Re: [time-nuts] distribution amp question + hp 59309A

[John Miles]

> What is the general feeling here about this issue?  I confess that if the amp
> output is transformer coupled, I see exactly zero benefit in a grounded
> connector as the feed from the amplifier.

This question comes up every so often.  It comes down to whether you want your 
test setup to look like a loop antenna or a dipole antenna.  Usually the loop 
is better if you're forced to accept one condition or the other.   You 
shouldn't break, lift, or otherwise mess with coax shields without a very good 
reason.  If you need a balanced connection, use a balanced medium.

Obviously if you're setting up a commercial 10base2 installation the rules are 
different. :)  But for sensitive work with low signal levels in coax, you will 
most often be better off if all of your gear looks like a series of monolithic 
metal bricks.   Ground loops are not the worst thing that can happen to a 
precision T measurement.  

-- john, KE5FX
Miles Design LLC


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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Charles Steinmetz]

Scott wrote:


Parasitic capacitance on the inverting terminal from routing and the
input capacitance of the opamp itself, adds another pole to your opamp's
loopgain, burning phase margin.

A small compensation cap across the top leg of your feedback divider, would
boost your phase margin.


Also, block out the ground plane on all layers under the inverting input 
and the traces leading to the feedback resistors, to minimize stray 
capacitance.


The OP mentioned that the peaking was greater at the outputs farther 
away from the input opamp (i.e., those with longer feed trace).  The 
trace inductance resonates with any stray capacitance.  Block out the 
ground planes under and adjacent to the feed trace.  It may also help to 
terminate the far end (not the near end) of the feed trace with 50-100 
ohms, and increase R109 to ~50 ohms.


Best regards,

Charles


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Re: [time-nuts] distribution amp question + hp 59309A

[Bob Stewart]

Walter said:
"Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten 
shelf  and looked at it, and was surprised to see such a poor primary time 
standard oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. 
It can accept an external standard, but it did feel odd for a device that is 
meant to provide coordinated system time to be so modestly executed.  it's like 
an uncorrected PC desktop clock." Doesn't this policy actually help prevent the 
"two clocks problem"?  If every piece of equipment has its own frequency 
standard, then how do you compare anything?  OTOH, if you buy one piece of 
equipment with a 10811 (or Rb or Cs or GPSDO) and use that to feed the rest, 
then even it's wrong, they're all wrong by the same amount.
Bob 

  From: walter shawlee 2 
 To: time-nuts@febo.com 
 Sent: Saturday, January 28, 2017 11:29 AM
 Subject: [time-nuts] distribution amp question + hp 59309A
   
I notice that in the distribution amp being discussed at the moment,
the BNC output connectors are grounded, and tied to the chassis,
which in turn has a grounded emi line filter. this seems like an unavoidable 
noise pathway to me.

I notice that some commercial amps are grounded, but more advanced and 
transformer coupled units have floating connectors. it makes the most sense to 
me to be floating, since this frees the return from line noise and spurious, 
and 
avoids the significant problem of shifted AC voltages on the return from 
distant 
units connected to the amp which are on other ac line circuits.

What is the general feeling here about this issue?  I confess that if the amp 
output is transformer coupled, I see exactly zero benefit in a grounded 
connector as the feed from the amplifier.

Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten 
shelf 
and looked at it, and was surprised to see such a poor primary time standard 
oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can 
accept an external standard, but it did feel odd for a device that is meant to 
provide coordinated system time to be so modestly executed.  it's like an 
uncorrected PC desktop clock.

This same issue pops up in many hp/agilent counters, signal generators and 
related objects. I have always been puzzled by the decision to make such 
marginal instruments that have time/frequency as their primary parameter, when 
so little additional effort would have dramatically improved them.  I do get 
the 
concept of an external standard reference, but it's a pretty weak argument for 
making a $5K generator or counter with poor performance.  Just curious to know 
everybody's thoughts on this.

all the best,
walter

-- 
Walter Shawlee 2, President
Sphere Research Corporation
3394 Sunnyside Rd.,  West Kelowna,  BC
V1Z 2V4  CANADA  Phone: (250) 769-1834
walt...@sphere.bc.ca
WS2: We're all in one boat, no matter how it looks to you.
Love is all you need. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

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Re: [time-nuts] distribution amp question + hp 59309A

[Tom Van Baak]

> Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten 
> shelf 
> and looked at it, and was surprised to see such a poor primary time standard 
> oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can 
> accept an external standard, but it did feel odd for a device that is meant 
> to 
> provide coordinated system time to be so modestly executed.  it's like an 
> uncorrected PC desktop clock.

