ERROR ANALYSIS OF PHASE-SHIFT LASER RANGEFINDER WITH HIGH-LEVEL SIGNAL

The amplitude of the photoelectric current delivered by the photodiode of a I-IO m phase-shift laser rangefinder varies by a factor greater than 1000. With high levels,amplitude distortion generates a phase-shi ft error in mixing circuits. A model is proposed to analyse this error . It demonstrates that such an error can be suppressed with a clipper differential circuit, the load impedances of which are compensated, an d by generating the harmonics of a useful signal on the local oscillat or with a differentiated square wave. Theoretically, an improvement of more than 30 times may be achieved with a phase-shift error less than 0.1 degree for a 20 MHz frequency. Experimentation at 10 MHz shows th at the new circuit is implementable and strongly reduces the error int roduced by the usual one. (C) 1997 Elsevier Science S.A.