A Discrete-Time MOS Parametric Amplifier-Based Chopped Signal Demodulator

This article presents a discrete-time parametric amplifier (DTPA) as the signal demodulator for chopper amplifier. Unlike the conventional chopper, the DTPA demodulator features noise-efficient gain augmentation while demodulating the chopped signal. The demodulator also enables low-frequency noise cancellation during the inherent track-and-hold (T/H) process of the charge parametrization. The positive feedback loop and the dc servo loop are implemented for applications requiring larger input impedance and dc input offset cancellation using a bandpass transfer function. Design considerations for the DTPA-based demodulator circuit and the merits and demerits of the chopper-DTPA amplifier are discussed as well. The proposed design has been fabricated in a standard 180-nm CMOS technology node. The complete design occupies 0.127 mm² of the die area and consumes 2.4-μW power from a 1.5 V of VDD. The measurement results show that the DTPA demodulator provides 8-dB gain enhancement while improving on the prior art of T/H-based demodulator and the amplifier achieves input referred noise voltage of 2 μ Vrms in 143-Hz bandwidth.