Tunable CMOS Pseudo-Resistors for Resistances of Hundreds of GΩ

This paper presents the design of tunable CMOS pseudo-resistors aimed at achieving large and predictable resistance values. Instrumental to the proposed pseudo-resistor is the design of current sources of extremely low currents and transistors operating in subthreshold. The effects of the leakage currents of reverse-biased pn-junctions on the pseudo-resistor resistance are also evaluated. The proposed pseudo-resistor circuit was validated while in use as part of a filter integrated in a 180 nm CMOS process. Pseudo-resistors with resistances between 180
$\text{G}\Omega $
and 700
$\text{G}\Omega $
were employed to obtain low-frequency poles of a band-pass filter adjustable from 0.6 Hz to 2 Hz.