A Compact Low-Noise Digital Pixel with 15-bit Two-Step PFM-based ADC for IRFPAs

A compact low-noise digital pixel with 15-bit pixel-level two-step analog-to-digital converter (ADC) is presented in this paper. The coarse quantization adopts a 10-bit pulse frequency modulation conversion with a proposed threephase charge-reset circuit. The charge-reset circuit reduces the reset noise charge which is the major noise of this pixel. The fine quantization is implemented by a 5-bit single-slope ADC. It reuses most of the coarse quantization circuit to realize high precision quantization in compact pixel. A 640×512 readout integrated circuit for infrared focal plane array with the 15μm pitch digital pixel is designed in the 0.18 μm1P5M CMOS process for verification. Post-layout simulation results of the digital pixel show that the RMS noise at maximum signal is 0.51LSB, and the integral nonlinearity is +2.3LSB/-3.0LSB. The power consumption per pixel is only 57. 2nW at 120fps.