Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Henk

Henk ten Pierick wrote:
>> Meanwhile look at:
>>
>> http://www.ko4bb.com/~bruce/LPND.html
>> 
>> 
>
> I did and it was very helpful
>
>   
>> This crystal oscillator circuit is a variant of the low noise  
>> oscillator
>> proposed by Wenzel for use with fundamental crystals. It uses a common
>> base buffer and demonstrates several low noise biasing techniques that
>> can be used.
>> 
>
> The schematic is easy to understand, but it is not clear to me what  
> defines the xtal current. The loading of the oscillator due to the  
> base resistor of 10k is surprising. I expected a controlled loop for  
> the xtal current in a well designed oscillator.
> How high or low is the loaded Q. How is noise matching for the  
> oscillator defined?
>
>   
Crystal current is defined by the dc current in Q104.
To adjust the crystal current adjust R116.
To see the effect you need to either build or simulate the circuit
(difficult without the right software).
The 10K is connected in parallel (as far as the RF is concerned) with
C107 and C108. (C107 has a reactance of around )
Its actually difficult to make a choke that has an equivalent shunt R as
large as 10K.
If you are worried about it R114 it can be increased to 100K.
The oscillator transistor turns on for a small part of the RF cycle.
Optimising the duty cycle by adjusting the ratio of C107 to C108 can
improve the phase noise.
Noise matching has little relevance for flicker phase noise.
Loaded Q is quite high.
>> The 2nd and third references above the oscillator schematic explain  
>> the
>> mechanisms for generating AM and PM noise in a BJT RF amplifier. The
>> derivation is quite mathematical (statistics and calculus) but the
>> conclusions are relatively simple.
>> 
>
> Nice reading with clear conclusions. A lot of the cited measures and  
> comments from you and other  time nuts are now better understood.
>
>   
>> To drive an HC04 the common base buffer can use a load consisting  
>> of an
>> inductor shunted by a resistor to develop the drive. The shunt  
>> inductor
>> reduces the dc gain (from base to collector) of the  buffer stage and
>> hence the low frequency noise voltage developed across the collector
>> base capacitance. Such noise voltages modulate the output capacitance
>> and hence the phase shift of the buffer, increasing the buffer phase
>> noise.  Nonlinearities such as hfe variation with current tend to
>> increase the buffer output AM noise not the PM noise.
>> 
>
> It is funny that I always tried to avoid coils because of sensitivity  
> for magnetic fields and now I learn that I have to use coils for the  
> lowest phase noise. Why is there not an inductor used i.s.o a  
> resistor of 10k in the base of Q104? Avoids the loading with the  
> consequence that xtail current control has to be done in an other way.
>
>   
Actually real inductors have finite equivalent shunt R, in practice its
difficult to get much above 10K without special techniques and
relatively large physical size.
Increasing R114 to 100K is probably a good idea in that it reduces the
series equivalent from 2.5ohms (a bit high)) to about 0.25 ohms. 
This will not increase the flicker phase noise.
Increasing C107 and C108 will also reduce the effective ESR due to R114.
> I assume that the loaded Q of the oscillator is important for a low  
> phase noise. The circuit suggests different. Am I missing something?
>
> Henk
>   
Circuit Q is higher than you think.

If you only want a CMOS output a lower phase noise oscillator is
possible using 1 diode and 1 transistor less than in your circuit.
I'll add it to the collection of additional crystal oscillator circuits at:
http://www.ko4bb.com/~bruce/XTALOSC.html


Yes, biasing of the CMOS gate appears weird but it works well.

Bruce
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Re: [time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

On Jan 2, 2008, at 0:06, Bruce Griffiths wrote:

>>
> Henk
>
> The circuit diagram helps a lot.

Thanks a lot for the comments on the schematic, they explain a lot.

> I will create some circuit schematics for crystal oscillators that
> control the crystal current more directly and use a common base output
> buffer.

thanks in advance

> Meanwhile look at:
>
> http://www.ko4bb.com/~bruce/LPND.html
> 

I did and it was very helpful

> This crystal oscillator circuit is a variant of the low noise  
> oscillator
> proposed by Wenzel for use with fundamental crystals. It uses a common
> base buffer and demonstrates several low noise biasing techniques that
> can be used.

The schematic is easy to understand, but it is not clear to me what  
defines the xtal current. The loading of the oscillator due to the  
base resistor of 10k is surprising. I expected a controlled loop for  
the xtal current in a well designed oscillator.
How high or low is the loaded Q. How is noise matching for the  
oscillator defined?

> The 2nd and third references above the oscillator schematic explain  
> the
> mechanisms for generating AM and PM noise in a BJT RF amplifier. The
> derivation is quite mathematical (statistics and calculus) but the
> conclusions are relatively simple.

Nice reading with clear conclusions. A lot of the cited measures and  
comments from you and other  time nuts are now better understood.

> To drive an HC04 the common base buffer can use a load consisting  
> of an
> inductor shunted by a resistor to develop the drive. The shunt  
> inductor
> reduces the dc gain (from base to collector) of the  buffer stage and
> hence the low frequency noise voltage developed across the collector
> base capacitance. Such noise voltages modulate the output capacitance
> and hence the phase shift of the buffer, increasing the buffer phase
> noise.  Nonlinearities such as hfe variation with current tend to
> increase the buffer output AM noise not the PM noise.

It is funny that I always tried to avoid coils because of sensitivity  
for magnetic fields and now I learn that I have to use coils for the  
lowest phase noise. Why is there not an inductor used i.s.o a  
resistor of 10k in the base of Q104? Avoids the loading with the  
consequence that xtail current control has to be done in an other way.

I assume that the loaded Q of the oscillator is important for a low  
phase noise. The circuit suggests different. Am I missing something?

Henk
  

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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Henk

If the real part of the impedance (at resonance) at the base of the
oscillator transistor is high this will significantly increase the real
part of the impedance at the emitter of the oscillator transistor seen
by the crystal thus decreasing its loaded Q. The real part of the
impedance of the tuned circuit at the oscillator base is likely to be
quite high (several kohm) at resonance and depending on the transformer
turns ratio the real part of the impedance seen by the base of the
oscillator transistor may also be significant.

Bruce

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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Grant Hodgson wrote:
> Henk ten Pierick wrote:
> --snip--
>   
>> It showed to be very difficult to come lower than what I have now. If 
>> can be the crystal. How can I decide?
>> 
>
> As an absolute minimum, you need to know the crystal dynamic (or 
> motional) parameters - the crystal supplier should be able to provide 
> these.  If not, you can measure them on a network analyser whilst you 
> look for another crystal supplier.
>
>   

> Then you should be able to simulate the phase noise of the oscillator 
> using a harmonic balance or similar method as used in Microwave Office, 
> Genesys, ADS, Ansoft Desginer, QUCS etc.  Failing that, a small-signal 
> (linear) open-loop analysis would at least give an estimate of the 
> loaded Q, which can be used to predict phase noise - but ignoring 
> flicker noise.  Some SPICE-based simulators might be able to help.
>
>   
The circuit is so simple that one can easily estimate the crystal loaded
Q by hand (if one knows the crystal parameters).
Similarly the phase noise floor can easily be estimated without
requiring a simulator.
Unless the simulators include physically correct models for the flicker
phase noise generation mechanisms they will be of little help.
If they persist in using the Leeson model (which has been shown to be a
gross approximation particularly for flicker noise by Hajimiri and Lee
as well as Demir), then the results are questionable.
With the correct flicker phase noise generation mechanism model its not
too difficult to estimate the flicker phase noise if one has sufficient
data on the oscillator transistor characteristics
Since real crystals exhibit flicker noise such estimates will need to be
supplemented by actual measurements.

