Alpha’s series of Sampling Phase Detectors (SPD’s)
consist of a hybrid assembly of an SRD comb
generator, coupling capacitors and microwave mixer
diodes. This module makes an inexpensive way of
phase locking a commercial VCO source to a low
frequency stable reference. Each part in the series is
optimized to operate in standard narrow band
commercial systems. All units handle reference
frequencies in the 50 to 500 MHz band. Component
selection within Alpha allows us to minimize beat note
output.
It is easiest to think of the SPD in its two constituent
forms; a comb generator and subharmonic mixer.
The comb generator portion consists of the external
reference, amplifier and impedance transformer. The
external circuit matches into the low impedance of the
SRD portion of the SPD. Careful attention to matching
by setting the right transformer ratio, detuning the circuit with shunt capacitors will result in larger
amplitude beat note signals.
The subharmonic mixer portion is the Schottky series
pair. Various drive levels can be used to tailor
intermodulation and beat note performance
The basic operation of a SPD is when the reference
signal is fed into the SRD. This sets up a strong pulse,
rich in harmonics that is used to strobe the mixer
diodes on. The balanced mixer design converts the
sampled oscillator signal and matching harmonics into
an IF beat note. This signal can then be used in
feedback loop to correct tuning voltage on the VCO
Typical applications include phase locking of
oscillators in TVRO, VSAT, DBS and
telecommunications markets.
Photos under microscope upon request
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