The Scientific World Journal (Jan 2014)

Two-Step Single Slope/SAR ADC with Error Correction for CMOS Image Sensor

  • Fang Tang,
  • Amine Bermak,
  • Abbes Amira,
  • Mohieddine Amor Benammar,
  • Debiao He,
  • Xiaojin Zhao

DOI
https://doi.org/10.1155/2014/861278
Journal volume & issue
Vol. 2014

Abstract

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Conventional two-step ADC for CMOS image sensor requires full resolution noise performance in the first stage single slope ADC, leading to high power consumption and large chip area. This paper presents an 11-bit two-step single slope/successive approximation register (SAR) ADC scheme for CMOS image sensor applications. The first stage single slope ADC generates a 3-bit data and 1 redundant bit. The redundant bit is combined with the following 8-bit SAR ADC output code using a proposed error correction algorithm. Instead of requiring full resolution noise performance, the first stage single slope circuit of the proposed ADC can tolerate up to 3.125% quantization noise. With the proposed error correction mechanism, the power consumption and chip area of the single slope ADC are significantly reduced. The prototype ADC is fabricated using 0.18 μm CMOS technology. The chip area of the proposed ADC is 7 μm × 500 μm. The measurement results show that the energy efficiency figure-of-merit (FOM) of the proposed ADC core is only 125 pJ/sample under 1.4 V power supply and the chip area efficiency is 84 k μm2·cycles/sample.