If the crystal is a fundamental crystal similar to those offered by
cemac in an HC49 holder and is not a strip crystal then the ESR will be
less than 35 ohms (typically 20ohms??) so with a 5mA oscillator
transistor emitter current the loaded Q will be ~25% less than the
unloaded Q with if the crystal ESR is 20 ohms.
> --snip--
>   
>> I used the BC375 for the low Rbb' and assume that the noise corner must 
>> be low as a result of that. Is this not true?
>> 
>
> There are many different types of noise - the base bulk resistance of a 
> transistor contributes to shot noise, which is close to being 'white' - 
>   
rbb adds Johnson noise not shot noise.
> i.e. equal magnitude /Hz at all frequencies.  This does not have a 
> significant effect on phase noise at offsets close to the carrier, and 
> at 30Hz offset the flicker noise dominates.
Not necessarily true, RF phase noise may have either a higher or lower
flicker noise corner frequency than the transistors low frequency
flicker noise corner.
>   Flicker noise is not 
> 'white' noise - flicker noise increases at a rate of 1/f, or 10dB/decade 
> as the offset frequency is reduced, and simply choosing a transistor 
> with low Rbb' is not sufficient - the noise mechanisms are different.
>   
Increasing the junction area of the transistor reduces the low frequency
flicker noise however this increases the junction capacitances which
increases the Rf flicker phase noise.
It has recently been shown that flicker noise has a lower limit which is
quantum mechanical in nature.
> For an 11MHz oscillator I would use 2N5179s as advocated by Rick for 
> both the sustaining amplifier and the limiter - this is a very popular 
> transistor for oscillators in this frequency range.  I'd be surprised if 
> the BC375 generated less noise than the 2N5179.  This would mean 
> changing the circuit topology to use an NPN transistor instead of the 
> BF450 which is PNP.
>
>   
Using transistors with low capacitance can be more important than using
a lower noise transistor see:

http://tf.nist.gov/timefreq/general/pdf/1134.pdf

http://tf.nist.gov/timefreq/general/pdf/1139.pdf


>   
>>> At 11MHz, most crystal oscillators use parallel resonant crystals,
>>> although some are series resonant, such as the excellent Driscoll
>>> oscillator which is capable of the performance you desire with a
>>> suitable crystal.
>>>   
>> I was aware that most lower frequency circuits are parallel resonant. I 
>> used series in class A because I thought is was better, it is easier to 
>> use the current though the xtal. Is there a fundamental difference 
>> between parallel ore series w.r.t performance?
>> 
>
> Not really, it's the circuit topology determines whether a parallel or 
> series resonant crystal is used.  Your circuit appears to be a variant 
> of the Driscoll oscillator, which usually uses a series resonant crystal 
> and is capable of exceptionally high performance, however there are a 
> number of differences in your circuit, which I've never seen before, 
> although I can't claim to be an expert oscillator designer.  Circuit 
> simulation is a good (no - essential) starting point, and would give you 
> a good idea of the relative merits of the features of your circuit.
>
>   
Th

Re: [time-nuts] xtal oscillator phase noise, parallel versus series

[Richard (Rick) Karlquist]

I forgot to mention that the crystals for the E1938A had to
be calibrated for series resonance at 10 MHz.

Rick Karlquist N6RK

Didier Juges wrote:
> I think the main difference between parallel and series resonance is that in 
> parallel resonance mode, the capacitance of the crystal holder and wiring to 
> the crystal is part of the frequency determining parameters, and in series 
> mode it is not. So it may have a slight effect on temperature stability 
> (series would be better?) but it should have no other effect. 
> 
> If the parasitics are well controlled, it should have the same stability.
> 
> The crystal is operating the same way, at a slightly different frequency, so 
> if you had it specified for a series mode, you would be on the wrong 
> frequency if you put it into a parallel resonant mode oscillator..
> 
> Didier KO4BB
> 
> 
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Re: [time-nuts] xtal oscillator phase noise, parallel versus series

[Didier Juges]

I think the main difference between parallel and series resonance is that in 
parallel resonance mode, the capacitance of the crystal holder and wiring to 
the crystal is part of the frequency determining parameters, and in series mode 
it is not. So it may have a slight effect on temperature stability (series 
would be better?) but it should have no other effect. 

If the parasitics are well controlled, it should have the same stability.

The crystal is operating the same way, at a slightly different frequency, so if 
you had it specified for a series mode, you would be on the wrong frequency if 
you put it into a parallel resonant mode oscillator..

Didier KO4BB


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Re: [time-nuts] xtal oscillator phase noise

[Richard (Rick) Karlquist]

> Not really, it's the circuit topology determines whether a parallel or 
> series resonant crystal is used.  Your circuit appears to be a variant 

Just a comment about series vs parallel.  The 10811 has a parallel
resonant circuit and the E1938A has a series resonant circuit.
The crystals used are identical except for the package.  The performance
is basically identical.  There is nothing significant about
series vs parallel in terms of phase noise.

Rick Karlquist N6RK

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Re: [time-nuts] xtal oscillator phase noise

[Grant Hodgson]

Henk ten Pierick wrote:
--snip--
> 
> It showed to be very difficult to come lower than what I have now. If 
> can be the crystal. How can I decide?

As an absolute minimum, you need to know the crystal dynamic (or 
motional) parameters - the crystal supplier should be able to provide 
these.  If not, you can measure them on a network analyser whilst you 
look for another crystal supplier.

Then you should be able to simulate the phase noise of the oscillator 
using a harmonic balance or similar method as used in Microwave Office, 
Genesys, ADS, Ansoft Desginer, QUCS etc.  Failing that, a small-signal 
(linear) open-loop analysis would at least give an estimate of the 
loaded Q, which can be used to predict phase noise - but ignoring 
flicker noise.  Some SPICE-based simulators might be able to help.

--snip--
> 
> I used the BC375 for the low Rbb' and assume that the noise corner must 
> be low as a result of that. Is this not true?

There are many different types of noise - the base bulk resistance of a 
transistor contributes to shot noise, which is close to being 'white' - 
i.e. equal magnitude /Hz at all frequencies.  This does not have a 
significant effect on phase noise at offsets close to the carrier, and 
at 30Hz offset the flicker noise dominates.  Flicker noise is not 
'white' noise - flicker noise increases at a rate of 1/f, or 10dB/decade 
as the offset frequency is reduced, and simply choosing a transistor 
with low Rbb' is not sufficient - the noise mechanisms are different.

For an 11MHz oscillator I would use 2N5179s as advocated by Rick for 
both the sustaining amplifier and the limiter - this is a very popular 
transistor for oscillators in this frequency range.  I'd be surprised if 
the BC375 generated less noise than the 2N5179.  This would mean 
changing the circuit topology to use an NPN transistor instead of the 
BF450 which is PNP.


