Scan holding circuit for phase discriminator - has generating circuit separated from holding capacitor by three switches reducing interference to min.

摘要

The circuit generates a saw-tooth voltage with phase and period equal to those of a reference voltage. The sawtooth generator can be connected to a holding capacitor through two switches connected in series. They are made conducting or blocked depending on the phase difference between the reference voltage and a further voltage of the same frequency. The capacitor is followed by an amplifier with high input impedance, pref. a voltage follower. In order to reduce interferences from the reference voltage (S2) to the scanning holding circuit (3) output signal (Um) the two switches (K1, K2) are always switched together. A third switch (K3) is controlled, by a switching signal (S2) complementary to the switching signal (S2) so that the holding capacitor (CH) is to the highest degree screened from the a.c. voltage component passing through the blocked switch (K1). In order to shorten transient processes capacitance of the capacitor (CH) is small in comparison with that of capacitor (C1) generating the saw-tooth voltage.