A Design of Variable-Cutoff-Frequency CMOS High-Pass Filter using Low-Bias Current Control

Abstract

This paper presents a variable-cutoff-frequency CMOS high-pass filter, which is designed for low-power analog front-end applications. The filter employs a weak-inversion MOSFET network to synthesize a GΩ-range equivalent resistance, enabling low-frequency operation without relying on large on-chip resistors. The cutoff frequency is adjusted by a low-bias current control scheme consisting of four selectable 300 pA branches, which tune the effective equivalent resistance while maintaining minimal power consumption. A comparator utilizes a folded cascode stage for common-mode stabilization and accurate bias control. Implemented in a 180 nm CMOS technology, the proposed prototype occupies 0.0045 mm2, consumes 0.749 µW, and provides five programmable high-pass corner frequencies ranging from 50 Hz to 100 kHz. The aforementioned features make the proposed architecture suitable for compact, energy-efficient front-end systems requiring reliable and tunable high-pass filtering