>> At 11MHz, most crystal oscillators use parallel resonant crystals,
>> although some are series resonant, such as the excellent Driscoll
>> oscillator which is capable of the performance you desire with a
>> suitable crystal.
> 
> I was aware that most lower frequency circuits are parallel resonant. I 
> used series in class A because I thought is was better, it is easier to 
> use the current though the xtal. Is there a fundamental difference 
> between parallel ore series w.r.t performance?

Not really, it's the circuit topology determines whether a parallel or 
series resonant crystal is used.  Your circuit appears to be a variant 
of the Driscoll oscillator, which usually uses a series resonant crystal 
and is capable of exceptionally high performance, however there are a 
number of differences in your circuit, which I've never seen before, 
although I can't claim to be an expert oscillator designer.  Circuit 
simulation is a good (no - essential) starting point, and would give you 
a good idea of the relative merits of the features of your circuit.

--snip--
> 
> I do normally not have access to a FSUP but borrowed the instrument for 
> two weeks. To my luck it has the B60 option and I used this of coarse. 
> There must be a reason for my employer to buy this fantastic tool.
> 
> Henk
> 

OK, but given that the noise level is currently way above the noise 
floor of the FSUP, using cross-correlation doesn't add anything - it 
just slows down the measurement.  Cross-correlation would only be of 
benefit to reduce the noise floor of the instrument if/when the phase 
noise of the oscillator has been reduced enough to justify it - it can 
seriously slow down the measurement.

regards

Grant
> 


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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Henk ten Pierick wrote:
> Bruce,
>
> 1.  Best wishes.
>
> 2. It has taken some time but here is the schematic.
>
> Henk
>
Henk

The circuit diagram helps a lot.

1) Since the crystal current is 1mA the RF voltage across R2 (and the RF
at the input of the HC04) is 220mV rms (622mV pp).
This is a little low as HC04's are a little noisy a higher input voltage
slew rate should help. Ideally about 1.75vrms or so (just avoids
clipping by the HC04 input protection diodes) should significantly
reduce the noise contribution from the HC04.

2) Emitter follower Q4 has a relatively low collector base voltage which
increases the collector base capacitance and associated phase noise. AC
coupling the emitter follower would allow a much higher collector base
voltage, and an inductor in series with the emitter resistor will allow
the emitter to swing below ground.

3) Your AGC circuit  seems to control the  feedback voltage/current at
the oscillator transistor base. An AGC in a crystal oscillator is
typically used to control the crystal current, you circuit doesnt appear
to do this directly.

4) The emitter follower will not drive a 50 ohm load without severe
distortion unless the emitter current is increased. Its not just the
output impedance (with zero input) that is important.

5) As Rick stated a common base buffer circuit would have better
performance. A common base circuit has no difficulty when driving a 50
ohm load. A step down transformer between the common base collector and
the load increases the RF voltage across the load.

6) A good buried zener has lower noise than the ADR445. The noise specs
for the ADR445 are somewhat sparse in that the spectral distribution of
the noise isnt given. One can always reduce the noise by averaging the
output of several references

7) Unless you need a tuned circuit to supress oscillation at unwanted
crystal modes, then using a circuit without one will provide better
temperature stability. If the tuned circuit uses ferrites then they may
increase the flicker phase noise.

8) If you do need a tuned circuit to suppress unwanted crystal modes
then one (there are many) of the Driscoll crystal oscillators is a good
solution.

9) The minimum ft of Q1 is a little low.

I will create some circuit schematics for crystal oscillators that
control the crystal current more directly and use a common base output
buffer.

Meanwhile look at:

http://www.ko4bb.com/~bruce/LPND.html


This crystal oscillator circuit is a variant of the low noise oscillator
proposed by Wenzel for use with fundamental crystals. It uses a common
base buffer and demonstrates several low noise biasing techniques that
can be used.

The 2nd and third references above the oscillator schematic explain the
mechanisms for generating AM and PM noise in a BJT RF amplifier. The
derivation is quite mathematical (statistics and calculus) but the
conclusions are relatively simple.

To drive an HC04 the common base buffer can use a load consisting of an
inductor shunted by a resistor to develop the drive. The shunt inductor
reduces the dc gain (from base to collector) of the  buffer stage and
hence the low frequency noise voltage developed across the collector
base capacitance. Such noise voltages modulate the output capacitance
and hence the phase shift of the buffer, increasing the buffer phase
noise.  Nonlinearities such as hfe variation with current tend to
increase the buffer output AM noise not the PM noise.

Bruce


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Re: [time-nuts] xtal oscillator phase noise

[Richard (Rick) Karlquist]

In the HP 10816 Rb frequency standard, we used a modified
10811 oscillator circuit.  The oscillator and first buffer
amplifier transistor were the same, but the rest of the
buffer amplifier was replaced with a cascaded grounded
base buffer amplifier.  We were able to get numbers comparable
to those shown below.  The ultimate limit at large offsets
(as Burgoon's patent teaches) is determined by the crystal
current, which has to overcome the shot noise of the grounded
base buffer.  The 10811 uses 1 mA RMS crystal current.  You
can turn this up and get even better phase noise, but then
you might degrade the stability of the crystal.  The stock
10811 has an output circuit that degrades the phase noise.
There are various reasons for why this was done including
backward compatibility with the 10544.  Few, if any, HP
instruments would actually benefit from the extremely low
phase noise.  The 10816 was different, since it was meant
to be sold as a component, not used in an HP instrument,
and we could advertise the spec.  Unfortunately, the 10816
project was cancelled by new management after the pilot
run.

BTW, Rob Burgoon, one of the designers of the HP 10811,
is going to retire from Agilent this month.

Rick Karlquist N6RK

Tom Van Baak wrote:
>> For what it's worth, the Wenzel 5 and 10 MHz ULN oscillators are
>> generally considered to be about the lowest noise oscillators
>> commercially available.  They really shine in their noise floor.
>> There's actually (at least) one 5MHz oscillator with a better 1Hz offset
>> spec -- the Oscilloquartz 8607-08 BVA at -130 dBc/Hz, though its noise
>> floor at about -160 dBc/Hz is nothing like the Wenzel's.
>>
>> Here's some data on the Wenzel units from their web site:
>>
>> 5 MHz 10 MHz
>> 1 Hz -120 -105
>> 10 Hz -150 -135
>> 100 Hz -170 -160
>> 1 kHz -176 -173
>> 10 kHz -176 -175
> 
> John,
> 
> Good timing; yesterday, John Miles was over here to test some ULN.
> Here's a Wenzel ULN 5 MHz against a ULN 10 MHz.
> http://www.leapsecond.com/museum/wenzel-uln/uln5-uln10.gif
> (these are relative measurements; absolute would be ~ 3 dB better)
> 
> Also, for those interested, two 8607-08 BVA against each other:
> http://www.leapsecond.com/museum/osa8607/8607-8607.gif
> 
> /tvb
> 
> 
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Re: [time-nuts] xtal oscillator phase noise

[John Miles]

There isnt any; that's not a correct assertion for crystal oscillators in
the general case.

