra.co.nz 
writes:
As Rick has pointed out numerous times when the output signal is extracted via 
the crystal by a CB stage (or cascade thereof) the PN floor is determined by 
the ratio of the amplifier equivalent input noise current to the crystal 
current. That is the amplifier equivalent input noise current at frequencies 
for which the crystal impedance is high. If one neglects this crucial point one 
comes to the conclusion (e.g. see Eq 4.-1 page 274 of Ulrich Rohde's: Microwave 
and Wireless Synthesisers Theory and Design.) that with a crystal current of 
1.4mA rms and a crystal esr of 50 ohms that the XO PN floor cannot be lower 
than -154dBc/Hz.  Even the XO circuit in the ARRL handbook (attributed to 
Ulrich) using this method of signal extraction has a measured PN floor of 
-168dBc/Hz.  Many other XO's (including the 10811A which uses a crystal current 
of 1mA ) have an actual PN significantly lower than this.  One would have 
thought that this glaring discrepancy between "theory" and practice would 
 have been noticed and corrected by now.
Bruce 


     On Tuesday, 27 October 2015 6:01 PM, Richard (Rick) Karlquist 
 wrote:
   

The oscillator transistor and buffer amplifier are basically
the same as the HP 10811, except for the absence of mode
suppressors.  The difference here is that the oscillator
self limits in the oscillator transistor, whereas the 10811
has ALC.  The discontinuous operation of the transistor,
as explained by Driscoll some 45 years ago, is undesirable
because it increases the load resistance the crystal sees.
The 2 transistor "Driscoll oscillator" fixes this problem
by using an additional stage that limits instead of the
oscillator transistor.  This has been widely used for
decades.  It is interesting to note that the 10811 ALC
works by varying the DC bias current in the oscillator
transistor.  This is in contrast to the elaborate DC
bias current stabilization here.

I have demonstrated that the close in phase noise in
the 10811 is entirely due to the flicker noise of the
crystal.  The only place where the 10811 circuit comes
into play is beyond 1 kHz from the carrier, where the
Burgoon patent circuit (which apparently has prior art
from Ulrich Rhode) reduces the phase noise floor.  I
have built two different oscillator circuits for 10811
crystals and have measured the flicker noise as being
the same as the intrinsic noise of the crystal.

Thus, obsessing over noise in oscillators circuits may
be overkill, unless you are planning to use a much
better crystal (BVA, etc).  OTOH, it might be advantageous
to improve the reverse isolation by adding additional
grounded base buffer stages.  There are various NBS/NIST
papers where several grounded base stages are cascaded.
I did this in the HP 10816 rubidium standard.

It is good to see time-nuts learning about oscillator
circuit by building them.

Rick Karlquist N6RK

Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Richard (Rick) Karlquist]

On 10/27/2015 10:11 PM, Bruce Griffiths wrote:


The answer to this conundrum is surely that the equation for PN doesn't apply 
directly in this case
for offset frequencies outside the crystal bandwidth.
The Crystal actually bandpass filters the signal and PN noise generated by 
oscillator.
For offset frequencies outside the crystal bandwidth the oscillator generated 
PN is greatly attenuated
so that the noise of the buffer amplifier chain (CB stage plus output 
amplifiers) dominates.
In calculating the noise floor of the buffer amplifier chain the fact that the 
crystal has
a high impedance at these frequencies should be taken into account.

Bruce



Bruce has it exactly right.  At offset frequencies beyond 1 kHz,
the source impedance for the grounded base is very high due to
the crystal impedance being very high.  As Burgoon explains,
this condition suppresses base recombination noise, and the
only noise mechanism that is significant is the collector shot
noise.  (To minimize shot noise, don't run more DC collector
current than necessary).

I read Ulrich Rohde's 1977 article showing this circuit,
before I started working at HP in 1979.  When I got to HP,
and learned about the 10811, I pointed this article out to Burgoon.
It turns out he independently reinvented the circuit,
but he was apparently the first person to realize the noise implications
of the circuit.

This buffer circuit, extended to multiple grounded base stages
in cascade for additional reverse isolation, makes so much sense that
every oscillator where phase noise floor or reverse isolation
is important should be using it, IMHO.  (Burgoon's patent expired long
ago).

A brief comment about the collector-base capacitor in the 10811 Colpitts
circuit:  this has the usual Colpitts function at 10 MHz, but it
also prevents the 2N5179 from oscillating at 1 GHz.  It must be
installed very close to the transistor or else the 2N5179 will be
unstable.  I discovered this when I copied the schematic, but
not the layout, of the 10811 for use in the 10816 rubidium.

The 2N5179 in the 10811 is selected for minimum beta and Ft at
20 mA, which is the start up condition due to the ALC being
at full gain.  It has a special HP part number, so you wouldn't
know this just looking at the parts list.

Rick Karlquist N6RK
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Hal Murray]

rich...@karlquist.com said:
> The 2N5179 in the 10811 is selected for minimum beta and Ft at 20 mA, which
> is the start up condition due to the ALC being at full gain.  It has a
> special HP part number, so you wouldn't know this just looking at the parts
> list. 

How much of a difference does that selection step make?

I'd expect the parts within a batch to be very similar, more so for mature 
parts.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Magnus Danielson]

Hi,

It is well worth mentioning that a crystal filter on the output can 
become a challenge, as the source impedance can be far from 50 Ohm, and 
thus a bit of a challenge depending on how you measure.


Cheers,
Magnus

On 10/28/2015 06:11 AM, Bruce Griffiths wrote:

Ulrich

Surely you meant to write

PN(SSB) = -177 -Pout + NF

If we attempt to apply this equation to the 10811A for which you measured a PN 
floor of -174dBc/Hz
this implies that

NF - Pout = 3dB

Best case (NF = 0dB - unlikely! Pout would need to be much higher for nonn zero 
NF)

Pout =-3dBm or 500uW.

The question is identifying this power.
The crystal dissipation is 50uW (HP Journal March 1981 p24)
The signal power dissipated in the CB stage input R is around 10% of this or 
about 5uW.

The answer to this conundrum is surely that the equation for PN doesn't apply 
directly in this case
for offset frequencies outside the crystal bandwidth.
The Crystal actually bandpass filters the signal and PN noise generated by 
oscillator.
For offset frequencies outside the crystal bandwidth the oscillator generated 
PN is greatly attenuated
so that the noise of the buffer amplifier chain (CB stage plus output 
amplifiers) dominates.
In calculating the noise floor of the buffer amplifier chain the fact that the 
crystal has
a high impedance at these frequencies should be taken into account.

