Fully differential CTIA cds for a 32x16 ROIC for 3D ladar imaging systems

This document describes a 2-D fully differential Readout Integrated Circuit (ROIC) designed to convert the photocurrents from an array of differential metal-semiconductor-metal (MSM) detectors into voltage signals suitable for digitization and post processing. The 2-D MSM array and CMOS ROIC are designed to function as a front-end module for an amplitude modulated/continuous time AM/CW 3-D Ladar imager under development at the Army Research Laboratory.; One important aspect of our novel ROIC design is scalability. Within reasonable power consumption and photodetector size constraints, the ROIC architecture presented here scales up linearly without compromising complexity. The other key feature of our ROIC design is the mitigation of local oscillator coupling. In our ladar imaging application, the signal demodulation process that takes place in the MSM detectors introduces parasitic radio frequency (rf) currents that can be 4 to 5 orders of magnitude greater than the signal of interest. We present a fully-differential photodetector architecture and a circuit level solution to reduce the parasitic effect.; As a proof of principle we have fabricated a 0.18 mum CMOS 32x16 fully differential ROIC with an array of 32 correlated double sampling (cds) capacitive transimpedance amplifiers (CTIA's), and a custom printed circuit board equipped to verify the test chip functionality. Test results show it to be a powerful architecture in terms of scalability and a solid option for highly-integrated active and passive imaging systems.