雪崩光电二极管(APD)具有频响宽、灵敏度高的优点, 在激光测距中有重要应用。为了分析APD电外差混频技术对系统信噪比的影响, 建立了APD的数学模型, 仿真分析了偏置电压直流分量与信噪比的关系, 以及APD击穿电压变化时对信噪比的影响。结果表明, APD电外差混频技术会降低APD输出信号的信噪比, 但它降低了后续电路处理带宽, 有利于系统整体信噪比的提升;当APD输入光信号较微弱时, 采用电外差混频技术, 可有效提高系统整体的信噪比。

Avalanche photodiode (APD) have been widely applied in laser ranging systems for high sensitivity and broad bandwidth. Based on the avalanche effect of an APD, adding a local oscillator signal to the APD bias voltage, optoelectronic heterodyne mixing is to make down converter of signal into realization. In order to analyze the effect of APD optoelectronic heterodyne mixing on signal-to-noise ratio (SNR) of a system, the mathematical model of an APD was built. The relationship between direct-current component of the bias voltage and SNR and the effect of APD breakdown voltage change on SNR were analyzed by simulation. The results show that SNR of the APD output signal is reduced by optoelectronic heterodyne mixing, however, the bandwidth of subsequent circuit is reduced too, which can improve SNR of the whole system. When the input signal of an APD is weak, optoelectronic heterodyne mixing of the APD can improve the SNR of the system.