Abstract

A novel approach for highly linear automatic gain control (AGC) in small-signal ampli¯ers is presented in this paper. A HEMT based topology was implemented, biasing the transistor in the transition between the saturated and linear operation regions. Gain control with low distortion is achieved by simultaneous adjustments of the gate to source (Vgs) and drain to source (Vds) voltages, along the line where the second derivative of the transconductance (Gm3) has a null. Comparatively to the traditional approach, with the transistor biased in the saturated region, this ampli¯er has better intermodulation behavior and e±ciency, without important reduction in the gain control range.