Precise and Tunable TΩ Pseudo-Resistors Based on Process-Independent pA-level Current Sources and DACs

Pseudo-resistors are employed as substitutes for poly resistors in scenarios necessitating exceedingly high resistance values. This paper presents the design of a tunable hundreds-GΩ pseudo-resistor achieving 6.26% relative standard deviation in a 180-nm CMOS technology. The pseudo-resistor is used as a feedback resistor in a capacitively-coupled instrumentation amplifier to realize sub-Hz high-pass corners. A self-biased current source along with a dedicated pico-ampere-level current mirror DAC is employed for tuning the pseudo-resistor. The proposed current mirror DAC design reduces the impact of unwanted leakage currents to achieve improved tuning accuracy. Measurement results show that the achieved resistances are linearly dependent on the control code with a span from 230 GΩ to 845 GΩ. The capacitively-coupled instrumentation amplifier with the proposed pseudo-resistor technology is successfully tested in a Lewis-lead ECG recording experiment.