Design of an FMCW-LiDAR receiver front-end

Abstract

This work presents an analog front-end (AFE) signal processing chain for automotive FMCW LiDAR. The AFE consists of a high-gain transimpedance amplifier (TIA) followed by a gain-stage. The gain of the AFE is 103.2dBΩ at a bandwidth of 505MHz. Since the noise of FMCW-LiDAR systems is dominated by the shot noise of the local oscillator (LO), the AFE is noise matched to the optical system. It has an input-referred noise of 13pA/√Hz which is lower than the 16pA/√Hz generated by the optical system. The signal chain is designed to amplify the small single-ended photo current and convert it into a differential output voltage between 7mVpk and 125mVpk that is adequate for digitisation by an ADC. An SFDR=46.4dB is maintained to mitigate the generation of spurious tones, which will cause false object detections. The AFE circuits are sufficiently linear to ensure that such tones are below the noise floor. The signal path is AC-coupled to ensure that the balanced photodetector does not compromise the bias currents of the input stage. An external coupling capacitor defines a 1MHz high pass corner. The AFE was implemented in 0.13μm CMOS technology and occupies 1160μm x 585μm including all supporting circuitry. With a 1.5V power supply, the total power dissipation is 250mW including the ADC-driver. The project was finalised by integrating the AFE with an ADC and the required support circuitry into a full ASIC for use as a building block in LiDAR systems.