Re: [casper] ROACH2 sync_out

[Zhu, Yan]

Hi Michael and all,

I'm also intended to use sync_out or other GPIO to output square wave to 
control noise source,

I measured 6V for sync_out and GPIO pin 1.5V.

After digging into ROACH2 schematics(page 25 in 
roach2_rev2_schematics.pdf),
I found the differential signal is first converted into single ended by 
SN65LVDT2 than

buffered out by THS3091. The THS3091 is given a 12V supply.
After a quick look at THS3091 datasheet, it will output about 12V at 
50Ohm load with 15V VS
and 3V with 5V VS, so 6~7V output is reasonable for 12V power supply(a 
little lower than expect?).


Can anyone remember why pull the sync_out that high instead of normal 
TTL or CMOS level?
If I want to use it to drive a load which expect TTL or CMOS level, how 
should I connect them?



Thanks
Yan





-- Original Message --
From: "Michael D'Cruze" 
To: "casper@lists.berkeley.edu" 
Sent: 2017-05-12 02:10:26
Subject: [casper] ROACH2 sync_out


Dear all,



I’m planning to use a 0.5Hz square wave, generated from the FPGA and 
output via sync_out, to eventually fire our cal diode (via much 
cabling). A quick hardware test today shows the sync_out port driving 
at circa 7V (!). This is a bit higher than I was expecting. Does this 
venture as a whole seem like a particularly bad idea to anyone with 
experience using sync_out? Is this output voltage roughly as expected?




Thanks a lot,

Michael



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Re: [casper] ROACH2 sync_out

[Dan Werthimer]

hi zhu yan and michael,

to bring the roach2 sync output voltage down to 0 to 5 volts when driving
50 ohms,
you could use a connectorized 50 ohm 3 dB attenuator.

a 3 dB attenuator should lower the voltage from 0 to 7 volts, down to 0 to
5 volts.

best wishes,

dan



On Thu, May 18, 2017 at 1:31 AM, Zhu, Yan  wrote:

> Hi Michael and all,
>
> I'm also intended to use sync_out or other GPIO to output square wave to
> control noise source,
> I measured 6V for sync_out and GPIO pin 1.5V.
>
> After digging into ROACH2 schematics(page 25 in
> roach2_rev2_schematics.pdf),
> I found the differential signal is first converted into single ended by 
> SN65LVDT2
> than
> buffered out by THS3091. The THS3091 is given a 12V supply.
> After a quick look at THS3091 datasheet, it will output about 12V at
> 50Ohm load with 15V VS
> and 3V with 5V VS, so 6~7V output is reasonable for 12V power supply(a
> little lower than expect?).
>
> Can anyone remember why pull the sync_out that high instead of normal TTL
> or CMOS level?
> If I want to use it to drive a load which expect TTL or CMOS level, how
> should I connect them?
>
>
> Thanks
> Yan
>
>
>
>
>
> -- Original Message --
> From: "Michael D'Cruze" 
> To: "casper@lists.berkeley.edu" 
> Sent: 2017-05-12 02:10:26
> Subject: [casper] ROACH2 sync_out
>
> Dear all,
>
>
>
> I’m planning to use a 0.5Hz square wave, generated from the FPGA and
> output via sync_out, to eventually fire our cal diode (via much cabling). A
> quick hardware test today shows the sync_out port driving at circa 7V (!).
> This is a bit higher than I was expecting. Does this venture as a whole
> seem like a particularly bad idea to anyone with experience using sync_out?
> Is this output voltage roughly as expected?
>
>
>
> Thanks a lot,
>
> Michael
>
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Re: [casper] ROACH2 sync_out

[Matt Dexter]

Hi,

Won't the U70 output, when divided by 2 by R450 and R452, need
to match the output signal from U71?
That suggests something like 2*(3.0 to 3.3V) =
  6.0 to 6.6V at U70 pin 6.

I can readily guess the designer wanted at least a few
outputs from the Roach that would emmulate COTS 1PPS sources and
those often drive TTL or 5V CMOS levels when terminated
in 50ohms.

I would distribute a signal from a 50 ohm source such as at J11
using 50 ohm coax and terminate into a 50 ohm load.  This way
clean transmission with minimal unwanted reflections that could
cause multiple edges or other signal integrity features.
If the ultimate receiving circuit was high impedance, as in
a standard TTL or CMOS logic gate, I'd place inline at the
receiving end of the 50 ohm coax cable a 50ohm feed-through
terminator.


Matt



On Thu, 18 May 2017, Zhu, Yan wrote:


Date: Thu, 18 May 2017 08:31:33 +
From: "Zhu, Yan" 
To: Michael D'Cruze ,
"casper@lists.berkeley.edu" 
Subject: Re: [casper] ROACH2 sync_out

Hi Michael and all,

I'm also intended to use sync_out or other GPIO to output square wave to
control noise source,
I measured 6V for sync_out and GPIO pin 1.5V.

After digging into ROACH2 schematics(page 25 in
roach2_rev2_schematics.pdf),
I found the differential signal is first converted into single ended
by SN65LVDT2 than
buffered out by THS3091. The THS3091 is given a 12V supply.
After a quick look at THS3091 datasheet, it will output about 12V at
50Ohm load with 15V VS
and 3V with 5V VS, so 6~7V output is reasonable for 12V power supply(a
little lower than expect?).

Can anyone remember why pull the sync_out that high instead of normal TTL
or CMOS level?
If I want to use it to drive a load which expect TTL or CMOS level, how
should I connect them?


