[time-nuts] Analog Phase comparator
bruce.griffiths at xtra.co.nz
Sun Sep 21 17:47:27 EDT 2008
The AD9901KP is available in a side brazed DIP package (at least its
listed as a current production device).
However Digikey for example, only stock the PLCC version.
With 10MHz inputs it should resolve a few tens of picosec of phase
With a 10 bit ADC the resolution would be about 200ps.
If you need more resolution use a higher resolution ADC.
If you need less resolution either use a lower resolution ADC or use
prescalers to reduce the AD9901input frequency.
To compensate for drift in the AD9901 gain one can
1) Use an ADC with its reference proportional to the AD9901 output stage
2) Servo the AD9901 output stage collector current to the ADC reference
3) Measure the AD9901 output stage collector current periodically and
use the measurement to correct phase detector output measurements for
Thus an AD9901 can be used to meet both low end and higher resolution
Biased in ECL mode it has input differential amplifiers suitable for
signals down to around a couple of hundred mV pp.
Since the AD9901 has a triangular phase detection characteristic a pair
of them with one input signal inverted for the the second are required
to determine the sign of the phase difference.
This is readily accomplished by swapping over the connections to one of
the differential input buffers of the second AD9901.
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