A 9-μm Precision 5-MSa/s Pulsed-Coherent Lidar System With Subsampling Receiver

This letter presents a 19.5-GHz pulsed-coherent ranging system with an optical transmitter and an electrical subsampling receiver. A laser source is modulated by two electrical-optical modulators with two-level modulation at 19.5-GHz RF carrier frequency and 140-MHz pulsed modulation. At the receiving end, an analog front-end down-converts the echoed signal to 4.87-GHz IF, and an ADC directly subsamples the IF signal. The segmented time-of-flight information is then decoded by a digital signal processor. A proposed envelope detection reduces the nonlinearity which varies with signal-to-noise ratio (SNR) thus enhances the receiver's sensitivity. This envelope detection also eases the handoff between the coherent detection and the envelope detection. In a free-space measurement, this prototype achieves 9-μm precision, 5-MHz sampling rate, and 100-μm maximum INL across the 10-cm dynamic range at 2.5-m displacement.