Thanks
Yan





-- Original Message --
From: "Michael D'Cruze" 
To: "casper@lists.berkeley.edu" 
Sent: 2017-05-12 02:10:26
Subject: [casper] ROACH2 sync_out

  Dear all,



  I’m planning to use a 0.5Hz square wave, generated from the
  FPGA and output via sync_out, to eventually fire our cal
  diode (via much cabling). A quick hardware test today shows
  the sync_out port driving at circa 7V (!). This is a bit
  higher than I was expecting. Does this venture as a whole
  seem like a particularly bad idea to anyone with experience
  using sync_out? Is this output voltage roughly as expected?



  Thanks a lot,

  Michael

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RE: [casper] ROACH2 sync_out

[Michael D'Cruze]

Hi all,

I should clarify that having the extra amplitude is actually beneficial to our 
application, rather than detrimental. I was concerned that the electronics 
might have been driving too hard, risking future failure, for example.

BW
Michael

From: dan.werthi...@gmail.com [mailto:dan.werthi...@gmail.com] On Behalf Of Dan 
Werthimer
Sent: 18 May 2017 15:36
To: Zhu, Yan
Cc: Michael D'Cruze; casper@lists.berkeley.edu
Subject: Re: [casper] ROACH2 sync_out



hi zhu yan and michael,

to bring the roach2 sync output voltage down to 0 to 5 volts when driving 50 
ohms,
you could use a connectorized 50 ohm 3 dB attenuator.

a 3 dB attenuator should lower the voltage from 0 to 7 volts, down to 0 to 5 
volts.

best wishes,

dan



On Thu, May 18, 2017 at 1:31 AM, Zhu, Yan 
mailto:zhu...@nao.cas.cn>> wrote:
Hi Michael and all,

I'm also intended to use sync_out or other GPIO to output square wave to 
control noise source,
I measured 6V for sync_out and GPIO pin 1.5V.

After digging into ROACH2 schematics(page 25 in roach2_rev2_schematics.pdf),
I found the differential signal is first converted into single ended by 
SN65LVDT2 than
buffered out by THS3091. The THS3091 is given a 12V supply.
After a quick look at THS3091 datasheet, it will output about 12V at 50Ohm load 
with 15V VS
and 3V with 5V VS, so 6~7V output is reasonable for 12V power supply(a little 
lower than expect?).

Can anyone remember why pull the sync_out that high instead of normal TTL or 
CMOS level?
If I want to use it to drive a load which expect TTL or CMOS level, how should 
I connect them?


Thanks
Yan





-- Original Message --
From: "Michael D'Cruze" 
mailto:michael.dcr...@postgrad.manchester.ac.uk>>
To: "casper@lists.berkeley.edu" 
mailto:casper@lists.berkeley.edu>>
Sent: 2017-05-12 02:10:26
Subject: [casper] ROACH2 sync_out

Dear all,

I’m planning to use a 0.5Hz square wave, generated from the FPGA and output via 
sync_out, to eventually fire our cal diode (via much cabling). A quick hardware 
test today shows the sync_out port driving at circa 7V (!). This is a bit 
higher than I was expecting. Does this venture as a whole seem like a 
particularly bad idea to anyone with experience using sync_out? Is this output 
voltage roughly as expected?

Thanks a lot,
Michael
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Re: [casper] ROACH2 sync_out

[Dan Werthimer]

i think matt is right about the sync output voltages and impedance.

the roach2 sync output should be about 0 to 6 volts with no load,
and about 0 to 3 volts when this signal is terminated in 50 ohms.

so no attenuator is needed if the sync signal is connected to a 50 ohm
load.
if the device that is receiving the sync signal doesn't have a 50 ohm input,
then matt's suggestion of adding an inline connectorized 50 ohm terminator,
or using a T and 50 ohm termination resistor will get the voltage to
CMOS/TTL levels.

best wishes,

dan


On Thu, May 18, 2017 at 1:31 AM, Zhu, Yan  wrote:

> Hi Michael and all,
>
> I'm also intended to use sync_out or other GPIO to output square wave to
> control noise source,
> I measured 6V for sync_out and GPIO pin 1.5V.
>
> After digging into ROACH2 schematics(page 25 in
> roach2_rev2_schematics.pdf),
> I found the differential signal is first converted into single ended by 
> SN65LVDT2
> than
> buffered out by THS3091. The THS3091 is given a 12V supply.
> After a quick look at THS3091 datasheet, it will output about 12V at
> 50Ohm load with 15V VS
> and 3V with 5V VS, so 6~7V output is reasonable for 12V power supply(a
> little lower than expect?).
>
> Can anyone remember why pull the sync_out that high instead of normal TTL
> or CMOS level?
> If I want to use it to drive a load which expect TTL or CMOS level, how
> should I connect them?
>
>
> Thanks
> Yan
>
>
>
>
>
> -- Original Message --
> From: "Michael D'Cruze" 
> To: "casper@lists.berkeley.edu" 
> Sent: 2017-05-12 02:10:26
> Subject: [casper] ROACH2 sync_out
>
> Dear all,
>
>
>
> I’m planning to use a 0.5Hz square wave, generated from the FPGA and
> output via sync_out, to eventually fire our cal diode (via much cabling). A
> quick hardware test today shows the sync_out port driving at circa 7V (!).
> This is a bit higher than I was expecting. Does this venture as a whole
> seem like a particularly bad idea to anyone with experience using sync_out?
> Is this output voltage roughly as expected?
>
>
>
> Thanks a lot,
>
> Michael
>
> --
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