Bruce


  On Wednesday, 28 October 2015 8:34 AM, "ka2...@aol.com"  
wrote:


  I have bought and measured the hp10811 at about -174dBc/Hz. The interesting  thing 
is  the feedback capacitor from collector to base which changes Rin=1/gm. Unless the 
circuit has a hidden Q mulitplier the PN (SSB) can never be better then 177 (kT) in 
dBm  + Pout  in dBm - NF of the oscillator transistor. Many of the GB stages are 
potentially unstable , so the "hopeful' best PN (SSB) is 177dbm + Pout ! AT 100 
Mhz the leaing values are -146/100Hz offset  and - 183 far out and high crystal 
dissipation, 2mW or so  Ulrich  In a message dated 10/27/2015 4:17:16 P.M. W. Europe 
Standard Time, bruce.griffi...@xtra.co.nz writes:
As Rick has pointed out numerous times when the output signal is extracted via the 
crystal by a CB stage (or cascade thereof) the PN floor is determined by the ratio of the 
amplifier equivalent input noise current to the crystal current. That is the amplifier 
equivalent input noise current at frequencies for which the crystal impedance is high. If 
one neglects this crucial point one comes to the conclusion (e.g. see Eq 4.-1 page 274 of 
Ulrich Rohde's: Microwave and Wireless Synthesisers Theory and Design.) that with a 
crystal current of 1.4mA rms and a crystal esr of 50 ohms that the XO PN floor cannot be 
lower than -154dBc/Hz.  Even the XO circuit in the ARRL handbook (attributed to Ulrich) 
using this method of signal extraction has a measured PN floor of -168dBc/Hz.  Many other 
XO's (including the 10811A which uses a crystal current of 1mA ) have an actual PN 
significantly lower than this.  One would have thought that this glaring discrepancy 
between "theory" and practice would
  have been noticed and corrected by now.
Bruce


  On Tuesday, 27 October 2015 6:01 PM, Richard (Rick) Karlquist 
 wrote:


The oscillator transistor and buffer amplifier are basically
the same as the HP 10811, except for the absence of mode
suppressors.  The difference here is that the oscillator
self limits in the oscillator transistor, whereas the 10811
has ALC.  The discontinuous operation of the transistor,
as explained by Driscoll some 45 years ago, is undesirable
because it increases the load resistance the crystal sees.
The 2 transistor "Driscoll oscillator" fixes this problem
by using an additional stage that limits instead of the
oscillator transistor.  This has been widely used for
decades.  It is interesting to note that the 10811 ALC
works by varying the DC bias current in the oscillator
transistor.  This is in contrast to the elaborate DC
bias current stabilization here.

I have demonstrated that the close in phase noise in
the 10811 is entirely due to the flicker noise of the
crystal.  The only place where the 10811 circuit comes
into play is beyond 1 kHz from the carrier, where the
Burgoon patent circuit (which apparently has prior art
from Ulrich Rhode) reduces the phase noise floor.  I
have built two different oscillator circuits for 10811
crystals and have measured the flicker noise as being
the same as the intrinsic noise of the crystal.

Thus, obsessing over noise in oscillators circuits may
be overkill, unless you are planning to use a much
better crystal (BVA, etc).  OTOH, it might be advantageous
to improve the reverse isolation by adding additional
grounded base buffer stages.  There are various NBS/NIST
papers where several grounded base stages are cascaded.
I did this in the HP 10816 rubidium standard.

It is good to see time-nuts learning about oscillator
circuit by building them.

Rick Karlquist N6RK

Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[KA2WEU--- via time-nuts]

This oscillator seems to have been more a frequency standard then a noise  
standard. Today's 10 MHz oscillators are different/better, such a crystal is 
no  longer available/made.
 
I have more experience with 100 MHz, 125 and 128 MHz. Once I am back in the 
 USA  I will send some measured results and comments. 
 
Thank for this reference :
 
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-03.pdf
 
Ulrich 
 
 
In a message dated 10/28/2015 7:01:16 P.M. W. Europe Standard Time,  
hmur...@megapathdsl.net writes:


rich...@karlquist.com said:
> The 2N5179 in the 10811 is  selected for minimum beta and Ft at 20 mA, 
which
> is the start up  condition due to the ALC being at full gain.  It has a
> special HP  part number, so you wouldn't know this just looking at the 
parts
> list.  

How much of a difference does that selection step make?

I'd  expect the parts within a batch to be very similar, more so for mature 
 
parts.


-- 
These are my opinions.  I hate  spam.



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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Adrian]

That's chapter 6 of his book.
http://rubiola.org/indexx-oscillator-noise.html
Just scroll down for the phase noise plots.
The left hand column of plots contains the essentials.

Adrian



Richard (Rick) Karlquist schrieb:
> Do you have a specific URL for "hacking oscillators"?  I can't
> find it on Rubiola's web site.
>
> Rick
>
> On 10/28/2015 1:32 PM, Gerhard Hoffmann wrote:
>> Am 28.10.2015 um 19:22 schrieb KA2WEU--- via time-nuts:
>>> This oscillator seems to have been more a frequency standard then a
>>> noise
>>> standard. Today's 10 MHz oscillators are different/better, such a
>>> crystal is
>>> no  longer available/made.
>> Yes. Rubiola gives it the credit of being able to be mass-produced, and
>> it _was_
>> one successful product. There is a section in "hacking oscillators"
>> on it;
>> my copy of the book is 200 miles away right now.
>>
>> regards,
>>
>> Gerhard, DK4XP
>>
>>
>> (see www.rubiola.org)
>> ___
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Alexander Pummer]

Hi Rick,
any info on how Wenzel makes that low noise oscillators?
73
KJ6UHN
Alex

On 10/28/2015 3:04 PM, Richard (Rick) Karlquist wrote:

Do you have a specific URL for "hacking oscillators"?  I can't
find it on Rubiola's web site.

Rick

On 10/28/2015 1:32 PM, Gerhard Hoffmann wrote:

Am 28.10.2015 um 19:22 schrieb KA2WEU--- via time-nuts:
This oscillator seems to have been more a frequency standard then a 
noise

standard. Today's 10 MHz oscillators are different/better, such a
crystal is
no  longer available/made.

