[time-nuts] Fast risetime pulse generator

Gerhard Hoffmann dk4xp at arcor.de
Wed Apr 13 04:16:39 EDT 2016


Am 13.04.2016 um 07:03 schrieb Bill Byrom:
> I agree with earlier comments that the Analog Devices SiGe voltage
> comparators appear to be a good choice, with 37 ps typical rise/fall
> (20%/80%):
> http://www.analog.com/media/en/technical-documentation/data-sheets/ADCMP580_581_582.pdf
> The evaluation board single unit price is about $299:
> http://www.analog.com/media/en/technical-documentation/evaluation-documentation/310187823ADCMP572_3_80_1_2EB_0.pdf
>   
>
If that is too much, you can do it in the style of my home-etched quickie:
18 * 14 mm, 0.5mm thick FR4. The trick is to get from chip output into
the semi-rigid coax as quickly as possible. The CML outputs have an
integrated 50 Ohms back termination. SMA launchers will probably
complicate things.

This is what has generated the waveforms in my previous post. Note that
the 20 GHz sampler is already close to its own risetime limit, so what
you see is probably worse than reality. I should have used the 50 GHz
plug in with its 9 ps risetime but then I usually avoid that because
I don't want to put it in jeopardy.

If one wants more voltage, an alternative might be a driver for 10 GBPS
DFB laser diodes. 5V in 35 ps seems possible.  ADN2525 or so.

Hittite is now AD. That is a good thing. Mouser or Digikey and no longer
prices and old data sheets under NDA.

If you think at Potato Semi chips, watch the loading conditions. Buffers
that can barely drive a 0.6 pF FET probe are a bad joke.

regards, Gerhard


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