A Programmable Four-Order Power-Efficient Active RC Low-Pass Filter

This article proposes a programmable low-power active RC low-pass filter circuit. The architecture of the filter is a fourth-order Butterworth composed of two cascaded Tomas II second-order low-pass filters. As the core component of the filter, the operational amplifier is designed with a second-order fully differential Miller compensation amplifier. Additionally, we introduce a novel programmable resistor array to enhance the filter's programmability. The amplifier gain is 49.8dB, a phase margin of 61.1° and a unity gain bandwidth of 114 MHz, which can effectively meet the requirements of filter application. The proposed programmable resistor array module introduces a new resistor switch array architecture that simplifies logical operations in the filter and significantly reduces power consumption and layout area due to the smaller total resistance value used. The final simulation result shows that, taking 180 nm/1.8 V standard CMOS technology, the power consumption of the overall filter circuit is only 0.53 mW with a chip area of approximately 0.22 mm². The 2-bit programmable filter can effectively realize four cut-off frequencies of 250 kHz, 500 kHz, 1 MHz and 2 MHz, which meets the demands of pint-size and multifunctionality applications of analogue signal processing.