Walter,

The hp 59503A was intended as a GPIB "system" time of day clock in the days 
before PC's had their own clocks, or before NTP or GPS existed. Imagine a 19" 
rack with 2 or 3 or 10 HP-IB instruments all on the same bus doing some complex 
experiment yet and no instrument knows the date or time-of-day that the data is 
collected, or maybe the controller needs to synchronize events across several 
instruments. Well, just add a 59503A and you're all set. It even has a battery 
backup option.

To their credit, and unlike a PC, there is an external frequency input, so you 
have control over the accuracy. It's a beautiful little instrument (lots of 
discussion in the archives).

/tvb

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Re: [time-nuts] distribution amp question + hp 59309A

[Bob Camp]

Hi

The gotcha with transformer coupled coax is keeping it terminated over a wide 
range of frequencies. If the coax is miss terminated
and the end of the cable is floating, you have a pretty good opportunity for 
noise to get into the system. Floating shields are also a 
pretty good way to get crosstalk. In many situations, isolation between outputs 
is a pretty big deal. 

Bob

> On Jan 28, 2017, at 12:29 PM, walter shawlee 2  wrote:
> 
> I notice that in the distribution amp being discussed at the moment,
> the BNC output connectors are grounded, and tied to the chassis,
> which in turn has a grounded emi line filter. this seems like an unavoidable 
> noise pathway to me.
> 
> I notice that some commercial amps are grounded, but more advanced and 
> transformer coupled units have floating connectors. it makes the most sense 
> to me to be floating, since this frees the return from line noise and 
> spurious, and avoids the significant problem of shifted AC voltages on the 
> return from distant units connected to the amp which are on other ac line 
> circuits.
> 
> What is the general feeling here about this issue?  I confess that if the amp 
> output is transformer coupled, I see exactly zero benefit in a grounded 
> connector as the feed from the amplifier.
> 
> Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten 
> shelf and looked at it, and was surprised to see such a poor primary time 
> standard oscillator inside, just a 1Mhz crystal using a cmos buffer 
> oscillator. It can accept an external standard, but it did feel odd for a 
> device that is meant to provide coordinated system time to be so modestly 
> executed.  it's like an uncorrected PC desktop clock.
> 
> This same issue pops up in many hp/agilent counters, signal generators and 
> related objects. I have always been puzzled by the decision to make such 
> marginal instruments that have time/frequency as their primary parameter, 
> when so little additional effort would have dramatically improved them.  I do 
> get the concept of an external standard reference, but it's a pretty weak 
> argument for making a $5K generator or counter with poor performance.  Just 
> curious to know everybody's thoughts on this.
> 
> all the best,
> walter
> 
> -- 
> Walter Shawlee 2, President
> Sphere Research Corporation
> 3394 Sunnyside Rd.,  West Kelowna,  BC
> V1Z 2V4  CANADA  Phone: (250) 769-1834
> walt...@sphere.bc.ca
> WS2: We're all in one boat, no matter how it looks to you.
> Love is all you need. (John Lennon)
> But, that doesn't mean other things don't come in handy. (WS2)
> 
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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Scott Stobbe]

Nice project. The gain peaking is more than likely from your high speed
opamp. Parasitic capacitance on the inverting terminal from routing and the
input capacitance of the opamp itself, adds another pole to your opamps
loopgain, burning phase margin.

A small compensation cap across the top leg of your feedback divider, would
boost your phase margin.