The math associated with multiplying or dividing a frequency is pretty
straightforward.  If an input edge is N picoseconds late due to jitter, the
corresponding output edge is also going to be N picoseconds late within the
bandwidth of the device.

So it's easy to see how phase noise in dBc/Hz is related to the percentage
of one cycle that a given edge is early or late.  Double the duration of a
cycle, and the effect of a constant jitter deviation is halved, or reduced
by 6 dB by the usual 20*log(N) amplitude rule.  Halve the duration of a
cycle, and the effect of the jitter is doubled.

Crystal oscillators do not behave anything like dividers or multipliers,
unless they have dividers or multipliers built in.  Only the >160 MHz Wenzel
oscillators use built-in mulipliers, I believe, and none of them use
dividers unless you order one explicitly as a separate part.

Higher-frequency crystal oscillators are generally cleaner at offsets beyond
a few kHz.  Only at close-in offsets do the 5 MHz ULNs have an advantage
over the 10 MHz ones, and there are no hard-and-fast 6-dB relationships as a
rule.

-- john, KE5FX (got a lot more stuff to post, but it's going to take awhile
to get it together...)

> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Behalf Of Tom Van Baak
> Sent: Tuesday, January 01, 2008 11:22 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] xtal oscillator phase noise
>
>
> > Tom -
> >
> > Nice data. It really confirms what I initially posted. Your measurements
> > were at 5 MHz, so, the expected number at 10 MHz would be 6 dB
> worse. The
> > -155 dBc/Hz number quoted by memory from me then was not that
> far of at all.
> > - Mike
>
> Hi Mike,
>
> What's the math behind why an equivalently good 10 MHz
> reference is always(?) 6 dB above a 5 MHz reference?
>
> /tvb
>


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Re: [time-nuts] xtal oscillator phase noise

[Mike Feher]

Tom -

Sorry - I am not smart enough to answer that, other than from the experience
I had with the vendors. - Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Tom Van Baak
Sent: Tuesday, January 01, 2008 2:22 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] xtal oscillator phase noise

> Tom -
> 
> Nice data. It really confirms what I initially posted. Your measurements
> were at 5 MHz, so, the expected number at 10 MHz would be 6 dB worse. The
> -155 dBc/Hz number quoted by memory from me then was not that far of at
all.
> - Mike

Hi Mike,

What's the math behind why an equivalently good 10 MHz
reference is always(?) 6 dB above a 5 MHz reference?

/tvb


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Re: [time-nuts] xtal oscillator phase noise

[Mike Feher]

BTW, I remember when I was on a program and the initial oscillator was
specified at 5 MHz. When we changed it to 10 MHz, all of the vendors wanted
a 6 dB allowance on PN. - Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Mike Feher
Sent: Tuesday, January 01, 2008 2:12 PM
To: 'Tom Van Baak'; 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] xtal oscillator phase noise

Tom -

Nice data. It really confirms what I initially posted. Your measurements
were at 5 MHz, so, the expected number at 10 MHz would be 6 dB worse. The
-155 dBc/Hz number quoted by memory from me then was not that far of at all.
- Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Tom Van Baak
Sent: Tuesday, January 01, 2008 2:02 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise

> For what it's worth, the Wenzel 5 and 10 MHz ULN oscillators are
> generally considered to be about the lowest noise oscillators
> commercially available.  They really shine in their noise floor.
> There's actually (at least) one 5MHz oscillator with a better 1Hz offset
> spec -- the Oscilloquartz 8607-08 BVA at -130 dBc/Hz, though its noise
> floor at about -160 dBc/Hz is nothing like the Wenzel's.
>
> Here's some data on the Wenzel units from their web site:
> 
> 5 MHz 10 MHz
> 1 Hz -120 -105
> 10 Hz -150 -135
> 100 Hz -170 -160
> 1 kHz -176 -173
> 10 kHz -176 -175

John,

Good timing; yesterday, John Miles was over here to test some ULN.
Here's a Wenzel ULN 5 MHz against a ULN 10 MHz.
http://www.leapsecond.com/museum/wenzel-uln/uln5-uln10.gif
(these are relative measurements; absolute would be ~ 3 dB better)

Also, for those interested, two 8607-08 BVA against each other:
http://www.leapsecond.com/museum/osa8607/8607-8607.gif

/tvb


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Re: [time-nuts] xtal oscillator phase noise

[Tom Van Baak]

> Tom -
> 
> Nice data. It really confirms what I initially posted. Your measurements
> were at 5 MHz, so, the expected number at 10 MHz would be 6 dB worse. The
> -155 dBc/Hz number quoted by memory from me then was not that far of at all.
> - Mike

Hi Mike,

What's the math behind why an equivalently good 10 MHz
reference is always(?) 6 dB above a 5 MHz reference?

/tvb


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Re: [time-nuts] xtal oscillator phase noise

[Mike Feher]

Tom -

Nice data. It really confirms what I initially posted. Your measurements
were at 5 MHz, so, the expected number at 10 MHz would be 6 dB worse. The
-155 dBc/Hz number quoted by memory from me then was not that far of at all.
- Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Tom Van Baak
Sent: Tuesday, January 01, 2008 2:02 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise

> For what it's worth, the Wenzel 5 and 10 MHz ULN oscillators are
> generally considered to be about the lowest noise oscillators
> commercially available.  They really shine in their noise floor.
> There's actually (at least) one 5MHz oscillator with a better 1Hz offset
> spec -- the Oscilloquartz 8607-08 BVA at -130 dBc/Hz, though its noise
> floor at about -160 dBc/Hz is nothing like the Wenzel's.
>
> Here's some data on the Wenzel units from their web site:
> 
> 5 MHz 10 MHz
> 1 Hz -120 -105
> 10 Hz -150 -135
> 100 Hz -170 -160
> 1 kHz -176 -173
> 10 kHz -176 -175

John,

Good timing; yesterday, John Miles was over here to test some ULN.
Here's a Wenzel ULN 5 MHz against a ULN 10 MHz.
http://www.leapsecond.com/museum/wenzel-uln/uln5-uln10.gif
(these are relative measurements; absolute would be ~ 3 dB better)

Also, for those interested, two 8607-08 BVA against each other:
http://www.leapsecond.com/museum/osa8607/8607-8607.gif

/tvb


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Re: [time-nuts] xtal oscillator phase noise

[Tom Van Baak]

> For what it's worth, the Wenzel 5 and 10 MHz ULN oscillators are
> generally considered to be about the lowest noise oscillators
> commercially available.  They really shine in their noise floor.
> There's actually (at least) one 5MHz oscillator with a better 1Hz offset
> spec -- the Oscilloquartz 8607-08 BVA at -130 dBc/Hz, though its noise
> floor at about -160 dBc/Hz is nothing like the Wenzel's.
>
> Here's some data on the Wenzel units from their web site:
> 
> 5 MHz 10 MHz
> 1 Hz -120 -105
> 10 Hz -150 -135
> 100 Hz -170 -160
> 1 kHz -176 -173
> 10 kHz -176 -175

