Design of a High Speed CMOS Image Sensor with a Hybrid Single-Slope Column ADC and a Finite State Machine

Abstract

In this paper, design of a CMOS Image sensor (CIS) with a hybrid single-slope ADC is presented. To obtain a small size and a high conversion rate CIS, no sampling capacitor structure is employed. This is implemented with a DC reference voltage and a single ramp generator. Further, by changing the input node of comparator, it reduces gain errors generated by a conventional 4-input comparator's differentia pair. The proposed hybrid ADC selects the resistor DAC's reference voltage controlled by a Finite State Machine(FSM), and converts the residual voltage with the single slope technique. Based on 1-Poly 5-Metal 90nm back side illuminated(BSI) CIS process, the chip satisfies 1920 x 1440 pixel resolution whose pitch is 1.4um and 1.75-Tr active pixel sensor(APS).