Actually, Jim Williams has a monster app note, N47 dedicated to high speed
amplifiers :)
On Sat, Jan 28, 2017 at 7:10 AM Anders Wallin 
wrote:

> Hi all,
> I've been tinkering with another distribution amplifier design and made
> some measurements earlier this week.
> The goal is roughly 1:8 fan-out, gain of 0 dB, for good quality (Cs, maser,
> OCXO) 5 or 10 MHz signals in the range of maybe +0 dBm to +15 dBm - in a 1U
> form-factor.
>
> Earlier I made an SMD version of the TADD-1 design [1] which showed about
> -156 dBc/Hz far-out phase-noise but was quite sensitive to external noise
> and required 12VDC power from a lead-acid battery as well as shielding in
> aluminium foil for a 'quiet' PN-spectrum.
> I then did some SPICE simulations [2] (never trust them without testing ;)
> which indicated ADA4899 would be a good op-amp. In practice the
> slew-rate/distortion was limiting and the AD4899 version didn't show better
> PN.
>
> This new version is inspired by looking inside a 6502[3] - and in the
> mean-time I also measured and Ettus Octoclock [4] - but its performance
> isn't so exciting..
>
> My current design is now here: https://goo.gl/photos/WB8fYd4jzba7nXH18
> So far my observations are:
> - phase noise around -162 dBc/Hz at 10 MHz
> - nice quiet PN-spectrum when unshielded and powered from lab-supplies
> - this probably means the supply-section with common-mode choke, BNX025
> filter and LT1963/LT3015 is working OK. I should probably build a
> 10Hz-100kHz LNA (e.g. [5]) to verify. I've used 2k@100MHz ferrites a lot
> and an RC-filter on all supply pins - maybe overkill?
> - an undesired feature is gain-peaking which increases from output ch1 to
> ch8, shown here: https://goo.gl/photos/6QkoKakSPDdT7Acj7
> I tried to improve it a bit by adding a 100pF cap at the start of the long
> trace that feeds the output stages, but some gain-peaking still remains:
> https://goo.gl/photos/qrkLzZ21ptcHxFsw6
> - reverse isolation around 120 dB
> - channel-to-channel isolation around 80 dB
> - at 10MHz 1dB compression between +14 and +15 dBm
> - IP3 perhaps +27dBm to +30 dBm.
>
> Any ideas on how to deal with the long 'feeder-trace' that seems to be the
> cause of the gain-peaking?
> Anyway if not used at 100MHz perhaps my next version will have reduced BW
> where the feeder-trace is not an issue..
> Another issue is that the voltage regulators get quite hot when fed at
> +/-12V and producing +/-6V. They should probably be positioned as far away
> from the input/output amps and thermally disconnected if possible. I have a
> +/-12V AC/DC brick on order - but a DIY linear PSU producing e.g. +/-8VDC
> for the regulators might be better.
>
> The picture gallery also shows a pulse distribution amp for 1PPS. It has an
> LT1711 comparator feeding an 74AC14 buffer with length-matched traces to
> 74AC04's at the outputs. So far my length-matching didn't give zero
> output-skew between the outputs - I see around 150-200ps skew which I tried
> to tune a bit with wires and 0R resistors - without very much success.. any
> ideas for improving this - or just leave it at 200ps skew?
>
> cheers,
> Anders
>
> [1]
>
> http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-first-tests/
> [2]
>
> http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-v2-simulations/
> [3]
>
> http://www.anderswallin.net/2016/02/symmetricom-6502-distribution-amplifier/
> [4]
> http://www.anderswallin.net/2016/09/ettus-octoclock-distribution-amplifier/
> [5] http://cds.linear.com/docs/en/application-note/an83f.pdf
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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Bob Camp]

Hi

The real question is: Do you have an application where < 100 ps matching 
matters? If so do you 
need to match both at the amplifier *and* at the ends of the cables? 

Other than a phased array radar, I can’t think of to many situations where the 
answer is yes …
Put another way, for the normal stuff we do, it is not a significant issue. If 
you know the offset
you can take it out in any calculations where it might matter. 

