A 187.5µVrms-read-noise 51mW 1.4Mpixel CMOS image sensor with PMOSCAP column CDS and 10b self-differential offset-cancelled pipeline SAR-ADC

Abstract

Low-power and small-area implementations are essential in the mobile-phone market. Serial signal-processing architectures, in which signal-processing circuits such as a programmable-gain amplifier (PGA) and an ADC can be shared by column-level correlated double sampling (CDS) circuits, promise to reduce chip size and power consumption. However, conventional column CDS circuits composed of linear capacitors or NMOS capacitors (NMOSCAPs) with output buffers (OBUFs) still occupy a large footprint. In this work, to reduce the area and the power consumption of column CDS circuits while keeping high linearity, 1.5V PMOS capacitors (PMOSCAPs) are employed. These capacitors work as low-cost sample-and-hold (S/H) capacitors as well as voltage level-shifters by using body-terminal control. To reduce the power consumption of the ADC, instead of a conventional pipeline ADC, we propose a 10b self-differential offset-cancelled pipeline SAR-ADC. It operates with the reference voltage of the ADC's half full-scale voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fs</sub> ), leading to a reduction of 80% switching power and 50% capacitor DAC (CDAC) area in the ADC. A black-level correction function is built in the ADC without any additional DACs. The proof-of-concept circuits are implemented in a 1.4Mpixel CMOS image sensor that consumes 51.0mW with a frame rate of 17fps and a read noise of 187.5μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> at 8.1× analog gain.