[time-nuts] 5 MHZ PIC PPS Divider?
bruce.griffiths at xtra.co.nz
Tue Apr 15 20:02:22 EDT 2008
Bruce Griffiths wrote:
> Stanley Reynolds wrote:
>> Thanks Pete not sure my wife will let another big box in the door. I was thinking of some thing like this :
>> a ECL 8-Bit Ripple Counter. And a 1Ghz oscillator make the measurement of differences. This should get me to the 1ns level ?
>> But looking at the sampling heads may be close to what I want, I will look for some manuals on the web. I would want to transfer the data to a PC, would I need a GPIB Interface and some software ? I'm trying to eliminate the extra stuff like the scope tube and it's power supply and end up with a small box to interface to the computer.
Yet another technique is to low pass filter the PPS signal and sample it
with a pipeline or similar high speed ADC clocked at say 100MHz (phase
locked to the 10MHz standard).
Then process the ADC output to determine the midpoint of the filtered
PPS transition with subnanosecond (100ps should be easy to achieve)
Only the conversions near the transition need be stored the others
merely need to be counted.
An FPGA makes this easy and since there is only one such transition per
second a relatively slow processor should suffice.
With the right FPGA you can "build" the processor right into the FPGA
The Xilinx Spartan II starter kit, for example allows this, all you need
do is connect it to the ADC board and use the built in LAN or serial
port connection to connect to a PC.
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