Analog Front-end Readout Circuit For APD_Based LiDAR

Recently,with the rapid development of space surveying and intelligent driving vehicles,the application of LiDAR is increasingly extensive.Among them,the APD detector in linear mode has become the main detector for these LiDAR.Since the induced signal of linear-APD is a microampere current pulse of narrow pulse width,weak current detection and response to narrow pulse signal are the key points and difficulties in the design of LiDAR analog front-end readout circuit.In order to meet the need of miniaturization of lidar,a high integrated APD analog front-end readout circuit chip is designed and implemented in this paper.Based on the analysis of the principle of lidar and the characteristics of APD detector,we put forward an integrated high-gain broadband transimpedance amplifier(Transimpedance Amplifier,TIA),fixed gain voltage amplifier,high-speed real-time comparator and Low voltage differential signaling(LVDS)output interface dedicated chip architecture.The chip integrates discrete components in the conventional LiDAR ranging system,which is conducive to reducing the noise introduced by the interconnection of discrete components on the PCB and improving system reliability.The circuit was designed and implemented with 0.18?m CMOS process,the power supply voltage is 3.3V.The area of chip is about 0.9×1.9mm~2.After the test,the gain is 83.6 dB?,bandwidth is about120 MHz.The whole circuit can respond to the narrow pulse current signal with pulse width of 5ns and rising and falling time of 1ns,and the output signal meets the LVDS standard.The input noise current is about 23.5nA.The quiescent current is about 63mA,of which TIA current is about 30 mA.Based on the test results,the original TIA structure was improved in this paper,and the regulated cascode(RGC)TIA suitable for 32-line detector was designed,and the current rudder DAC was introduced to adjust current signal.The improved circuit was designed and simulated with 0.18?m CMOS process,the bandwidth can achieve129MHz with the gain of 15k?,and 780MHz with the gain of 2k?,static current reduced to 11.8 mA.