JPS56160669A - Synchronous detecting device - Google Patents

Abstract

PURPOSE:To improve an S/N ratio and to increase detecting sensitivity in the case of the detection and the like of minute variation in a differential transformer, by performing the synchronous detection by a full-wave detector. CONSTITUTION:Analog switches S1 and S2 are connectd to terminals (a) and (b) of a detecting coil 4. The analog switch S1 and S2 are reversely opened and closed based on a signal C which is synchronized with an exciting frequency (f) of a binary coding circuit 8 and a signal C' which is inverted in an inverting element 10. The terminals (a) and (b) repeat opening and grounding at every half cycle. In the case the phase of the exciting voltage Vf is the same as that of the detected signal, S1 is opened and S2 is closed at the first half cycle of the detected signal, and the output Vd of an operational amplifier 7 becomes Vd=-RoVa/R1. At the second half cycle, since Vd=RoVb/R2, and if R1=R2, the output voltage Vd of the operational amplifier can be obtained as a full-wave rectified waveform, which is the amplified result of the detected signal by Fo/R1 times. Thus the efficiency can be enhanced and the S/N ratio can be improved.