A 174.8 dB FoMs CT-ΔΣ ADC with Integrated ISFET Sensor and Noise-Shaping Enhancement

In this paper, a continuous-time delta-sigma ADC with an integrated ISFET sensor has been proposed for high-resolution biochemical sensing applications. The ADC is designed as a 2nd-order system working under a 256 oversampling ratio, and the ISFET sensor performs as a part of the first gm-C integrator in the system loop. A 1-bit quantization and a DAC feedback, along with a lowpass RC filter, have been implemented to alleviate the linearity challenge. The phase-delay impact of the additional lowpass filter has been compensated by adjusting the weights of different signal paths in the loop. Besides, the noise-shaping effect can be even further enhanced by increasing the weight of the slow path. Simulated in a 180 nm CMOS process, the proposed ADC can achieve an SNDR of 98.78 dB with a bandwidth of 100Hz, consuming 2.5 uW from 1.8 V supply, resulting in 174.8 dB FoMs. This performance has included the ISFET sensor.