A pseudo-resistor configuration exhibiting linear behaviour over a broad voltage range

In the design of physiological signal analogue front-end interface circuits, the use of pF-level capacitors and GΩ-level resistors is essential for the construction of frequency-adjustable filters capable of covering the lower frequency and cutoff frequency ranges. Nevertheless, it is not feasible to integrate passive resistors with such high resistance values within an integrated circuit. To address this challenge, a novel pseudo-resistor (PR) scheme, which combines the advantages of ultrahigh resistance value and small footprint, has been adopted, thereby opening up a new path for the design of low-frequency reconfigurable filters. This paper presents a pseudo-resistor circuit design based on the 180nm BCD process, which significantly enhances the robustness of the pseudo-resistor to process, voltage and temperature variations by introducing an innovative bias current circuit scheme. The simulation test results demonstrate that the pseudo-resistor exhibits excellent linearity of approximately 1.5% over a broad input voltage range of -2.5V to +2.5V, with minimal variation in resistance value. This attribute renders it an optimal choice for the construction of active RC filters for extremely low frequencies, as well as the high-resistance resistors necessitated by bio-amplifiers.