John,

Good timing; yesterday, John Miles was over here to test some ULN.
Here's a Wenzel ULN 5 MHz against a ULN 10 MHz.
http://www.leapsecond.com/museum/wenzel-uln/uln5-uln10.gif
(these are relative measurements; absolute would be ~ 3 dB better)

Also, for those interested, two 8607-08 BVA against each other:
http://www.leapsecond.com/museum/osa8607/8607-8607.gif

/tvb


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Re: [time-nuts] xtal oscillator phase noise

[John Ackermann N8UR]

Mike Feher said the following on 01/01/2008 09:47 AM:
> Yes, that is what I figured regarding the 12V. For me, it has more or less
> been a rule of thumb, but, I think at 10 MHz the best you could do, due to Q
> and transistor noise and gain, was about - 155 dBc/Hz at about 100 Hz from
> the carrier. I do not recall from your earlier post what you are actually
> measuring. I would think anything close to - 150 dBc/Hz would be very good.
> That is of course if you can even measure it at its fundamental frequency. -
> Mike

For what it's worth, the Wenzel 5 and 10 MHz ULN oscillators are
generally considered to be about the lowest noise oscillators
commercially available.  They really shine in their noise floor.
There's actually (at least) one 5MHz oscillator with a better 1Hz offset
spec -- the Oscilloquartz 8607-08 BVA at -130 dBc/Hz, though its noise
floor at about -160 dBc/Hz is nothing like the Wenzel's.

Here's some data on the Wenzel units from their web site:

5 MHz   10 MHz
1 Hz-120-105
10 Hz   -150-135
100 Hz  -170-160
1 kHz   -176-173
10 kHz  -176-175

(I recall having seen some 10 MHz specs on the web site that were a
couple of dB better than shown here, but these are what I could find
today for the "BlueTop ULN" which is their top of the line unit.)

John



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Re: [time-nuts] xtal oscillator phase noise

[Mike Feher]

Yes, that is what I figured regarding the 12V. For me, it has more or less
been a rule of thumb, but, I think at 10 MHz the best you could do, due to Q
and transistor noise and gain, was about - 155 dBc/Hz at about 100 Hz from
the carrier. I do not recall from your earlier post what you are actually
measuring. I would think anything close to - 150 dBc/Hz would be very good.
That is of course if you can even measure it at its fundamental frequency. -
Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Henk ten Pierick
Sent: Tuesday, January 01, 2008 9:20 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise

On Jan 1, 2008, at 14:13, Mike Feher wrote:

> The emitter follower should have a very low output impedance, so, I  
> would
> not be too concerned about it's driving capabilities. If you must  
> have 50
> ohms, well, then just connect a 47 ohm resistor after the 1 nf  
> capacitor and
> measure it there, without U1.

Yes

> The confusing thing about the ADR455 is that
> above, on the schematic, you claimed you derived the 12V from the  
> ADR455. I
> am not familiar with it, but, in that case, how did you get the 12  
> V from
> the 5 volt reference? - Mike

Sorry for the confusion. The 12 volt is derived from the 5 volt  
reference by a simple circuit, the usual series regulator build with  
discrete transistors. It will add some noise to the noise of the ADR455.

> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
>
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:time-nuts- 
> [EMAIL PROTECTED] On
> Behalf Of Henk ten Pierick
> Sent: Tuesday, January 01, 2008 8:03 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] xtal oscillator phase noise
>
> On Jan 1, 2008, at 13:42, Mike Feher wrote:
>
>> Henk -
>>
>> Did you try to measure the PN out of the oscillator directly
>> without the
>> buffer amp (U1)?
>
> No, but I will do it. I have to find a way, the emitter follower is
> not expected to drive 50 ohm.
>
>> Also, what is the voltage from V1? Is it also 12V?
>
> The ADR455 is a 5volt reference.
>
>> HNY -
>
> Same to you all.
>
> Henk
>
>> Mike
>>
>>
>>
>> Mike B. Feher, N4FS
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960
>>
>>
>> -Original Message-----
>> From: [EMAIL PROTECTED] [mailto:time-nuts-
>> [EMAIL PROTECTED] On
>> Behalf Of Henk ten Pierick
>> Sent: Tuesday, January 01, 2008 7:25 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] xtal oscillator phase noise
>>
>>
>> On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:
>>
>>> Henk
>>>
>>> The 30dB/decade phase noise slope could be the result of the
>>> effect of
>>> low pass filtering a power supply or reference source that has
>>> significant flicker noise.
>>
>> The reference used is an ADR455. I have not seen references
>> significant better. Suggestions?
>>
>>> Lack of local RF feedback and /or high dc gain from base to
>>> collector in
>>> BJT buffer stages can produce significant flicker phase noise.
>>
>> I have now doubled the dc voltage for the oscillating transistor for
>> the reduction of junction capacitances. It had no result on phase
>> noise.
>>
>> Is low hfe better for phase noise?
>>
>> Henk
>>
>> ___
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>
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Re: [time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

On Jan 1, 2008, at 14:13, Mike Feher wrote:

> The emitter follower should have a very low output impedance, so, I  
> would
> not be too concerned about it's driving capabilities. If you must  
> have 50
> ohms, well, then just connect a 47 ohm resistor after the 1 nf  
> capacitor and
> measure it there, without U1.

Yes

> The confusing thing about the ADR455 is that
> above, on the schematic, you claimed you derived the 12V from the  
> ADR455. I
> am not familiar with it, but, in that case, how did you get the 12  
> V from
> the 5 volt reference? - Mike

Sorry for the confusion. The 12 volt is derived from the 5 volt  
reference by a simple circuit, the usual series regulator build with  
discrete transistors. It will add some noise to the noise of the ADR455.

> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
>
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:time-nuts- 
> [EMAIL PROTECTED] On
> Behalf Of Henk ten Pierick
> Sent: Tuesday, January 01, 2008 8:03 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] xtal oscillator phase noise
>
> On Jan 1, 2008, at 13:42, Mike Feher wrote:
>
>> Henk -
>>
>> Did you try to measure the PN out of the oscillator directly
>> without the
>> buffer amp (U1)?
>
> No, but I will do it. I have to find a way, the emitter follower is
> not expected to drive 50 ohm.
>
>> Also, what is the voltage from V1? Is it also 12V?
>
> The ADR455 is a 5volt reference.
>
>> HNY -
>
> Same to you all.
>
> Henk
>
>> Mike
>>
>>
>>
>> Mike B. Feher, N4FS
>> 89 Arnold Blvd.
>> Howell, NJ, 07731
>> 732-886-5960
>>
>>
>> -Original Message-----
>> From: [EMAIL PROTECTED] [mailto:time-nuts-
>> [EMAIL PROTECTED] On
>> Behalf Of Henk ten Pierick
>> Sent: Tuesday, January 01, 2008 7:25 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] xtal oscillator phase noise
>>
>>
>> On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:
>>
>>> Henk
>>>
>>> The 30dB/decade phase noise slope could be the result of the
>>> effect of
>>> low pass filtering a power supply or reference source that has
>>> significant flicker noise.
>>
>> The reference used is an ADR455. I have not seen references
>> significant better. Suggestions?
>>
>>> Lack of local RF feedback and /or high dc gain from base to
>>> collector in
>>> BJT buffer stages can produce significant flicker phase noise.
>>
>> I have now doubled the dc voltage for the oscillating transistor for
>> the reduction of junction capacitances. It had no result on phase
>> noise.
>>
>> Is low hfe better for phase noise?
>>
>> Henk
>>
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
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>> time-nuts
>> and follow the instructions there.
>
>
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Re: [time-nuts] xtal oscillator phase noise

