Research On ROIC Design Technique For FM/cw LADAR Based On InGaAs FPA Detectors

Without the need of a wideband and high speed receiver,the imaging LADAR(Laser detection and ranging)based on frequency modulation/continuous wave(FM/cw)detection and ranging principle has obvious advantages on the high integration,miniaturization and low power consumption of LADAR system.As an important part of LADAR system,readout integrated circuits(ROIC)directly affects the detector performance.The detector used in FM/cw LADAR is an optoelectronic mixer,whose operating principle and parasitic effect are different from the conventional detectors.It puts forward new requirements and challenges for the ROIC.The design of the CMOS ROIC based on the InGaAs 64×64 focal plane array(FPA)self-mixing detectors is studied in this paper.The main contents are as follow:1.Based on the operating principle and the structural feature of the self-mixing detector,the effects of major external factors on the detector performance are investigated.Based on the tunnel effect of schottky barrier diode and photoelectric effect,the mixing mechanism of the detector is further expounded in theory.According to the developed equivalent circuit model of the detector,the main parasitic parameters are extracted for the ROIC design.2.Two kinds of RF(Radio frequency)multiplexer circuits were used to gating the RF local oscillator signal.They were fabricated in 0.35 ?m CMOS process and 0.18?m RF CMOS process,respectively.When the load is the FPA detectors,the simulated and measured results show that the former has an output voltage swing of 5 Vpp and a bandwidth of about 100 MHz,the latter has a bandwidth of about 300 MHz and an output voltage swing of 2.6 Vpp,and both the former and the latter have an isolation of better than 40 dB in the above bandwidths.3.The parasitic effect of the detector causes an output offset voltage drift of analog amplifier circuit.The cause is attributed to the nonlinear distortion of CMOS amplifier resulted by a parasitic large-signal.For solving this problem,an improved analog amplifier circuit is proposed in this paper.The circuit parameters are optimized and a multi-filtered procession is applied in the circuit.The measured results show the offset voltage drift is significantly reduced and the signal of interest of the detector is accurately detected.4.Due to the parasitic substrate coupling and through-space coupling,the analog amplifier circuit including a transimpedance amplifier and one or more voltage amplifiers is not stabilized at a high gain.In order to evaluate the stability,a new simulation model is proposed,which can reflect the effect of the parasitics on the stability.A compensation capacitor is utilized to improve the stability,and can have little effect on the bandwidth and gain.Experimental tests validated the proposed simulation model and compensation method.5.The 1×32 analog amplifier circuit array was fabricated in 0.18 ?m CMOS,and packaged with the FPA detectors.The measured results show the-3dB bandwidth of the analog amplifier circuit is from about 60 kHz to 1.1 MHz at a gain of about 140 dB?,and the maximum gain is 160 dB?@300 kHz.The FM/cw LADAR system employing the ROIC obtains the 4D imaging of the target.