Phase-shift errors of a balanced mixer with high level signal

The amplitude of photoelectric intensity current delivered by the photodiode of a laser rangefinder varies with a factor greater than 1000 versus distance and reflectance of the target. With high levels, amplitude distortion generates a phase-shift error in a double balanced mixer. The proposed modelling explains this error. It can be suppressed with a clipper differential circuit and by generating harmonics on the local oscillator channel with a differentiated square wave. The error of the differential input circuit is proportional to the product of input signal amplitude and frequency; a macro-model is suggested, in which errors from nonlinear operation are distinguished from errors from low level photoelectric signal