JPS6472092A - Distance measuring instrument - Google Patents

Abstract

PURPOSE:To accurately perform distance measurement by correcting a detected phase difference by a quantity of phase shift detected at an AGC circuit. CONSTITUTION:The quantity of phase shift in a variable gain amplifier circuit 6 is measured setting a gate voltage from an A/D conversion circuit 12 as a parameter, and it is stored in a phase shift correction table 13. The output signal of a photodetector 2 is supplied to the circuit 6, and feedback control applied so as to always keep the amplitude of the output signal of the circuit 6 constant by an amplitude detection circuit 11, and also, the quantity of phase shift is detected based on the control signal of the gain of the AGC circuit 4. The reference signal of an oscillation circuit 3 and the output signal of the circuit 4 are supplied to a phase difference detection circuit 5, and the apparent phase difference of both signals is detected, and it is supplied to the (+) termi nal of a differential circuit 15 via an A/D conversion circuit 14. By supplying a gate voltage from the circuit 11 to the table 13, a corresponding quantity of phase shift is read out from the table 13, and is supplied to the (-)terminal of the circuit 15, and the apparent phase difference detected at the circuit 5 is corrected, thereby, a correct phase difference can be obtained. By using such phase difference, a distance can be measured accurately.