Bob

> On Jan 28, 2017, at 6:58 AM, Anders Wallin  
> wrote:
> 
> Hi all,
> I've been tinkering with another distribution amplifier design and made
> some measurements earlier this week.
> The goal is roughly 1:8 fan-out, gain of 0 dB, for good quality (Cs, maser,
> OCXO) 5 or 10 MHz signals in the range of maybe +0 dBm to +15 dBm - in a 1U
> form-factor.
> 
> Earlier I made an SMD version of the TADD-1 design [1] which showed about
> -156 dBc/Hz far-out phase-noise but was quite sensitive to external noise
> and required 12VDC power from a lead-acid battery as well as shielding in
> aluminium foil for a 'quiet' PN-spectrum.
> I then did some SPICE simulations [2] (never trust them without testing ;)
> which indicated ADA4899 would be a good op-amp. In practice the
> slew-rate/distortion was limiting and the AD4899 version didn't show better
> PN.
> 
> This new version is inspired by looking inside a 6502[3] - and in the
> mean-time I also measured and Ettus Octoclock [4] - but its performance
> isn't so exciting..
> 
> My current design is now here: https://goo.gl/photos/WB8fYd4jzba7nXH18
> So far my observations are:
> - phase noise around -162 dBc/Hz at 10 MHz
> - nice quiet PN-spectrum when unshielded and powered from lab-supplies
> - this probably means the supply-section with common-mode choke, BNX025
> filter and LT1963/LT3015 is working OK. I should probably build a
> 10Hz-100kHz LNA (e.g. [5]) to verify. I've used 2k@100MHz ferrites a lot
> and an RC-filter on all supply pins - maybe overkill?
> - an undesired feature is gain-peaking which increases from output ch1 to
> ch8, shown here: https://goo.gl/photos/6QkoKakSPDdT7Acj7
> I tried to improve it a bit by adding a 100pF cap at the start of the long
> trace that feeds the output stages, but some gain-peaking still remains:
> https://goo.gl/photos/qrkLzZ21ptcHxFsw6
> - reverse isolation around 120 dB
> - channel-to-channel isolation around 80 dB
> - at 10MHz 1dB compression between +14 and +15 dBm
> - IP3 perhaps +27dBm to +30 dBm.
> 
> Any ideas on how to deal with the long 'feeder-trace' that seems to be the
> cause of the gain-peaking?
> Anyway if not used at 100MHz perhaps my next version will have reduced BW
> where the feeder-trace is not an issue..
> Another issue is that the voltage regulators get quite hot when fed at
> +/-12V and producing +/-6V. They should probably be positioned as far away
> from the input/output amps and thermally disconnected if possible. I have a
> +/-12V AC/DC brick on order - but a DIY linear PSU producing e.g. +/-8VDC
> for the regulators might be better.
> 
> The picture gallery also shows a pulse distribution amp for 1PPS. It has an
> LT1711 comparator feeding an 74AC14 buffer with length-matched traces to
> 74AC04's at the outputs. So far my length-matching didn't give zero
> output-skew between the outputs - I see around 150-200ps skew which I tried
> to tune a bit with wires and 0R resistors - without very much success.. any
> ideas for improving this - or just leave it at 200ps skew?
> 
> cheers,
> Anders
> 
> [1]
> http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-first-tests/
> [2]
> http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-v2-simulations/
> [3]
> http://www.anderswallin.net/2016/02/symmetricom-6502-distribution-amplifier/
> [4]
> http://www.anderswallin.net/2016/09/ettus-octoclock-distribution-amplifier/
> [5] http://cds.linear.com/docs/en/application-note/an83f.pdf
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[time-nuts] distribution amp question + hp 59309A

[walter shawlee 2]

I notice that in the distribution amp being discussed at the moment,
the BNC output connectors are grounded, and tied to the chassis,
which in turn has a grounded emi line filter. this seems like an unavoidable 
noise pathway to me.


I notice that some commercial amps are grounded, but more advanced and 
transformer coupled units have floating connectors. it makes the most sense to 
me to be floating, since this frees the return from line noise and spurious, and 
avoids the significant problem of shifted AC voltages on the return from distant 
units connected to the amp which are on other ac line circuits.


What is the general feeling here about this issue?  I confess that if the amp 
output is transformer coupled, I see exactly zero benefit in a grounded 
connector as the feed from the amplifier.


Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten shelf 
and looked at it, and was surprised to see such a poor primary time standard 
oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can 
accept an external standard, but it did feel odd for a device that is meant to 
provide coordinated system time to be so modestly executed.  it's like an 
uncorrected PC desktop clock.


