Patent ID: 7382189

Claim:
Apparatus comprising an amplifier circuit adapted to receive an input signal at least one input node (e.g., V 1,IN ) and present an amplified output signal at least one output node (e.g., V 1,OUT ), the amplifier circuit comprising at least one branch (e.g., 302 ) and current-source circuitry (e.g., I 1 , I 2 , S 3 ) adapted to provide a tail current to the at least one branch, each branch comprising: at least one load tank (e.g., 306 ); at least one input transistor (e.g., M 1 ) having a gate and coupled to the at least one load tank, wherein transconductance of the at least one input transistor is adapted to be altered to achieve two or more different gain settings for the amplifier circuit; and variable-impedance circuitry (e.g., R 2 , S 2 ) coupled between the input node and the gate of the input transistor, wherein the variable-impedance circuitry is adapted to be controlled to contribute any one of at least two different levels of impedance to overall input impedance of the amplifier circuit.