Yes. Rubiola gives it the credit of being able to be mass-produced, and
it _was_
one successful product. There is a section in "hacking oscillators" 
on it;

my copy of the book is 200 miles away right now.

regards,

Gerhard, DK4XP


(see www.rubiola.org)
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-
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10/28/15


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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[KA2WEU--- via time-nuts]

Yes, more the termination  Ulrich 
 
 
In a message dated 10/28/2015 9:02:56 P.M. W. Europe Standard Time,  
mag...@rubidium.dyndns.org writes:

Hi,

It is well worth mentioning that a crystal filter on the  output can 
become a challenge, as the source impedance can be far from 50  Ohm, and 
thus a bit of a challenge depending on how you  measure.

Cheers,
Magnus

On 10/28/2015 06:11 AM, Bruce  Griffiths wrote:
> Ulrich
>
> Surely you meant to  write
>
> PN(SSB) = -177 -Pout + NF
>
> If we attempt  to apply this equation to the 10811A for which you 
measured a PN floor of  -174dBc/Hz
> this implies that
>
> NF - Pout =  3dB
>
> Best case (NF = 0dB - unlikely! Pout would need to be much  higher for 
nonn zero NF)
>
> Pout =-3dBm or 500uW.
>
>  The question is identifying this power.
> The crystal dissipation is  50uW (HP Journal March 1981 p24)
> The signal power dissipated in the CB  stage input R is around 10% of 
this or about 5uW.
>
> The answer  to this conundrum is surely that the equation for PN doesn't 
apply directly in  this case
> for offset frequencies outside the crystal  bandwidth.
> The Crystal actually bandpass filters the signal and PN  noise generated 
by oscillator.
> For offset frequencies outside the  crystal bandwidth the oscillator 
generated PN is greatly attenuated
> so  that the noise of the buffer amplifier chain (CB stage plus output 
amplifiers)  dominates.
> In calculating the noise floor of the buffer amplifier  chain the fact 
that the crystal has
> a high impedance at these  frequencies should be taken into account.
>
>  Bruce
>
>
>   On Wednesday, 28  October 2015 8:34 AM, "ka2...@aol.com" 
  wrote:
>
>
>   I have bought and measured the  hp10811 at about -174dBc/Hz. The 
interesting  thing is  the feedback  capacitor from collector to base which 
changes Rin=1/gm. Unless the circuit  has a hidden Q mulitplier the PN (SSB) 
can 
never be better then 177 (kT) in  dBm  + Pout  in dBm - NF of the oscillator 
transistor. Many of the  GB stages are potentially unstable , so the 
"hopeful' best PN (SSB) is 177dbm  + Pout ! AT 100 Mhz the leaing values are 
-146/100Hz offset  and - 183  far out and high crystal dissipation, 2mW or so  
Ulrich  In a  message dated 10/27/2015 4:17:16 P.M. W. Europe Standard Time,  
bruce.griffi...@xtra.co.nz writes:
> As Rick has pointed out numerous  times when the output signal is 
extracted via the crystal by a CB stage (or  cascade thereof) the PN floor is 
determined by the ratio of the amplifier  equivalent input noise current to the 
crystal current. That is the amplifier  equivalent input noise current at 
frequencies for which the crystal impedance  is high. If one neglects this 
crucial point one comes to the conclusion (e.g.  see Eq 4.-1 page 274 of Ulrich 
Rohde's: Microwave and Wireless Synthesisers  Theory and Design.) that with 
a crystal current of 1.4mA rms and a crystal esr  of 50 ohms that the XO PN 
floor cannot be lower than -154dBc/Hz.  Even  the XO circuit in the ARRL 
handbook (attributed to Ulrich) using this method  of signal extraction has a 
measured PN floor of -168dBc/Hz.  Many other  XO's (including the 10811A 
which uses a crystal current of 1mA ) have an  actual PN significantly lower 
than this.  One would have thought that  this glaring discrepancy between 
"theory" and practice
would
>   have been noticed and corrected by now.
>  Bruce
>
>
>   On Tuesday, 27 October  2015 6:01 PM, Richard (Rick) Karlquist 
  wrote:
>
>
> The oscillator transistor and buffer amplifier  are basically
> the same as the HP 10811, except for the absence of  mode
> suppressors.  The difference here is that the  oscillator
> self limits in the oscillator transistor, whereas the  10811
> has ALC.  The discontinuous operation of the  transistor,
> as explained by Driscoll some 45 years ago, is  undesirable
> because it increases the load resistance the crystal  sees.
> The 2 transistor "Driscoll oscillator" fixes this  problem
> by using an additional stage that limits instead of  the
> oscillator transistor.  This has been widely used for
>  decades.  It is interesting to note that the 10811 ALC
> works by  varying the DC bias current in the oscillator
> transistor.  This  is in contrast to the elaborate DC
> bias current stabilization  here.
>
> I have demonstrated that the close in phase noise  in
> the 10811 is entirely due to the flicker noise of the
>  crystal.  The only place where the 10811 circuit comes
> into play  is beyond 1 kHz from the carrier, where the
> Burgoon patent circuit  (which apparently has prior art
> from Ulrich Rhode) reduces the phase  noise floor.  I
> have built two different oscillator circuits for  10811
> crystals and have measured the flicker noise as being
>  the same as the intrinsic noise of the crystal.
>
> Thus,  obsessing over noise in oscillators circuits may
> be overkill, unless  you are planning to use a much
> better crystal (BVA, etc).  

Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Gerhard Hoffmann]

Am 28.10.2015 um 19:22 schrieb KA2WEU--- via time-nuts:

This oscillator seems to have been more a frequency standard then a noise
standard. Today's 10 MHz oscillators are different/better, such a crystal is
no  longer available/made.
  
Yes. Rubiola gives it the credit of being able to be mass-produced, and 
it _was_

one successful product. There is a section in "hacking oscillators" on it;
my copy of the book is 200 miles away right now.

regards,

Gerhard, DK4XP


(see www.rubiola.org)
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Richard (Rick) Karlquist]

Do you have a specific URL for "hacking oscillators"?  I can't
find it on Rubiola's web site.

Rick

On 10/28/2015 1:32 PM, Gerhard Hoffmann wrote:

Am 28.10.2015 um 19:22 schrieb KA2WEU--- via time-nuts:

This oscillator seems to have been more a frequency standard then a noise
standard. Today's 10 MHz oscillators are different/better, such a
crystal is
no  longer available/made.

