High-value tunable pseudo-resistors design

Pseudo-resistor circuits are used to mimic large value resistors and base their success on the reduction of occupied areas with respect to physical devices of equal value. This article presents an optimized architecture of pseudo-resistor, made in standard CMOS 0.35 um technology to bias a low-noise transimpedance amplifier for high-sensitivity applications in the frequency range 100 kHz - 10 MHz. The architecture was selected after a critical review of the different topologies to implement high-value resistances with MOSFET transistors, considering their performance in terms of linearity of response, symmetric dynamic range, frequency behavior, and simplicity of realization. The resulting circuit consumes an area of 0.017 mm^2 and features a tunable resistance from 20 MOhm to 20 GOhm, dynamic offset reduction due to a more than linear I-V curve, and a high-frequency noise well below the one of a physical resistor of equal value. This latter aspect highlights the larger perspective of pseudo-resistors as building blocks in very low-noise applications in addition to the advantage in occupied areas they provide.