Near-Infrared Array Receiver for Real-Time 3D Imaging Application

In this paper, a near-infrared array receiver consisting of two 16-element linear-arrays InGaAs reach-through avalanche photodiodes and readout circuit assembled by system-level integrated package was developed for 3D realtime imaging. The readout circuit includes 32 transimpedance amplifiers, double-threshold comparators and time-to-digital converters (TDC). With transimpedance amplifier based on closed-loop structure of inverter-like amplifier circuit, and post-stage differential output amplifier, the readout circuit can achieve high gain, large bandwidth and low noise. The double threshold comparator was used to solve walking error. With two-step architecture combining 8-bit coarse counting and 6-bit fine counting, the dynamic range of the receiver is increased by coarse counting while its resolution is improved by combining fine counting. When the system emits a laser pulse, the receiver starts timing and converts the echo signal to a voltage signal. When a stop timing signal is generated, the system quantifies the time of flight to 14-bit digital signal. The developed receiver demonstrates the pulse responsivity of $\mathbf{5.4}\times 10^{5}\ \mathbf{V}/\mathbf{W}$, the 3dB bandwidth of 142.9 MHz, the minimum detectable optical power of about 26.7 nW $(\mathbf{SNR}=10)$, and the time resolution of 200 ps. When the receiver is applied to a lidar system, where a 1550 nm semiconductor laser illuminates the target scene with pulse width shorter than 10 ns and repetition frequency more than 20 kHz, combining timing control with software algorithm, we get a clear environmental 3D image in real time.