Yes. Rubiola gives it the credit of being able to be mass-produced, and
it _was_
one successful product. There is a section in "hacking oscillators" on it;
my copy of the book is 200 miles away right now.

regards,

Gerhard, DK4XP


(see www.rubiola.org)
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Richard (Rick) Karlquist]

On 10/28/2015 10:38 AM, Hal Murray wrote:


rich...@karlquist.com said:

The 2N5179 in the 10811 is selected for minimum beta and Ft at 20 mA, which
is the start up condition due to the ALC being at full gain.  It has a
special HP part number, so you wouldn't know this just looking at the parts
list.


How much of a difference does that selection step make?

I'd expect the parts within a batch to be very similar, more so for mature
parts.




All I can tell you is that Burgoon found a non-zero number of
2N5179's that wouldn't start. Knowing the way things were done,
he probably got a response from the vendor to the effect that
it was simply an unspecified parameter and they only guarantee
JEDEC specs and the transistor(s) he found were not a fluke.
HP greatly discouraged the batch qualification paradigm, although
the did resort to it when justified.  It was not justified for
the 10811.

Rick
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Mod Mix]

6 - Oscillator hacking  pp. 150-191  - 
http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511812798=CBO9780511812798A053

2 Oscillator hacking - http://arxiv.org/pdf/physics/0502143.pdf
A weird example; The effect of the output buffer; Oscillator hacking  - 
http://rubiola.org/pdf-slides/2009T-MPQ-Short-course-on-stable-oscillators.pdf


hth
Ulli

Am 28.10.2015 um 23:04 schrieb Richard (Rick) Karlquist:

Do you have a specific URL for "hacking oscillators"?  I can't
find it on Rubiola's web site.

Rick


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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Magnus Danielson]

It's chapter 6 in his phase noise book.

Cheers,
Magnus

On 10/28/2015 11:04 PM, Richard (Rick) Karlquist wrote:

Do you have a specific URL for "hacking oscillators"?  I can't
find it on Rubiola's web site.

Rick

On 10/28/2015 1:32 PM, Gerhard Hoffmann wrote:

Am 28.10.2015 um 19:22 schrieb KA2WEU--- via time-nuts:

This oscillator seems to have been more a frequency standard then a
noise
standard. Today's 10 MHz oscillators are different/better, such a
crystal is
no  longer available/made.

Yes. Rubiola gives it the credit of being able to be mass-produced, and
it _was_
one successful product. There is a section in "hacking oscillators" on
it;
my copy of the book is 200 miles away right now.

regards,

Gerhard, DK4XP


(see www.rubiola.org)
___

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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Gerhard Hoffmann]

Am 28.10.2015 um 23:04 schrieb Richard (Rick) Karlquist:

Do you have a specific URL for "hacking oscillators"?  I can't
find it on Rubiola's web site.

It is a chapter in his book where he analyzes the form of the noise spectra.
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bob Camp]

Hi

> On Oct 27, 2015, at 12:15 AM, Bruce Griffiths  
> wrote:
> 
> The 10811A ocxo uses an oscillator of this type albeit with a lower crystal 
> current, an overtone crystal. However the output stages spoil the PN 
> floor..Cascaded transformer coupled CB stages are somewhat quieter.

….. and since this is the region that the circuit really *is* the issue, 
lowering noise there is well worth doing. The target is 
basically signal to noise. That makes it much easier to analyze than some of 
the non-linear stuff that can impact the close in
noise. 

Bob


> Bruce
> 
> 
> 
> On Tuesday, 27 October 2015 2:31 PM, Bruce Griffiths 
>  wrote:
> 
> 
> Various versions of this oscillator circuit have been employed as high 
> stability OCXOs eg:
> 
> http://ri.search.yahoo.com/_ylt=AwrTcaxMzS5WgJIAMwk3QIpQ;_ylu=X3oDMTBzbW1zYXBzBHNlYwNzcgRwb3MDMjEEY29sbwNncTEEdnRpZAM-/RV=2/RE=1445936589/RO=10/RU=https%3a%2f%2fescies.org%2fdownload%2fwebDocumentFile%3fid%3d60902/RK=0/RS=.Rmksavr9Ui3TZ8D1XyZ06TpeDY-
> An AGC circuit can be employed to adjust the dc current of the oscillator 
> transistor to stabilise the crystal current.
> The circuit as given was merely intended to show an alternative to the 
> corresponding Wenzel version which employs a high input impedance buffer. The 
> Wenzel version has a relatively low oscillator transistor Vcb which is 
> perhaps somewhat undesirable.
> Driscoll developed various high frequency crystal oscillators employing MMICs 
> RF splitters together with a crystal, various matching circuits and a diode 
> limiter.  
> 
> Bruce 
> 
> 
> On Tuesday, 27 October 2015 2:01 PM, Bruce Griffiths 
>  wrote:
> 
> 
> On Tuesday, October 27, 2015 12:03:49 AM Attila Kinali wrote:
>> Hi,
>> 
>> I've been trying to read up on low noise crystal oscillators and had
>> a closer look at the design by Bruce Griffiths[1]. There are explanations
>> to how the circuit works, but I have some questions on the details.
>> I would appreciate if someone could answer these questions.
>> 
>> [1] http://www.ko4bb.com/~bruce/CrystalOscillators.html
>> 
>> 
>> I will do a short recap how the circuit works, just to make sure I
>> haven't misunderstood it.
>> 
>> The oscillator core is the colpitts oscillator build around Q104,
>> C107/108 form the driving/feedback path to form a negative resistance
>> over the quartz crystal. The resistors R112 and R113 are there only
>> to keep the crystal bias free and prevent charges from building up.
>> 
>> The output is formed using the crystal as filter to get rid of
>> harmonics and noise outside the crystal bandwidth. The "ground" point
>> of the crystal is formed using the low input impedance of the common
>> base amplifier formed by Q102. The output is coupled using a 
> transformer
>> to make it DC free and for impedance transformation.
>> 
>> Q103, LED102 and R116 form a constant current source for the collector
>> of Q104, using the base of Q104 as control input.
>> 
>> 
>> Q105 acts as a series voltage regulator, using multiple LM329's as
>> reference, which are averaged for lower noise and Q106 to compensate
>> for Q105's B-E voltage drop.
>> 
>> Q101 is the input power supply filter.
>> 
>> 
>> Now my questions:
>> 
>> Doesn't the non-zero input impedance of Q102 dampen the
>> crystal unnecessarily?
> The effect is relatively insignificant provided the crystal esr is 
> significantly 
> larger than the CB stage input R.
> With an overtone crystal this is readily achieved.
>> 
>> Why use a colpitts oscillator when using the crystal as output filter?
>> Wouldn't a Butler oscillator make more sense? Or is there some
>> disadvantage of Butler oscillator that I am not aware of?
>> 
>> 
> Avoiding doubling resistance in series with the crystal due to the 2 
> transistors of the butler configuration.
>> Why are LEDs used as voltage references? Don't they have a horrible
>> temperature coefficient and bad aging characteristics?
>> My guess would be that LED101 is not that critical as it will only
>> result in a slight change of the collector current and thus only
>> a slight change in the input impedance common base amplifier Q102.
>> 
> In both cases the LED forward voltage tempco is approximately matched 
> by the Vbe tempco of a transistor so that the resultant dc current is 
> nominally temperature independent.
> LEDs have relatively low noise however they are somewhat photosensitive.
> Using low noise dc bias circuits like these can significantly reduce the 
> close in phase noise of RF amplifiers significantly compared to a bias 
> circuit using a voltage divider from the power supply. 
>> 
>> Does the constant current source (Q103, LED 102, R116) sufficiently
>> stabilize the power inside the crystal, and thus the output power?
>> My guess would be that changes in h_fe of Q104 will result in
>> different biasing of Q104 and thus in changes of the power within the
>> crystal, which 

Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Richard (Rick) Karlquist]

On 10/26/2015 9:15 PM, Bruce Griffiths wrote:

The 10811A ocxo uses an oscillator of this type albeit with a lower crystal 
current, an overtone crystal. However the output stages spoil the PN 
floor..Cascaded transformer coupled CB stages are somewhat quieter.
Bruce



That's right. Burgoon (10811 designer) told me he had to meet other
requirements besides noise floor.  He had a special
one-off version of the 10811 without these compromises
that he built to provide a reference source to use
for phase noise measurements.  In the 10816 rubidium,
I used 3 common base transistors in cascade as
the output buffer and got similar results to
his special version.





Driscoll developed various high frequency crystal oscillators employing MMICs 
RF splitters together with a crystal, various matching circuits and a diode 
limiter.



Yes, he did, but long before that work he championed
his 2 transistor circuit that was extensively copied
by many other designers.

Rick
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bruce Griffiths]

As Rick has pointed out numerous times when the output signal is extracted via 
the crystal by a CB stage (or cascade thereof) the PN floor is determined by 
the ratio of the amplifier equivalent input noise current to the crystal 
current. That is the amplifier equivalent input noise current at frequencies 
for which the crystal impedance is high. If one neglects this crucial point one 
comes to the conclusion (e.g. see Eq 4.-1 page 274 of Ulrich Rohde's: Microwave 
and Wireless Synthesisers Theory and Design.) that with a crystal current of 
1.4mA rms and a crystal esr of 50 ohms that the XO PN floor cannot be lower 
than -154dBc/Hz.  Even the XO circuit in the ARRL handbook (attributed to 
Ulrich) using this method of signal extraction has a measured PN floor of 
-168dBc/Hz.  Many other XO's (including the 10811A which uses a crystal current 
of 1mA ) have an actual PN significantly lower than this.  One would have 
thought that this glaring discrepancy between "theory" and practice would 
 have been noticed and corrected by now.
Bruce 


 On Tuesday, 27 October 2015 6:01 PM, Richard (Rick) Karlquist 
 wrote:
   

 The oscillator transistor and buffer amplifier are basically
the same as the HP 10811, except for the absence of mode
suppressors.  The difference here is that the oscillator
self limits in the oscillator transistor, whereas the 10811
has ALC.  The discontinuous operation of the transistor,
as explained by Driscoll some 45 years ago, is undesirable
because it increases the load resistance the crystal sees.
The 2 transistor "Driscoll oscillator" fixes this problem
by using an additional stage that limits instead of the
oscillator transistor.  This has been widely used for
decades.  It is interesting to note that the 10811 ALC
works by varying the DC bias current in the oscillator
transistor.  This is in contrast to the elaborate DC
bias current stabilization here.

I have demonstrated that the close in phase noise in
the 10811 is entirely due to the flicker noise of the
crystal.  The only place where the 10811 circuit comes
into play is beyond 1 kHz from the carrier, where the
Burgoon patent circuit (which apparently has prior art
from Ulrich Rhode) reduces the phase noise floor.  I
have built two different oscillator circuits for 10811
crystals and have measured the flicker noise as being
the same as the intrinsic noise of the crystal.

Thus, obsessing over noise in oscillators circuits may
be overkill, unless you are planning to use a much
better crystal (BVA, etc).  OTOH, it might be advantageous
to improve the reverse isolation by adding additional
grounded base buffer stages.  There are various NBS/NIST
papers where several grounded base stages are cascaded.
I did this in the HP 10816 rubidium standard.

It is good to see time-nuts learning about oscillator
circuit by building them.

Rick Karlquist N6RK
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[KA2WEU--- via time-nuts]

I have bought and measured the hp10811 at about -174dBc/Hz.  The 
interesting  thing is  the feedback capacitor from collector  to base which 
changes 
Rin=1/gm.
 
Unless the circuit has a hidden Q mulitplier the PN (SSB) can never be  
better then 177 (kT) in dBm  + Pout  in dBm - NF of the  oscillator transistor. 
Many of the GB stages are potentially unstable , so the  "hopeful' best PN 
(SSB) is 177dbm + Pout !
 
AT 100 Mhz the leaing values are -146/100Hz offset  and - 183 far out  and 
high crystal dissipation, 2mW or so 
 
Ulrich 
 
 
In a message dated 10/27/2015 4:17:16 P.M. W. Europe Standard Time,  
bruce.griffi...@xtra.co.nz writes:

As Rick  has pointed out numerous times when the output signal is extracted 
via the  crystal by a CB stage (or cascade thereof) the PN floor is 
determined by the  ratio of the amplifier equivalent input noise current to the 
crystal current.  That is the amplifier equivalent input noise current at 
frequencies for which  the crystal impedance is high. If one neglects this 
crucial point one comes to  the conclusion (e.g. see Eq 4.-1 page 274 of Ulrich 
Rohde's: Microwave and  Wireless Synthesisers Theory and Design.) that with a 
crystal current of 1.4mA  rms and a crystal esr of 50 ohms that the XO PN 
floor cannot be lower than  -154dBc/Hz.  Even the XO circuit in the ARRL 
handbook (attributed to  Ulrich) using this method of signal extraction has a 
measured PN floor of  -168dBc/Hz.  Many other XO's (including the 10811A  which 
uses a crystal current of 1mA ) have an actual PN significantly lower  than 
this.  One would have thought that this glaring discrepancy  between 
"theory" and practice would have been noticed and corrected by  now.
Bruce 


On Tuesday, 27 October 2015 6:01  PM, Richard (Rick) Karlquist 
  wrote:


The oscillator transistor and buffer amplifier  are basically
the same as the HP 10811, except for the absence of  mode
suppressors.  The difference here is that the oscillator
self  limits in the oscillator transistor, whereas the 10811
has ALC.  The  discontinuous operation of the transistor,
as explained by Driscoll some 45  years ago, is undesirable
because it increases the load resistance the  crystal sees.
The 2 transistor "Driscoll oscillator" fixes this  problem
by using an additional stage that limits instead of  the
oscillator transistor.  This has been widely used  for
decades.  It is interesting to note that the 10811 ALC
works by  varying the DC bias current in the oscillator
transistor.  This is in  contrast to the elaborate DC
bias current stabilization here.

