Differential amplifier for balanced/unbalanced converter

A first field effect transistor receives an unbalanced signal from an input terminal at the gate thereof, and outputs a balanced signal from the drain thereof. A second field effect transistor has the gate thereof connected to the drain of the first field effect transistor and outputs a balanced signal from the drain thereof. The sources of the first field effect transistor and the second field effect transistor are connected to the drain of a third field effect transistor serving as a current source. The drain of the second field effect transistor is connected to the gate of the first field effect transistor via a first resistor. A first output terminal is connected between the drain of the first field effect transistor and the first resistor, and a second output terminal is connected between the drain of the second field effect transistor and a second resistor. Balanced signals produced by conversion in the first field effect transistor and the second field effect transistor are output from the output terminals. The drain of the second field effect transistor is connected to the gate of the first field effect transistor via a feedback resistor.