Design of low-Gm transconductors using varactor-based degeneration and linearization technique

Low-G_m transconductors are useful for designing low-frequency-cutoff filters and amplifiers used in processing of biomedical signals. However, designing fully integrated low-G_m transconductors presents a challenge due to limitations on the size of on-chip capacitors and resistors and due to requirements on the signal dynamic range and the linearity of the transconductor. In this paper we propose a novel method for designing low-G_m transconductors using a varactor-based degeneration and linearization technique. The technique uses negative feedback where a varactor changes the capacitance of a floating-gate to compensate for the change in the input voltage. This results in the degeneration of the transconductance and a differential configuration of the input stage linearizes and enhances the dynamic range of the transconductor. We verify and characterize the proposed approach using measurement results obtained from prototypes fabricated in a 0.5-μm CMOS process.