[Mike Feher]

The emitter follower should have a very low output impedance, so, I would
not be too concerned about it's driving capabilities. If you must have 50
ohms, well, then just connect a 47 ohm resistor after the 1 nf capacitor and
measure it there, without U1. The confusing thing about the ADR455 is that
above, on the schematic, you claimed you derived the 12V from the ADR455. I
am not familiar with it, but, in that case, how did you get the 12 V from
the 5 volt reference? - Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 

-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Henk ten Pierick
Sent: Tuesday, January 01, 2008 8:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise

On Jan 1, 2008, at 13:42, Mike Feher wrote:

> Henk -
>
> Did you try to measure the PN out of the oscillator directly  
> without the
> buffer amp (U1)?

No, but I will do it. I have to find a way, the emitter follower is  
not expected to drive 50 ohm.

> Also, what is the voltage from V1? Is it also 12V?

The ADR455 is a 5volt reference.

> HNY -

Same to you all.

Henk

> Mike
>
>
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:time-nuts- 
> [EMAIL PROTECTED] On
> Behalf Of Henk ten Pierick
> Sent: Tuesday, January 01, 2008 7:25 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] xtal oscillator phase noise
>
>
> On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:
>
>> Henk
>>
>> The 30dB/decade phase noise slope could be the result of the  
>> effect of
>> low pass filtering a power supply or reference source that has
>> significant flicker noise.
>
> The reference used is an ADR455. I have not seen references
> significant better. Suggestions?
>
>> Lack of local RF feedback and /or high dc gain from base to
>> collector in
>> BJT buffer stages can produce significant flicker phase noise.
>
> I have now doubled the dc voltage for the oscillating transistor for
> the reduction of junction capacitances. It had no result on phase  
> noise.
>
> Is low hfe better for phase noise?
>
> Henk
>
> ___
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Re: [time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

On Jan 1, 2008, at 13:42, Mike Feher wrote:

> Henk -
>
> Did you try to measure the PN out of the oscillator directly  
> without the
> buffer amp (U1)?

No, but I will do it. I have to find a way, the emitter follower is  
not expected to drive 50 ohm.

> Also, what is the voltage from V1? Is it also 12V?

The ADR455 is a 5volt reference.

> HNY -

Same to you all.

Henk

> Mike
>
>
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:time-nuts- 
> [EMAIL PROTECTED] On
> Behalf Of Henk ten Pierick
> Sent: Tuesday, January 01, 2008 7:25 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] xtal oscillator phase noise
>
>
> On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:
>
>> Henk
>>
>> The 30dB/decade phase noise slope could be the result of the  
>> effect of
>> low pass filtering a power supply or reference source that has
>> significant flicker noise.
>
> The reference used is an ADR455. I have not seen references
> significant better. Suggestions?
>
>> Lack of local RF feedback and /or high dc gain from base to
>> collector in
>> BJT buffer stages can produce significant flicker phase noise.
>
> I have now doubled the dc voltage for the oscillating transistor for
> the reduction of junction capacitances. It had no result on phase  
> noise.
>
> Is low hfe better for phase noise?
>
> Henk
>
> ___
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> To unsubscribe, go to
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>
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Re: [time-nuts] xtal oscillator phase noise

[Mike Feher]

Henk -

Did you try to measure the PN out of the oscillator directly without the
buffer amp (U1)? Also, what is the voltage from V1? Is it also 12V? HNY -
Mike

 
 
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
 
 
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Henk ten Pierick
Sent: Tuesday, January 01, 2008 7:25 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] xtal oscillator phase noise


On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:

> Henk
>
> The 30dB/decade phase noise slope could be the result of the effect of
> low pass filtering a power supply or reference source that has
> significant flicker noise.

The reference used is an ADR455. I have not seen references  
significant better. Suggestions?

> Lack of local RF feedback and /or high dc gain from base to  
> collector in
> BJT buffer stages can produce significant flicker phase noise.

I have now doubled the dc voltage for the oscillating transistor for  
the reduction of junction capacitances. It had no result on phase noise.

Is low hfe better for phase noise?

Henk

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Re: [time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

On Dec 30, 2007, at 19:03, Grant Hodgson wrote:

> Henk
>
> Two things will dominate if you want such a low phase noise spec.:-  
> the
>   loaded Q of the oscillator circuit, and the flicker corner frequency
> of the sustaining amplifier transistor.  To get a high loaded Q you  
> need
> a crystal with a high unloaded Q - maybe 100 000 or more - this isn't
> difficult to achieve from a good crystal manufacturer, but you can't
> expect any old crystal to work.  And the rest of the oscillator  
> circuit
> should not load the crystal too much, otherwise the loaded Q, and thus
> phase noise, will suffer.  Good crystal manufacturers will provide the
> necessary measurements of series resistance, motional inductance (or
> capacitance, or unloaded Q - doesn't matter which) and static
> capacitance.  Lesser crystal manufacturers - don't.

It showed to be very difficult to come lower than what I have now. If  
can be the crystal. How can I decide?

> Also the flicker corner frequency of the transistor needs to be as low
> as possible.  Generally speaking, at offsets below the flicker corner
> frequency you will get 30dB/decade, above the flicker corner frequency
> you should get 20dB/decade, or flat, depending on the level of the  
> phase
> noise floor.  If you can find a transistor with a lower corner
> frequency, the flicker noise will be reduced.  In fact, this is one of
> the dominant parameters when choosing a transistor as an oscillator -
> any old transistor can be made to oscillate, but to do so with a low
> flicker corner frequency is not so easy, and the corner frequency is
> usually a function of bias current.

I used the BC375 for the low Rbb' and assume that the noise corner  
must be low as a result of that. Is this not true?

> At 11MHz, most crystal oscillators use parallel resonant crystals,
> although some are series resonant, such as the excellent Driscoll
> oscillator which is capable of the performance you desire with a
> suitable crystal.

I was aware that most lower frequency circuits are parallel resonant.  
I used series in class A because I thought is was better, it is  
easier to use the current though the xtal. Is there a fundamental  
difference between parallel ore series w.r.t performance?

> Then you have the added problem of the FSUP.  It's a superb  
> instrument,
> but it has it's limitations.  The FSUP data sheet states a phase noise
> spec. of -130dBc at 10Hz offset for a 10MHz signal, which gives a
> resulting sensitivity of -127dBc - 3dB worse than what you are  
> trying to
> achieve.  You would need option B60 (cross correlation) to  
> significantly
> reduce the effect of the internal source by (say) 15db or so.

I do normally not have access to a FSUP but borrowed the instrument  
for two weeks. To my luck it has the B60 option and I used this of  
coarse. There must be a reason for my employer to buy this fantastic  
tool.

