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

2017-09-22 Thread Anders Wallin 
On Sat, Jan 28, 2017 at 5:53 PM, Mattia Rizzi 
wrote:

> 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.
>

Hi Mattia, everyone,

I now had time to assemble a few distribution amplifiers using IDT5PB1108
(see [1], left side).
With my skills in length matching the traces (using Kicad) I still get
around 200ps peak-to-peak output skew between channels.
The chip datasheet spec is <50 ps pin-to-pin skew.

So now I tried adding a trimmer-cap on the input of the output-buffer.
I tried both 50pF and 10pF, but it seems 10pF gives a 500ps delay-tuning
range which is sufficient.
When tuning all channels to within 20ps P-P one day, I then got 50 ps P-P
when verifying this the next day.
Using BNC-cables and an SMA-BNC adapter on the output might not be the
greatest choice for picosecond repeatability...

I did the measurements with a 53230A and the reported values are the
average of 30-60 s of 1PPS pulses.
Some images with the board and results here:
http://www.anderswallin.net/2017/09/delay-tuning-with-trimmer-caps/

I also opened up a commercial pulse-distributor, and it has the same kind
of trimmer-caps before the output-stages.
It measured 28 ps peak-to-peak among 16 output channels.

I will incorporate a trimmer-cap into the next version of the "PDA" design
and publish on ohwr - when I have time..

Anders
[1] https://www.ohwr.org/attachments/5339
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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

2017-02-03 Thread Mattia Rizzi 
Hello David,

>200ps of skew is consistent with long traces on board material like
standard FR4 because of uneven dielectric constant

Can you elaborate it? What do you mean by "long traces"?
I saw the PCB done by Anders, the track length is about 10 cm. Using the
microstrip formula, even for a big dielectric change (Dk from 4 to 4.6,
worst scenario), the propagation speed change is about 5% (30ps).
Indeed, you'll get also reflections, but the effect is dwarfed by the "s"
done by Anders for length matching.
My gut-feeling is that most of the 200ps skew (80-85%) is coming from
74AC04's unmatched outputs, but since two persons already replied
suggesting PCB issues, I'm very interested.

cheers,
Mattia


2017-01-29 8:11 GMT+01:00 David :

> On Sat, 28 Jan 2017 13:58:27 +0200, you wrote:
>
> >...
> >
> >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
>
> 200ps of skew is consistent with long traces on board material like
> standard FR4 because of uneven dielectric constant produced by uneven
> fiberglass weave.  One way to ameliorate this is to route traces at a
> diagonal compared to the fiberglass weave.
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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

2017-01-29 Thread Charles Steinmetz 

Ruslan wrote:


Have you looked at the design of the HP/Agilent/Keysight E1750A (sine
timebase of various standard frequencies)...?


According to the specifications on the 5087A/E1750A/E1752A spec sheet, 
the 1750A is no better WRT phase noise than the 5087A, and the 5087A is 
distinctly ... mediocre ... in that regard (not helped at all by having 
an AGC loop).  Phase noise was obviously not HP's first design priority.


Since the OP is seeking better PN performance than his first design, 
which already has 10dB less PN than the 5087A, studying these HP 
distribution amp circuits will probably not be very instructive.


That said, if you have service manuals for the 1750A or 1752A, I'm sure 
many owners would be grateful if you post them -- they seem to be hard 
to find.  Didier's site is one good place:




Best regards,

Charles


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

2017-01-29 Thread Ruslan Nabioullin 

On 01/28/2017 06:58 AM, Anders Wallin wrote:

Hi all,
I've been tinkering with another distribution amplifier design and made
some measurements earlier this week.


Have you looked at the design of the HP/Agilent/Keysight E1750A (sine 
timebase of various standard frequencies) and E1752A (PPS) VXI plugins? 
They were designed and engineered in the 90s and were obsoleted by at 
least Keysight, but I recently purchased them due to their low cost and 
size savings (my lab is already filled with stacks of equipment).  Their 
theory of operation is described in the manual available on Keysight's 
website.


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

2017-01-29 Thread David 
On Sat, 28 Jan 2017 13:58:27 +0200, you wrote:

>...
>
>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

200ps of skew is consistent with long traces on board material like
standard FR4 because of uneven dielectric constant produced by uneven
fiberglass weave.  One way to ameliorate this is to route traces at a
diagonal compared to the fiberglass weave.
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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

2017-01-28 Thread 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 amplifier (again!) - now mostly ok but has gain peaking

2017-01-28 Thread 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

2017-01-28 Thread 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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Re: [time-nuts] Distribution amplifier (again!) - now mostly ok but has gain peaking

2017-01-28 Thread 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

2017-01-28 Thread 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

2017-01-28 Thread 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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