I have  demonstrated that the close in phase noise in
the 10811 is entirely due to  the flicker noise of the
crystal.  The only place where the 10811  circuit comes
into play is beyond 1 kHz from the carrier, where  the
Burgoon patent circuit (which apparently has prior art
from Ulrich  Rhode) reduces the phase noise floor.  I
have built two different  oscillator circuits for 10811
crystals and have measured the flicker noise  as being
the same as the intrinsic noise of the crystal.

Thus,  obsessing over noise in oscillators circuits may
be overkill, unless you  are planning to use a much
better crystal (BVA, etc).  OTOH, it might  be advantageous
to improve the reverse isolation by adding  additional
grounded base buffer stages.  There are various  NBS/NIST
papers where several grounded base stages are cascaded.
I did  this in the HP 10816 rubidium standard.

It is good to see time-nuts  learning about oscillator
circuit by building them.

Rick Karlquist  N6RK
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[time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Attila Kinali]

Hi,

I've been trying to read up on low noise crystal oscillators and had
a closer look at the design by Bruce Griffiths[1]. There are explanations
to how the circuit works, but I have some questions on the details.
I would appreciate if someone could answer these questions.

[1] http://www.ko4bb.com/~bruce/CrystalOscillators.html


I will do a short recap how the circuit works, just to make sure I 
haven't misunderstood it.

The oscillator core is the colpitts oscillator build around Q104,
C107/108 form the driving/feedback path to form a negative resistance
over the quartz crystal. The resistors R112 and R113 are there only
to keep the crystal bias free and prevent charges from building up.

The output is formed using the crystal as filter to get rid of
harmonics and noise outside the crystal bandwidth. The "ground" point
of the crystal is formed using the low input impedance of the common
base amplifier formed by Q102. The output is coupled using a transformer
to make it DC free and for impedance transformation.

Q103, LED102 and R116 form a constant current source for the collector
of Q104, using the base of Q104 as control input.


Q105 acts as a series voltage regulator, using multiple LM329's as
reference, which are averaged for lower noise and Q106 to compensate
for Q105's B-E voltage drop.

Q101 is the input power supply filter.


Now my questions:

Doesn't the non-zero input impedance of Q102 dampen the
crystal unnecessarily?

Why use a colpitts oscillator when using the crystal as output filter?
Wouldn't a Butler oscillator make more sense? Or is there some
disadvantage of Butler oscillator that I am not aware of?


Why are LEDs used as voltage references? Don't they have a horrible
temperature coefficient and bad aging characteristics?
My guess would be that LED101 is not that critical as it will only
result in a slight change of the collector current and thus only
a slight change in the input impedance common base amplifier Q102.


Does the constant current source (Q103, LED 102, R116) sufficiently
stabilize the power inside the crystal, and thus the output power?
My guess would be that changes in h_fe of Q104 will result in
different biasing of Q104 and thus in changes of the power within the
crystal, which then affects frequency and aging.

Can the noise induced by Q103 be further decreased by increasing C109?
Or is there a reason why C109 is just 10nF? Stability maybe?
If stability is the problem, how about using an RC low pass filter?

If one would want to make this circuit tunable, where would the
varicap get connected to? My guess would be on the right side of
the crystal, between the crystal and C105, going to ground
The bias voltage would be then applied directly at the crystal/C105/varicap 
node. Is this correct or is there a better way?


What are the criteria to choose the transistors?

Thanks in advance

Attila Kinali

-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bruce Griffiths]

On Tuesday, October 27, 2015 12:03:49 AM Attila Kinali wrote:
> Hi,
> 
> I've been trying to read up on low noise crystal oscillators and had
> a closer look at the design by Bruce Griffiths[1]. There are explanations
> to how the circuit works, but I have some questions on the details.
> I would appreciate if someone could answer these questions.
> 
> [1] http://www.ko4bb.com/~bruce/CrystalOscillators.html
> 
> 
> I will do a short recap how the circuit works, just to make sure I
> haven't misunderstood it.
> 
> The oscillator core is the colpitts oscillator build around Q104,
> C107/108 form the driving/feedback path to form a negative resistance
> over the quartz crystal. The resistors R112 and R113 are there only
> to keep the crystal bias free and prevent charges from building up.
> 
> The output is formed using the crystal as filter to get rid of
> harmonics and noise outside the crystal bandwidth. The "ground" point
> of the crystal is formed using the low input impedance of the common
> base amplifier formed by Q102. The output is coupled using a 
transformer
> to make it DC free and for impedance transformation.
> 
> Q103, LED102 and R116 form a constant current source for the collector
> of Q104, using the base of Q104 as control input.
> 
> 
> Q105 acts as a series voltage regulator, using multiple LM329's as
> reference, which are averaged for lower noise and Q106 to compensate
> for Q105's B-E voltage drop.
> 
> Q101 is the input power supply filter.
> 
> 
> Now my questions:
> 
> Doesn't the non-zero input impedance of Q102 dampen the
> crystal unnecessarily?
The effect is relatively insignificant provided the crystal esr is 
significantly 
larger than the CB stage input R.
With an overtone crystal this is readily achieved.
> 
> Why use a colpitts oscillator when using the crystal as output filter?
> Wouldn't a Butler oscillator make more sense? Or is there some
> disadvantage of Butler oscillator that I am not aware of?
> 
> 
Avoiding doubling resistance in series with the crystal due to the 2 
transistors of the butler configuration.
> Why are LEDs used as voltage references? Don't they have a horrible
> temperature coefficient and bad aging characteristics?
> My guess would be that LED101 is not that critical as it will only
> result in a slight change of the collector current and thus only
> a slight change in the input impedance common base amplifier Q102.
> 
In both cases the LED forward voltage tempco is approximately matched 
by the Vbe tempco of a transistor so that the resultant dc current is 
nominally temperature independent.
LEDs have relatively low noise however they are somewhat photosensitive.
Using low noise dc bias circuits like these can significantly reduce the 
close in phase noise of RF amplifiers significantly compared to a bias 
circuit using a voltage divider from the power supply. 
> 
> Does the constant current source (Q103, LED 102, R116) sufficiently
> stabilize the power inside the crystal, and thus the output power?
> My guess would be that changes in h_fe of Q104 will result in
> different biasing of Q104 and thus in changes of the power within the
> crystal, which then affects frequency and aging.
> 
The colpitts oscillator  transistor in this circuit operates in a discontinuous 
mode. 