Henk


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Re: [time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

On Dec 30, 2007, at 3:42, Bruce Griffiths wrote:

> Henk
>
> The 30dB/decade phase noise slope could be the result of the effect of
> low pass filtering a power supply or reference source that has
> significant flicker noise.

The reference used is an ADR455. I have not seen references  
significant better. Suggestions?

> Lack of local RF feedback and /or high dc gain from base to  
> collector in
> BJT buffer stages can produce significant flicker phase noise.

I have now doubled the dc voltage for the oscillating transistor for  
the reduction of junction capacitances. It had no result on phase noise.

Is low hfe better for phase noise?

Henk

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Re: [time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

On Dec 30, 2007, at 0:03, Bruce Griffiths wrote:


Henk ten Pierick wrote:

Hello,

Some questions on xtal oscillator phase noise.



Henk

A circuit diagram for the oscillator is required before intelligent
comment about changes can be made.


Bruce,

1.  Best wishes.

2. It has taken some time but here is the schematic.

Henk



seriesOscillator.pdf
Description: Adobe PDF document
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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Don Collie wrote:
> Bruce, do you get out much?Don.
> - Original Message - 
>   
Don

I do give at least one public talk a month.
Also have done such things as attempting to measure the wavefont
distortion of a telescope using very little equipment.
The oft sited eyeball star testing techniques arent very effective with
larger telescopes when the seeing is poor (most of the time in Kirikiriroa).
Those that say you can Ronchi test or Foucault test a telescope on the
stars by eye are dreaming, an exposure of 30 sec or more is usually
necessary to average out the effects of air currents etc.
Have also found that the interferometric version of the Hartmann test is
easy and relatively inexpensive to do.

I also do some optical design for a diversion.

Bruce

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Re: [time-nuts] xtal oscillator phase noise

[Don Collie]

Bruce, do you get out much?Don.
- Original Message - 
From: "Bruce Griffiths" <[EMAIL PROTECTED]>
To: "Discussion of precise time and frequency measurement" 

Sent: Sunday, December 30, 2007 3:42 PM
Subject: Re: [time-nuts] xtal oscillator phase noise


> Henk
>
> The 30dB/decade phase noise slope could be the result of the effect of
> low pass filtering a power supply or reference source that has
> significant flicker noise.
> Lack of local RF feedback and /or high dc gain from base to collector in
> BJT buffer stages can produce significant flicker phase noise.
>
> Bruce
>
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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Grant Hodgson wrote:
> Henk
>
> Two things will dominate if you want such a low phase noise spec.:- the 
>   loaded Q of the oscillator circuit, and the flicker corner frequency 
> of the sustaining amplifier transistor.  To get a high loaded Q you need 
> a crystal with a high unloaded Q - maybe 100 000 or more - this isn't 
> difficult to achieve from a good crystal manufacturer, but you can't 
> expect any old crystal to work.  And the rest of the oscillator circuit 
> should not load the crystal too much, otherwise the loaded Q, and thus 
> phase noise, will suffer.  Good crystal manufacturers will provide the 
> necessary measurements of series resistance, motional inductance (or 
> capacitance, or unloaded Q - doesn't matter which) and static 
> capacitance.  Lesser crystal manufacturers - don't.
>
>   
A Q of 100,000 at 10MHz produces a Leeson effect phase noise corner of
100Hz
(below which the phase noise slope is 20dB/decade).
This makes it much harder to achieve the desired phase noise at 10Hz
than a crystal with a Q of 1,000,000.
> Also the flicker corner frequency of the transistor needs to be as low 
> as possible.  Generally speaking, at offsets below the flicker corner 
> frequency you will get 30dB/decade, above the flicker corner frequency 
> you should get 20dB/decade, or flat, depending on the level of the phase 
> noise floor.  If you can find a transistor with a lower corner 
> frequency, the flicker noise will be reduced.  In fact, this is one of 
> the dominant parameters when choosing a transistor as an oscillator - 
> any old transistor can be made to oscillate, but to do so with a low 
> flicker corner frequency is not so easy, and the corner frequency is 
> usually a function of bias current.
>
>   
Its not quite that simple, the flicker phase modulation depends on the
voltage and/or
current dependence of the various transistor capacitances etc and the
consequent phase
modulation produced by low frequency noise currents flowing through the
transistor
or low frequency noise voltages developed across such capacitances.
Simply choosing
a low flicker noise transistor without taking its collector base
capacitance, emitter base
capacitance, etc into account is unlikely to reduce the flicker phase noise.
Reducing the dc gain from the base to the collector and ensuring that
the emitter current
low frequency noise is low is likely to be more effective.
Increasing the collector base voltage will reduce the collector base
capacitance and its voltage dependence.
The oscillator power supply noise can also modulate the transistor
collector current and thus increase the phase noise.
> At 11MHz, most crystal oscillators use parallel resonant crystals, 
> although some are series resonant, such as the excellent Driscoll 
> oscillator which is capable of the performance you desire with a 
> suitable crystal.
>
> Then you have the added problem of the FSUP.  It's a superb instrument, 
> but it has it's limitations.  The FSUP data sheet states a phase noise 
> spec. of -130dBc at 10Hz offset for a 10MHz signal, which gives a 
> resulting sensitivity of -127dBc - 3dB worse than what you are trying to 
> achieve.  You would need option B60 (cross correlation) to significantly 
> reduce the effect of the internal source by (say) 15db or so.
>
> regards
>
> Grant
>
>   
The measured oscillator phase noise floor seems a little high for a
modern low phase noise design.
If the oscillator uses varicap diodes to adjust the oscillation
frequency, these can contribute
significantly to the phase noise especially if their tuning range is large.
Testing the oscillator without varicaps (if possible) and with lower
noise supplies may also be useful.
Failing removal of such varicaps reconfiguring the EFC so that the
varicap has a much smaller tuning range
(supplemented by a manual trimmer) may be useful in reducing the phase
noise contribution of the EFC circuit.
Use a capacitive attenuator to reduce the EFC range, not a resistive
attenuator on the EFC control voltage.

Bruce

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Re: [time-nuts] xtal oscillator phase noise

[Rick Karlquist]

AFAIK, in a crystal oscillator specifically (not oscillators
in general), the oscillator transistor has almost nothing to
do with either close in or far out phase noise.  The close in
phase noise is typically limited by the crystal's intrinsic
noise and the far out phase noise is limited by the buffer
amplifier, assuming you take the output through the crystal
as is done in the 10811.  Certainly in the case of the 10811,
the oscillator transistor (a selected 2N5179) is not a player
in terms of noise.  BTW, the selection is based on startup
issues and has nothing to do with noise.  The buffer amplifier
transistor contributes shot noise, however this is determined
by physics, not choice of transistor.  So again, choice of
transistor is irrelevent for noise purposes.  You do have to
worry about distortion in the buffer amplifier that can
upconvert 1/f noise.  This can possibly require transistors
with constant beta vs collector current, depending on the
circuit design.

