Pixel-Level Sequential TDC With Wide Dynamic Range for Large-Array Microbolometer IRFPAs

Abstract

A digital readout integrated circuit (DROIC) incorporating a pixel-level sequential time-to-digital converter (TDC) is studied for microbolometer infrared focal plane arrays (IRFPAs). To improve signal-to-noise ratios (SNRs) with sufficient integration time for IRFPAs with large arrays and small pixel sizes, a sequential driving method with high precision bias suppression is used. A pixel-level TDC with a single-slope analog-to-digital converter (SS-ADC) is proposed to improve dynamic range (DR) and SNR over a wide input range despite low supply voltage and power consumption. The readout circuit is fabricated using a 0.18 mu m standard CMOS process for 1026 x 768 arrays with a pixel size of 15 x 15 mu m. The maximum integration time and DR are 1.95 ms and 80.9 dB, respectively, with a power consumption of 0.21 mu W per pixel.