[time-nuts] Yet another GPSDO - locking to 10MHz

Robert Benward 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.


app note



  ----- 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
  or 10MHz.

  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
  STP2402E OCXO.

  Murray Greenman ZL1BPU

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