Current-feedback source-degenerated CMOS transconductor with very high linearity

Abstract

A highly linear current-feedback (CF) transconductor with resistive source-degeneration is developed in CMOS technology. It consists of a differential source follower cascaded with a classical source-degenerated transconductor with its drain current fed back to modulate the bias of the source follower for nonlinearity cancellation, yielding an overall linear transfer function in the circuit. Designed using a 0.35 µm CMOS process for a continuous-time delta-sigma application, the CF transconductor achieves the total harmonic distortion better than −80 dB up to 1 MHz for a 0.8 V input differential voltage while the supply voltage is 2.5 V and the power consumption is 3.4 mW.