[time-nuts] ACAM GP22 Chip

Thomas Allgeier th.allgeier at gmail.com
Thu Nov 26 05:23:54 EST 2015

Hello Angus,

That is roughly what I want to do, a plausibility check if what I see is 
caused more by the GP22 or already present on the signal I am trying to 
Very clearly there is no principal problem, the data I get from the GP22 is 
pretty decent and with enough filtering already useable. I have the feeling 
the GP22 does not add very much noise/jitter and all I want is get a handle 
on how much in reality.

If we take this approach further we will have to invest in some additional 
kit, but apart from that I am also rather taken by the capabilities of the 
GP22 as a timer, and my own curiosity wants to find out how good a homebrew 
counter/timer could be built from it.

As I said I will feed back anything I can establish in this respect.

Best regards,

-----Original Message----- 
From: Angus
Sent: Thursday, November 26, 2015 1:54 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] ACAM GP22 Chip

>I wouldn't expect the noise to
>be in the ns range, but i wouldn't surprised if it was a few 10ps.
>I have never done any measurements though, and I don't think i've
>ever seen any jitter measurements for 32kHz oscillators, so take
>this value as rough guestimate.

On the GP21 board I used it was more like 10ns+. I don't know if
that's typical, but it wasn't a even particularly cheapo crystal as
the original one was faulty and I had to replace it. The official acam
board might be better, but the data sheet specifically talks about the
32K osc having a lot of jitter.

One of the problems of the data sheet is that it is really tailored
for those using it as a flow converter - some of the text does not
even make sense otherwise. That was one of the reasons I was planning
to test it more as a TDC, but just getting back to doing that now.

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