An amplifier having a switchable common gate gain buffer is disclosed. In an exemplary embodiment, an apparatus includes a plurality of selectable gain channels that provide constant input impedance at a common input to receive an input signal and generate an output signal having at least one of selected gain and current characteristics. At least two gain channels utilize transistors having different transconductance values. The apparatus also includes at least one impedance network coupled to at least one gain channel to provide the constant input impedance.