5kHz ref from Copernicus II module

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rt54321
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Joined: Thu Sep 03, 2015 7:28 pm

5kHz ref from Copernicus II module

Post by rt54321 » Thu Sep 03, 2015 7:58 pm

Greetings all!

Somewhat of a phase-locked-loop and GPS question here. Using the Copernicus II module (for the PPS signal) and an MSP430 Launchpad, the application is to generate a 5kHz square wave that is phase-aligned to the GPS PPS signal. I know that there are modules out there that already do this, but I'm trying to DIY it (for cost, and for learning purposes).

In addition to the Copernicus II module and the MSP430, have the following:
10MHz VCO with small (+/- 5ppm) pull-in range
12 bit DAC (to interface the MSP430 with the VCO)
Bunch of 74LS90 chips to divide the 10MHz frequency down to 5kHz

What I've done so far: Once the Copernicus II module starts generating reliable PPS signals, I CAN get the VCO locked via the MSP430 (the MSP430 counts the number of VCO pulses between PPS signals, and if there are not 10,000,000, then adjust VCO as needed).
I can also get a 5kHz signal, by dividing down the above 10MHz VCO output.

What I can't figure out:
The 5kHz signal should also be phase-aligned to the PPS signal (that is, the first rising edge of the 5kHz signal, in one period, should be aligned with the rising edge of the PPS pulse). I am NOT certain how to do this.

It seems that I have made a frequency-locked loop, but not a phase-locked loop. Any suggestions, as to how I can do this?

Thanks for your help!
-R

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