Electronic evaluation circuit for ultrasonic movement detector - uses Doppler-Fizeam effect and has high gain transistor amplifiers

摘要

The detector uses an ultrasonic transceiver (3) coupled to a high gain voltage amplifier (4) for amplifying the fundamental frequency and the LF modulation frequency. Its output is coupled via a voltage divider (5) to a second high gain amplifier (6) followed by voltage doubler demodulator (8,9) and an RC filter (10,11) for eliminating the HF carrier. The resulting signal is supplied via a further high gain amplifier (12) and further voltage doubler demodulator (13,14) to a LF amplifier (15) which is followed by a second RC filter. The LF amplifier output controls a multivibrator (21,22) providing a control pulse. Pref. transistors in common-emitter configuration are used as the high gain amplifiers (4,6,12) and diode pairs are used as the voltage doubler demodulators (8,9;13,14).