This same issue pops up in many hp/agilent counters, signal generators and 
related objects. I have always been puzzled by the decision to make such 
marginal instruments that have time/frequency as their primary parameter, when 
so little additional effort would have dramatically improved them.  I do get the 
concept of an external standard reference, but it's a pretty weak argument for 
making a $5K generator or counter with poor performance.  Just curious to know 
everybody's thoughts on this.


all the best,
walter

--
Walter Shawlee 2, President
Sphere Research Corporation
3394 Sunnyside Rd.,  West Kelowna,  BC
V1Z 2V4  CANADA  Phone: (250) 769-1834
walt...@sphere.bc.ca
WS2: We're all in one boat, no matter how it looks to you.
Love is all you need. (John Lennon)
But, that doesn't mean other things don't come in handy. (WS2)

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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Mattia Rizzi]

Hello,

>The picture gallery also shows a pulse distribution amp for 1PPS. It has an
LT1711 comparator feeding an 74AC14 buffer with length-matched traces to
74AC04's at the outputs. So far my length-matching didn't give zero
output-skew between the outputs - I see around 150-200ps skew which I tried
to tune a bit with wires and 0R resistors - without very much success.. any
ideas for improving this - or just leave it at 200ps skew?

It's not unexpected since you're using ICs not designated (process
variation tolerant) nor characterized for picoseconds output-to-output
skew.
Have you tried to use clock distribution components like 5PB1108? You could
use that to distribute the LT1711 output to the output stages
*independently*. You could use also 5PB1108 as output stage as well (but
this depends on your output voltage level), I got like >3V/ns on a 50ohm
with 6 outputs tied together. For fine alignment a variable capacitor (or
RC filter) at the output stage's input pin may do the job.

cheers,
Mattia


2017-01-28 12:58 GMT+01:00 Anders Wallin :

> Hi all,
> I've been tinkering with another distribution amplifier design and made
> some measurements earlier this week.
> The goal is roughly 1:8 fan-out, gain of 0 dB, for good quality (Cs, maser,
> OCXO) 5 or 10 MHz signals in the range of maybe +0 dBm to +15 dBm - in a 1U
> form-factor.
>
> Earlier I made an SMD version of the TADD-1 design [1] which showed about
> -156 dBc/Hz far-out phase-noise but was quite sensitive to external noise
> and required 12VDC power from a lead-acid battery as well as shielding in
> aluminium foil for a 'quiet' PN-spectrum.
> I then did some SPICE simulations [2] (never trust them without testing ;)
> which indicated ADA4899 would be a good op-amp. In practice the
> slew-rate/distortion was limiting and the AD4899 version didn't show better
> PN.
>
> This new version is inspired by looking inside a 6502[3] - and in the
> mean-time I also measured and Ettus Octoclock [4] - but its performance
> isn't so exciting..
>
> My current design is now here: https://goo.gl/photos/WB8fYd4jzba7nXH18
> So far my observations are:
> - phase noise around -162 dBc/Hz at 10 MHz
> - nice quiet PN-spectrum when unshielded and powered from lab-supplies
> - this probably means the supply-section with common-mode choke, BNX025
> filter and LT1963/LT3015 is working OK. I should probably build a
> 10Hz-100kHz LNA (e.g. [5]) to verify. I've used 2k@100MHz ferrites a lot
> and an RC-filter on all supply pins - maybe overkill?
> - an undesired feature is gain-peaking which increases from output ch1 to
> ch8, shown here: https://goo.gl/photos/6QkoKakSPDdT7Acj7
> I tried to improve it a bit by adding a 100pF cap at the start of the long
> trace that feeds the output stages, but some gain-peaking still remains:
> https://goo.gl/photos/qrkLzZ21ptcHxFsw6
> - reverse isolation around 120 dB
> - channel-to-channel isolation around 80 dB
> - at 10MHz 1dB compression between +14 and +15 dBm
> - IP3 perhaps +27dBm to +30 dBm.
>
> Any ideas on how to deal with the long 'feeder-trace' that seems to be the
> cause of the gain-peaking?
> Anyway if not used at 100MHz perhaps my next version will have reduced BW
> where the feeder-trace is not an issue..
> Another issue is that the voltage regulators get quite hot when fed at
> +/-12V and producing +/-6V. They should probably be positioned as far away
> from the input/output amps and thermally disconnected if possible. I have a
> +/-12V AC/DC brick on order - but a DIY linear PSU producing e.g. +/-8VDC
> for the regulators might be better.
>
> The picture gallery also shows a pulse distribution amp for 1PPS. It has an
> LT1711 comparator feeding an 74AC14 buffer with length-matched traces to
> 74AC04's at the outputs. So far my length-matching didn't give zero
> output-skew between the outputs - I see around 150-200ps skew which I tried
> to tune a bit with wires and 0R resistors - without very much success.. any
> ideas for improving this - or just leave it at 200ps skew?
>
> cheers,
> Anders
>
> [1]
> http://www.anderswallin.net/2015/12/frequency-
> distribution-amplifier-first-tests/
> [2]
> http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-v2-
> simulations/
> [3]
> http://www.anderswallin.net/2016/02/symmetricom-6502-
> distribution-amplifier/
> [4]
> http://www.anderswallin.net/2016/09/ettus-octoclock-
> distribution-amplifier/
> [5] http://cds.linear.com/docs/en/application-note/an83f.pdf
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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Hal Murray]

