The Sampling Phase Detector (SPD) module is a
hybrid circuit providing a fast Step Recovery Diode,
coupling capacitors and a low barrier Schottky pair.
The Schottky pair is used as a sampling circuit turned
on by the fast step from the Step Recovery Diode,
or in the frequency domain, the Schottkys act as a
mixer to mix the harmonic of the SRD step closest
to the microwave frequency. The output is a beat
frequency (the difference between the harmonic of
the reference and the microwave frequency) and is
just a DC voltage at the lock point. It is used to phase
lock DRO’s and VCO’s from 10 to 1000 MHz (TYP)reference frequencies.