Replica bias circuit for common-source amplifier

Abstract

A replica bias circuit to set the current of common-source amplifier to reduce the gain variations across process, voltage, and temperature (PVT) changes is proposed. The gain of a common-source amplifier is set by the load resistor and transistor transconductance which is set proportional to a resistor using a constant-gm bias circuit. The success of constant-gm biasing depends on the accuracy of copying of generated current to the transistor. The leakage current at the transistor gate due to the electrostatic discharge protection diodes prevents the matching of the common source transistor current to the constant-gm circuit current. A low-power replica of the common-source amplifier is used to determine the current error which is minimized using a feedback circuit. Corner simulations indicate that gain variation across PVT reduced to +/- 1.9 dB using the proposed biasing method as opposed to +/- 9.9 dB for traditional biasing method for 1 mu A leakage current. Monte Carlo simulations with process and mismatch indicate that the standard deviation of the gain is reduced to 0.34 dB from 3.57 dB.