80dB dynamic range 100KHz bandwidth inverter-based ΣΔ ADC for CMOS image sensor

A sigma delta (ΣΔ) ADC for sensing application is presented in this paper. Several techniques are adopted to implement a low power high dynamic range ADC. Firstly, a single-stage inverter replaces the commonly used differential amplifier, in order to reduce the static current. Secondly, the normal NMOS transistor in the inverter stage is replaced by a high threshold device. As a result, with the same transistor size and supply voltage, the gain of the inverter can be enhanced while the short circuit current can be reduced. Thirdly, the charge leakage due to the forward-based parasitic diode is eliminated by using a charge protection switch and rearranged reference scheme. The proposed ΣΔ ADC is implemented and fabricated using TSMC 0.18μm technology. The simulation result shows that for a 1.8V supply, 25MHz sampling frequency and 125 oversampling ratio, the power consumption is 63.7μW and 116μW, dynamic range is 80dB and 83dB, the ENOB is 11.5 and 11.7bit for a single-ended and a pseudo-differential configurations, respectively. The presented ADC scheme can be applied in a Full HD image sensor running at up to 50 frames/s.