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Sensitivity improvement of a photoresistive image sensor with novel programmable dual element readout and calibration method

This paper describes a novel readout integrated circuit (ROIC) for a nanoscale photoresistive image sensor array with a novel dual element readout and calibration method. The dual element readout increases detector signal sensitivity and sensor dynamic range. It works on the assumption that adjacent nanoscale detectors have similar illumination levels. A novel on-chip two-point calibration method is also proposed; two on-chip 12-bit R-2R ladder digital-to-analog converters (DAC) are used for offset calibration, whereas the variable-gain switched-capacitor amplifier enables the gain calibration. The programmability feature allows the system to be converted to single element readout. Detector bias voltage is supplied by the two on-chip DACs and is programmable between 0 to 1.8 V for ROIC performance optimization. This image sensor and ROIC system is intended to be used as an endoscope camera which demands strict silicon area and low power consumption requirements. A sample 1×16 line sensor is used for proof of concept. This work focuses on the analog signal processing chain of the ROIC. The column-wise design makes the ROIC scalable for larger image sensor sizes. The proposed ROIC is designed in 0.18 μm CMOS process and the system is verified with post-layout simulations.