Rick Karlquist N6RK


Grant Hodgson wrote:
> Henk
>
> Two things will dominate if you want such a low phase noise spec.:- the
>   loaded Q of the oscillator circuit, and the flicker corner frequency
> of the sustaining amplifier transistor.  To get a high loaded Q you need
> a crystal with a high unloaded Q - maybe 100 000 or more - this isn't
> difficult to achieve from a good crystal manufacturer, but you can't
> expect any old crystal to work.  And the rest of the oscillator circuit
> should not load the crystal too much, otherwise the loaded Q, and thus
> phase noise, will suffer.  Good crystal manufacturers will provide the
> necessary measurements of series resistance, motional inductance (or
> capacitance, or unloaded Q - doesn't matter which) and static
> capacitance.  Lesser crystal manufacturers - don't.
>
> Also the flicker corner frequency of the transistor needs to be as low
> as possible.  Generally speaking, at offsets below the flicker corner
> frequency you will get 30dB/decade, above the flicker corner frequency
> you should get 20dB/decade, or flat, depending on the level of the phase
> noise floor.  If you can find a transistor with a lower corner
> frequency, the flicker noise will be reduced.  In fact, this is one of
> the dominant parameters when choosing a transistor as an oscillator -
> any old transistor can be made to oscillate, but to do so with a low
> flicker corner frequency is not so easy, and the corner frequency is
> usually a function of bias current.
>
> At 11MHz, most crystal oscillators use parallel resonant crystals,
> although some are series resonant, such as the excellent Driscoll
> oscillator which is capable of the performance you desire with a
> suitable crystal.
>
> Then you have the added problem of the FSUP.  It's a superb instrument,
> but it has it's limitations.  The FSUP data sheet states a phase noise
> spec. of -130dBc at 10Hz offset for a 10MHz signal, which gives a
> resulting sensitivity of -127dBc - 3dB worse than what you are trying to
> achieve.  You would need option B60 (cross correlation) to significantly
> reduce the effect of the internal source by (say) 15db or so.
>
> regards
>
> Grant
>
> Henk wrote :-
> Hello,
>
> Some questions on xtal oscillator phase noise. Attached the
> measurement result of my series resonant xtal oscillator.
> It is a class A, ibias 5 mA, Ixtal 1 mArms. Transistor selected for
> low Rbb' 20 Ohm, Ft 100MHz. Reference voltage 5V from an ADR445,
> filtered with 10uF folie cap. Phase noise target -130dBc at 10Hz.
>
> 1. Is series resonant better or easier to engineer than parallel
> resonant?
>
> 2. Where should I have 20 dB/decade and where 30 B/decade?
>
> 3. Some suggestions for the next 25dB?
>
> 4. Is there more to learn from the attached picture?
>
> regards,
>
> Henk
>
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>
>



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Re: [time-nuts] xtal oscillator phase noise

[Grant Hodgson]

Henk

Two things will dominate if you want such a low phase noise spec.:- the 
  loaded Q of the oscillator circuit, and the flicker corner frequency 
of the sustaining amplifier transistor.  To get a high loaded Q you need 
a crystal with a high unloaded Q - maybe 100 000 or more - this isn't 
difficult to achieve from a good crystal manufacturer, but you can't 
expect any old crystal to work.  And the rest of the oscillator circuit 
should not load the crystal too much, otherwise the loaded Q, and thus 
phase noise, will suffer.  Good crystal manufacturers will provide the 
necessary measurements of series resistance, motional inductance (or 
capacitance, or unloaded Q - doesn't matter which) and static 
capacitance.  Lesser crystal manufacturers - don't.

Also the flicker corner frequency of the transistor needs to be as low 
as possible.  Generally speaking, at offsets below the flicker corner 
frequency you will get 30dB/decade, above the flicker corner frequency 
you should get 20dB/decade, or flat, depending on the level of the phase 
noise floor.  If you can find a transistor with a lower corner 
frequency, the flicker noise will be reduced.  In fact, this is one of 
the dominant parameters when choosing a transistor as an oscillator - 
any old transistor can be made to oscillate, but to do so with a low 
flicker corner frequency is not so easy, and the corner frequency is 
usually a function of bias current.

At 11MHz, most crystal oscillators use parallel resonant crystals, 
although some are series resonant, such as the excellent Driscoll 
oscillator which is capable of the performance you desire with a 
suitable crystal.

Then you have the added problem of the FSUP.  It's a superb instrument, 
but it has it's limitations.  The FSUP data sheet states a phase noise 
spec. of -130dBc at 10Hz offset for a 10MHz signal, which gives a 
resulting sensitivity of -127dBc - 3dB worse than what you are trying to 
achieve.  You would need option B60 (cross correlation) to significantly 
reduce the effect of the internal source by (say) 15db or so.

regards

Grant

Henk wrote :-
Hello,

Some questions on xtal oscillator phase noise. Attached the
measurement result of my series resonant xtal oscillator.
It is a class A, ibias 5 mA, Ixtal 1 mArms. Transistor selected for
low Rbb' 20 Ohm, Ft 100MHz. Reference voltage 5V from an ADR445,
filtered with 10uF folie cap. Phase noise target -130dBc at 10Hz.

1. Is series resonant better or easier to engineer than parallel
resonant?

2. Where should I have 20 dB/decade and where 30 B/decade?

3. Some suggestions for the next 25dB?

4. Is there more to learn from the attached picture?

regards,

Henk

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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Henk

The 30dB/decade phase noise slope could be the result of the effect of
low pass filtering a power supply or reference source that has
significant flicker noise.
Lack of local RF feedback and /or high dc gain from base to collector in
BJT buffer stages can produce significant flicker phase noise.

Bruce

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Re: [time-nuts] xtal oscillator phase noise

[Bruce Griffiths]

Henk ten Pierick wrote:
> Hello,
>
> Some questions on xtal oscillator phase noise. Attached the
> measurement result of my series resonant xtal oscillator.
> It is a class A, ibias 5 mA, Ixtal 1 mArms. Transistor selected for
> low Rbb' 20 Ohm, Ft 100MHz. Reference voltage 5V from an ADR445,
> filtered with 10uF folie cap. Phase noise target -130dBc at 10Hz.
>
> 1. Is series resonant better or easier to engineer than parallel
> resonant?
>
> 2. Where should I have 20 dB/decade and where 30 B/decade?
>
> 3. Some suggestions for the next 25dB?
>
> 4. Is there more to learn from the attached picture?
>
> regards,
>
> Henk

Henk

A circuit diagram for the oscillator is required before intelligent
comment about changes can be made.
Either the crystal or the oscillator transistor may be limiting the
phase noise in the flicker region.
A different oscillator configuration may be better.


Bruce

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[time-nuts] xtal oscillator phase noise

[Henk ten Pierick]

Hello,

Some questions on xtal oscillator phase noise. Attached the  
measurement result of my series resonant xtal oscillator.
It is a class A, ibias 5 mA, Ixtal 1 mArms. Transistor selected for  
low Rbb' 20 Ohm, Ft 100MHz. Reference voltage 5V from an ADR445,  
filtered with 10uF folie cap. Phase noise target -130dBc at 10Hz.


1. Is series resonant better or easier to engineer than parallel  
resonant?


2. Where should I have 20 dB/decade and where 30 B/decade?

3. Some suggestions for the next 25dB?

4. Is there more to learn from the attached picture?

regards,

Henk

<>

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