Low-Power Capacitively Coupled AC Amplifiers With Tunable Ultra Low-Frequency Operation

This paper proposes two novel and compact low-power tunable AC amplifiers with ultra-low high-pass corner frequency. The circuits are based on alternative AC capacitively coupled feedback topologies using novel implementations leading to better performance in terms of area, power and noise efficiency. This is accomplished by a combination of actively boosting the resistive value of a pseudo-resistor (allowing more than two decades of tuning) and an optimization of the active devices required. Measurement results from a fabricated prototype using a 0.18~\mu \text{m} technology are provided to demonstrate the technique. The proposed amplifiers can provide tunable high-pass corner frequencies ranging from 31 mHz to 7 Hz, with power consumption as low as 0.425~\mu \text{W} , CMRR of 84 dB, 0.1 mm2 area, 39.7 dB gain, and integrated IRN of 2.42~\mu \text{V}_{\mathrm {rms}} .