A 2.7-M Pixels 64-mW CMOS Image Sensor With Multicolumn-Parallel Noise-Shaping SAR ADCs

Abstract

This paper presents a CMOS image sensor (CIS) utilizing a noise-shaping successive-approximation register analog-to-digital converter (SAR ADC) incorporating the delta-readout scheme. While the noise-shaping SAR ADC with a proposed two-tap passive finite-impulse response (FIR) filter improves effective resolution, the delta-readout scheme reduces its power consumption. A prototype <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1920\times 1440$ </tex-math></inline-formula> pixel CIS was fabricated in a 90-nm CIS process. A single-channel readout SAR ADC occupying an area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${22.4}\,\,\mu \textsf {m}\times {715}\,\,\mu \text{m}$ </tex-math></inline-formula> was implemented for reading out 16 columns of pixel array, consuming <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$437~\mu \text{W}$ </tex-math></inline-formula> . Owing to the proposed noise-shaping SAR ADC with oversampling ratio of 16, this paper achieves a noise reduction of 14 dB compared with the noise of a conventional SAR ADC. The delta-readout reduces the power consumption of the SAR ADC by 10% due to the high hit rate of the full high definition image format. The measured differential nonlinearity of the ADC is +0.77/ −0.54 LSB and the integral nonlinearity is +0.81/ −0.5 LSB. The prototype CIS consumes a total power of 64 mW and achieves a dynamic range of 66.5 dB and a figure of merit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$127~\mu \text{V}\cdot $ </tex-math></inline-formula> nJ at a data rate of 138 Mpixels/s.