Harmonic Determination Circuitry; Sampling Theory; Sampling Diode Switch; Balanced Sampler - HP 5340A Operating And Service Manual

4-124. Harmonic Determination Circuitry

4-125. When sampler No. 2 produces a n F I F ~ output, the bandpass filter and preamp A2A4
provide a 6 MHz bandpass.
reference from A15. When 20 MHz is mixed with
to N 20 kHz is produced. The value of N is determined in the counter circuits and used as a gate
extension factor.

4-126. SAMPLING THEORY

4-127. Sampling techniques are used for measuring frequencies that are too high to count with
direct counting circuits. This method provides a n output signal whose frequency is a fraction of
the input frequency and low enough to count directly. The 534QA uses a 20 MHz phase lock loop.
However for simplicity, a dc phase lock loop will be described followed by a n explanation of the
type of phase lock techniques used in the 5340A.
4-128. A sampler looks at the input signal for a brief interval of time and charges a capacitor
to the instantaneous voltage of the signal. For each sample event, the capacitor charges to the
instantaneous voltage of the input waveform. Figure 4-46 shows one method of sampling using a
diode as a switch.
INPUT
SIGNAL
4-129. To minimize sampling pulses on the input signal, a balanced sampler is used a s shown in
Figure 4-47. The outputs of the balanced sampler connect to a n amplifier for summing.
INPUT
Limiter amplifier-mixer A14 receives FIF2, and the 20 MHz
Figure 4-46. Sampling Diode Switch
Figure 4-47. Balanced Sampler
OUTPUT
TO
AMPL
Theory of Operation
difference frequency that is equal
OUTPUT TRANSMISSION
LINE
40 pS
Model 5340A
4-35