Circuit for extracting periodic signals from high noise backgrounds - uses randomly switched capacitors with outputs fed via high impedance separator and summers to operational amplifier

摘要

The circuit is for extracting a periodic signal from a high noise level background, normally from a photo or chemo-electric sensor. The circuit is based on the use of separation capacitors, a low pass filter and amplifier d.c. connected to a chopper circuit controlled by logic signals in phase with the incoming signal. The capacitors are charged during each useable part of the signal, their voltages being read out to a very high impedance separator. The closure of each capacitor circuit is completely random, the synchronising frequency determining the closed period of each part of the overall capacitor circuit. Chopping of the light output is by a three slot rotating disc between the source and the sensor. The base of each source has the same diameter as the sensor.