> Can the noise induced by Q103 be further decreased by increasing 
C109?
> Or is there a reason why C109 is just 10nF? Stability maybe?
> If stability is the problem, how about using an RC low pass filter?
the noise contribution by Q103 isnt significant.
Yes bias loop stability is an issue you cant just insert arbitrary low pass RC 
filters some design effort is required.
> 
> If one would want to make this circuit tunable, where would the
> varicap get connected to? My guess would be on the right side of
> the crystal, between the crystal and C105, going to ground
> The bias voltage would be then applied directly at the 
crystal/C105/varicap
> node. Is this correct or is there a better way?
> 
In series with C105 is a far better location.
You may then need to increase the value of C105.
> 
> What are the criteria to choose the transistors?
> 
Low flicker noise and sufficient RF gain at the crystal frequency.

> Thanks in advance
> 
>   Attila Kinali
Bruce
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Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bruce Griffiths]

The 10811A ocxo uses an oscillator of this type albeit with a lower crystal 
current, an overtone crystal. However the output stages spoil the PN 
floor..Cascaded transformer coupled CB stages are somewhat quieter.
Bruce
 


 On Tuesday, 27 October 2015 2:31 PM, Bruce Griffiths 
 wrote:
   

 Various versions of this oscillator circuit have been employed as high 
stability OCXOs eg:

http://ri.search.yahoo.com/_ylt=AwrTcaxMzS5WgJIAMwk3QIpQ;_ylu=X3oDMTBzbW1zYXBzBHNlYwNzcgRwb3MDMjEEY29sbwNncTEEdnRpZAM-/RV=2/RE=1445936589/RO=10/RU=https%3a%2f%2fescies.org%2fdownload%2fwebDocumentFile%3fid%3d60902/RK=0/RS=.Rmksavr9Ui3TZ8D1XyZ06TpeDY-
An AGC circuit can be employed to adjust the dc current of the oscillator 
transistor to stabilise the crystal current.
The circuit as given was merely intended to show an alternative to the 
corresponding Wenzel version which employs a high input impedance buffer. The 
Wenzel version has a relatively low oscillator transistor Vcb which is perhaps 
somewhat undesirable.
Driscoll developed various high frequency crystal oscillators employing MMICs 
RF splitters together with a crystal, various matching circuits and a diode 
limiter.  

Bruce 


 On Tuesday, 27 October 2015 2:01 PM, Bruce Griffiths 
 wrote:
   

 On Tuesday, October 27, 2015 12:03:49 AM Attila Kinali wrote:
> Hi,
> 
> I've been trying to read up on low noise crystal oscillators and had
> a closer look at the design by Bruce Griffiths[1]. There are explanations
> to how the circuit works, but I have some questions on the details.
> I would appreciate if someone could answer these questions.
> 
> [1] http://www.ko4bb.com/~bruce/CrystalOscillators.html
> 
> 
> I will do a short recap how the circuit works, just to make sure I
> haven't misunderstood it.
> 
> The oscillator core is the colpitts oscillator build around Q104,
> C107/108 form the driving/feedback path to form a negative resistance
> over the quartz crystal. The resistors R112 and R113 are there only
> to keep the crystal bias free and prevent charges from building up.
> 
> The output is formed using the crystal as filter to get rid of
> harmonics and noise outside the crystal bandwidth. The "ground" point
> of the crystal is formed using the low input impedance of the common
> base amplifier formed by Q102. The output is coupled using a 
transformer
> to make it DC free and for impedance transformation.
> 
> Q103, LED102 and R116 form a constant current source for the collector
> of Q104, using the base of Q104 as control input.
> 
> 
> Q105 acts as a series voltage regulator, using multiple LM329's as
> reference, which are averaged for lower noise and Q106 to compensate
> for Q105's B-E voltage drop.
> 
> Q101 is the input power supply filter.
> 
> 
> Now my questions:
> 
> Doesn't the non-zero input impedance of Q102 dampen the
> crystal unnecessarily?
The effect is relatively insignificant provided the crystal esr is 
significantly 
larger than the CB stage input R.
With an overtone crystal this is readily achieved.
> 
> Why use a colpitts oscillator when using the crystal as output filter?
> Wouldn't a Butler oscillator make more sense? Or is there some
> disadvantage of Butler oscillator that I am not aware of?
> 
> 
Avoiding doubling resistance in series with the crystal due to the 2 
transistors of the butler configuration.
> Why are LEDs used as voltage references? Don't they have a horrible
> temperature coefficient and bad aging characteristics?
> My guess would be that LED101 is not that critical as it will only
> result in a slight change of the collector current and thus only
> a slight change in the input impedance common base amplifier Q102.
> 
In both cases the LED forward voltage tempco is approximately matched 
by the Vbe tempco of a transistor so that the resultant dc current is 
nominally temperature independent.
LEDs have relatively low noise however they are somewhat photosensitive.
Using low noise dc bias circuits like these can significantly reduce the 
close in phase noise of RF amplifiers significantly compared to a bias 
circuit using a voltage divider from the power supply. 
> 
> Does the constant current source (Q103, LED 102, R116) sufficiently
> stabilize the power inside the crystal, and thus the output power?
> My guess would be that changes in h_fe of Q104 will result in
> different biasing of Q104 and thus in changes of the power within the
> crystal, which then affects frequency and aging.
> 
The colpitts oscillator  transistor in this circuit operates in a discontinuous 
mode. 

