[time-nuts] Yet another GPSDO - locking to 10MHz
rbenward at verizon.net
Mon Jun 28 00:59:51 UTC 2010
All this talk about interpolation reminds me of a little neat chip by Analog
Devices, AD9500. It's programmable digital delay, bit, with lops resolution
with a loons full-scale range. I believe (from app notes) you can push it
to 100us FS, giving 390ns resolution. I think the minimum jitter at the
lowest FS was about lops. The AD9500 is cell and the 9501 is TTS.
----- Original Message -----
From: Murray Greenman
To: time-nuts at febo.com
Sent: Sunday, June 27, 2010 3:14 PM
Subject: [time-nuts] Yet another GPSDO - locking to 10MHz
I have a design which locks a high performance 10MHz OCXO to a 10MHz
source which should work equally well with the LEA5, or any source of 5
I designed it for use with a distributed factory GPS reference which has
picked up noise, hum and phase modulation, in order to deliver a high
quality but GPS locked reference direct to equipment. The design adds
nearly three orders of improvement.
Essentially it divides the incoming 10MHz by 16384 and compared the
phase with a similar division from the OCXO, within an ATTiny2313 micro.
The phase detector is a D-flip-flop type implemented in software (in
interrupts), and it delivers a locked reference with ADev around 10e-12
for Tau between 1s and 20s. The micro also keeps a real time clock and
does various background monitoring and telemetry tasks. There is PC
monitoring software as well. There are only four chips in the design.
While I can't share the code (belongs to my employer), the idea is
simple enough and I could share the schematic.
Eight of these units have been built. I used the excellent Rakon
Murray Greenman ZL1BPU
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