Abstract: A transimpedance amplifier is configured for high gain, high bandwidth, low noise and stable operation. The transimpedance amplifier includes an amplifier with an output coupled to a load for setting the gain of the amplifier. The input of the amplifier serves as the input to the transimpedance amplifier and is substantially isolated from the load. The input impedance of the transimpedance amplifier is controlled as a function of the applied input signal. Preferably, the amplifier is a field effect transistor (FET). A feedback amplifier is used to control the input impedance. Automatic gain control is used to keep the amplifier out of saturation.