> Can the noise induced by Q103 be further decreased by increasing 
C109?
> Or is there a reason why C109 is just 10nF? Stability maybe?
> If stability is the problem, how about using an RC low pass filter?
the noise contribution by Q103 isnt significant.
Yes bias loop stability is an issue you cant just insert arbitrary low pass RC 
filters some design effort is required.
> 
> If 

Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Richard (Rick) Karlquist]

The oscillator transistor and buffer amplifier are basically
the same as the HP 10811, except for the absence of mode
suppressors.  The difference here is that the oscillator
self limits in the oscillator transistor, whereas the 10811
has ALC.  The discontinuous operation of the transistor,
as explained by Driscoll some 45 years ago, is undesirable
because it increases the load resistance the crystal sees.
The 2 transistor "Driscoll oscillator" fixes this problem
by using an additional stage that limits instead of the
oscillator transistor.  This has been widely used for
decades.  It is interesting to note that the 10811 ALC
works by varying the DC bias current in the oscillator
transistor.  This is in contrast to the elaborate DC
bias current stabilization here.

I have demonstrated that the close in phase noise in
the 10811 is entirely due to the flicker noise of the
crystal.  The only place where the 10811 circuit comes
into play is beyond 1 kHz from the carrier, where the
Burgoon patent circuit (which apparently has prior art
from Ulrich Rhode) reduces the phase noise floor.  I
have built two different oscillator circuits for 10811
crystals and have measured the flicker noise as being
the same as the intrinsic noise of the crystal.

Thus, obsessing over noise in oscillators circuits may
be overkill, unless you are planning to use a much
better crystal (BVA, etc).  OTOH, it might be advantageous
to improve the reverse isolation by adding additional
grounded base buffer stages.  There are various NBS/NIST
papers where several grounded base stages are cascaded.
I did this in the HP 10816 rubidium standard.

It is good to see time-nuts learning about oscillator
circuit by building them.

Rick Karlquist N6RK
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and follow the instructions there.

Re: [time-nuts] Low noise quartz crystal oscillator by Bruce Griffiths

[Bruce Griffiths]

Various versions of this oscillator circuit have been employed as high 
stability OCXOs eg:

http://ri.search.yahoo.com/_ylt=AwrTcaxMzS5WgJIAMwk3QIpQ;_ylu=X3oDMTBzbW1zYXBzBHNlYwNzcgRwb3MDMjEEY29sbwNncTEEdnRpZAM-/RV=2/RE=1445936589/RO=10/RU=https%3a%2f%2fescies.org%2fdownload%2fwebDocumentFile%3fid%3d60902/RK=0/RS=.Rmksavr9Ui3TZ8D1XyZ06TpeDY-
An AGC circuit can be employed to adjust the dc current of the oscillator 
transistor to stabilise the crystal current.
The circuit as given was merely intended to show an alternative to the 
corresponding Wenzel version which employs a high input impedance buffer. The 
Wenzel version has a relatively low oscillator transistor Vcb which is perhaps 
somewhat undesirable.
Driscoll developed various high frequency crystal oscillators employing MMICs 
RF splitters together with a crystal, various matching circuits and a diode 
limiter.  

Bruce 


 On Tuesday, 27 October 2015 2:01 PM, Bruce Griffiths 
 wrote:
   

 On Tuesday, October 27, 2015 12:03:49 AM Attila Kinali wrote:
> Hi,
> 
> I've been trying to read up on low noise crystal oscillators and had
> a closer look at the design by Bruce Griffiths[1]. There are explanations
> to how the circuit works, but I have some questions on the details.
> I would appreciate if someone could answer these questions.
> 
> [1] http://www.ko4bb.com/~bruce/CrystalOscillators.html
> 
> 
> I will do a short recap how the circuit works, just to make sure I
> haven't misunderstood it.
> 
> The oscillator core is the colpitts oscillator build around Q104,
> C107/108 form the driving/feedback path to form a negative resistance
> over the quartz crystal. The resistors R112 and R113 are there only
> to keep the crystal bias free and prevent charges from building up.
> 
> The output is formed using the crystal as filter to get rid of
> harmonics and noise outside the crystal bandwidth. The "ground" point
> of the crystal is formed using the low input impedance of the common
> base amplifier formed by Q102. The output is coupled using a 
transformer
> to make it DC free and for impedance transformation.
> 
> Q103, LED102 and R116 form a constant current source for the collector
> of Q104, using the base of Q104 as control input.
> 
> 
> Q105 acts as a series voltage regulator, using multiple LM329's as
> reference, which are averaged for lower noise and Q106 to compensate
> for Q105's B-E voltage drop.
> 
> Q101 is the input power supply filter.
> 
> 
> Now my questions:
> 
> Doesn't the non-zero input impedance of Q102 dampen the
> crystal unnecessarily?
The effect is relatively insignificant provided the crystal esr is 
significantly 
larger than the CB stage input R.
With an overtone crystal this is readily achieved.
> 
> Why use a colpitts oscillator when using the crystal as output filter?
> Wouldn't a Butler oscillator make more sense? Or is there some
> disadvantage of Butler oscillator that I am not aware of?
> 
> 
Avoiding doubling resistance in series with the crystal due to the 2 
transistors of the butler configuration.
> Why are LEDs used as voltage references? Don't they have a horrible
> temperature coefficient and bad aging characteristics?
> My guess would be that LED101 is not that critical as it will only
> result in a slight change of the collector current and thus only
> a slight change in the input impedance common base amplifier Q102.
> 
In both cases the LED forward voltage tempco is approximately matched 
by the Vbe tempco of a transistor so that the resultant dc current is 
nominally temperature independent.
LEDs have relatively low noise however they are somewhat photosensitive.
Using low noise dc bias circuits like these can significantly reduce the 
close in phase noise of RF amplifiers significantly compared to a bias 
circuit using a voltage divider from the power supply. 
> 
> Does the constant current source (Q103, LED 102, R116) sufficiently
> stabilize the power inside the crystal, and thus the output power?
> My guess would be that changes in h_fe of Q104 will result in
> different biasing of Q104 and thus in changes of the power within the
> crystal, which then affects frequency and aging.
> 
The colpitts oscillator  transistor in this circuit operates in a discontinuous 
mode. 

> Can the noise induced by Q103 be further decreased by increasing 
C109?
> Or is there a reason why C109 is just 10nF? Stability maybe?
> If stability is the problem, how about using an RC low pass filter?
the noise contribution by Q103 isnt significant.
Yes bias loop stability is an issue you cant just insert arbitrary low pass RC 
filters some design effort is required.
> 
> If one would want to make this circuit tunable, where would the
> varicap get connected to? My guess would be on the right side of
> the crystal, between the crystal and C105, going to ground
> The bias voltage would be then applied directly at the 
crystal/C105/varicap
> node. Is this correct or is there a better way?
> 
In