anders.e.e.wal...@gmail.com said:
> I see around 150-200ps skew which I tried to tune a bit with wires and 0R
> resistors - without very much success.. any ideas for improving this - or
> just leave it at 200ps skew?

I don't have the numbers handy, but that's ballpark of an inch of trace on a 
PCB.

Outer layers are slightly faster than inner layers.  Details depend on the 
materials.  Solder mask slows down the outer layer slightly and things like 
that.

-- 
These are my opinions.  I hate spam.



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[time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

[Anders Wallin]

Hi all,
I've been tinkering with another distribution amplifier design and made
some measurements earlier this week.
The goal is roughly 1:8 fan-out, gain of 0 dB, for good quality (Cs, maser,
OCXO) 5 or 10 MHz signals in the range of maybe +0 dBm to +15 dBm - in a 1U
form-factor.

Earlier I made an SMD version of the TADD-1 design [1] which showed about
-156 dBc/Hz far-out phase-noise but was quite sensitive to external noise
and required 12VDC power from a lead-acid battery as well as shielding in
aluminium foil for a 'quiet' PN-spectrum.
I then did some SPICE simulations [2] (never trust them without testing ;)
which indicated ADA4899 would be a good op-amp. In practice the
slew-rate/distortion was limiting and the AD4899 version didn't show better
PN.

This new version is inspired by looking inside a 6502[3] - and in the
mean-time I also measured and Ettus Octoclock [4] - but its performance
isn't so exciting..

My current design is now here: https://goo.gl/photos/WB8fYd4jzba7nXH18
So far my observations are:
- phase noise around -162 dBc/Hz at 10 MHz
- nice quiet PN-spectrum when unshielded and powered from lab-supplies
- this probably means the supply-section with common-mode choke, BNX025
filter and LT1963/LT3015 is working OK. I should probably build a
10Hz-100kHz LNA (e.g. [5]) to verify. I've used 2k@100MHz ferrites a lot
and an RC-filter on all supply pins - maybe overkill?
- an undesired feature is gain-peaking which increases from output ch1 to
ch8, shown here: https://goo.gl/photos/6QkoKakSPDdT7Acj7
I tried to improve it a bit by adding a 100pF cap at the start of the long
trace that feeds the output stages, but some gain-peaking still remains:
https://goo.gl/photos/qrkLzZ21ptcHxFsw6
- reverse isolation around 120 dB
- channel-to-channel isolation around 80 dB
- at 10MHz 1dB compression between +14 and +15 dBm
- IP3 perhaps +27dBm to +30 dBm.

Any ideas on how to deal with the long 'feeder-trace' that seems to be the
cause of the gain-peaking?
Anyway if not used at 100MHz perhaps my next version will have reduced BW
where the feeder-trace is not an issue..
Another issue is that the voltage regulators get quite hot when fed at
+/-12V and producing +/-6V. They should probably be positioned as far away
from the input/output amps and thermally disconnected if possible. I have a
+/-12V AC/DC brick on order - but a DIY linear PSU producing e.g. +/-8VDC
for the regulators might be better.

The picture gallery also shows a pulse distribution amp for 1PPS. It has an
LT1711 comparator feeding an 74AC14 buffer with length-matched traces to
74AC04's at the outputs. So far my length-matching didn't give zero
output-skew between the outputs - I see around 150-200ps skew which I tried
to tune a bit with wires and 0R resistors - without very much success.. any
ideas for improving this - or just leave it at 200ps skew?

cheers,
Anders

[1]
http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-first-tests/
[2]
http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-v2-simulations/
[3]
http://www.anderswallin.net/2016/02/symmetricom-6502-distribution-amplifier/
[4]
http://www.anderswallin.net/2016/09/ettus-octoclock-distribution-amplifier/
[5] http://cds.linear.com/docs/en/application-note/an83f.pdf
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