Analog signal pre-processing for performance enhancement of a distance meter based on frequency-modulated continuous-wave interferometry

A method for the processing of signal from an absolute distance meter based on a frequency-modulated continuous-wave (FMCW) interferometer is presented. FMCW is implemented using a laser diode driven by a current waveform obtained as the superposition of a triangular signal to a bias current kept well above the diode lasing threshold. The analog signal pre-processing includes a derivative block followed by the time-variant baseline restoration of the photodetector current. A high signal-to-noise ratio is ensured by avoiding the use of a resistive transimpedence preamplifier and subsequent voltage processing. The paper details the scheme of the pre-processing chain as well as the experimental results from an actual prototype of a distance meter.