Design of a CMOS ROIC for InGaAs Self-Mixing Detectors Used in FM/cw LADAR

A scannerless laser detection and ranging (LADAR) system based on frequency modulation/continuous wave (FM/cw) technique is attractive due to a reduced bandwidth requirement of the receiver circuit. This paper presents the 64x64 InGaAs-based focal plane array (FPA) self-mixing detectors and the 1x32 element readout integrated circuit (ROIC) array based on transimpedance amplifier for the FM/cw LADAR. Different from conventional detector, the InGaAs self-mixing detector presents a low impedance and a complex electrical model. The linear chirp local-oscillator (LO) electrical signal through the detector causes a large dc current and a unique dc offset voltage (Vos) error in the ROIC. To overcome these problems, the blocking capacitors and the novel multiple low-pass filters are applied in the ROIC. The ROIC array was fabricated in 0.18-mu m CMOS process. The measured results show that the Vos error is eliminated within the limited LO amplitude range and the ROIC achieves a 140-dB Omega transimpedance gain with a bandwidth of 1 MHz. Compared with the state-of-the-art FM/cw LADAR, the ROIC accurately detects the signal of interest of the InGaAs FPA self-mixing detectors and miniaturizes the LADAR receiver.