Signal processing circuit for switch capable of reducing insertion loss.

A high frequency power amplifier is implemented by a GaAs FET and is supplied with a positive and a negative power supply. The amplifier amplifies the power of an input signal and delivers the amplified signal to a high frequency switch (1). The high frequency switch is supplied with switch control voltages in the form of the positive and negative voltages. Since the switch control voltages are implemented as the positive and negative voltages, a great difference in level between the switch control voltages is achievable which improves insertion loss. While the high frequency switch may also be implemented by GaAs FETs, the insertion loss will be further reduced if the negative voltage is applied to the high frequency switch only during transmission. In this case, current consumption will also be reduced if the generation of the negative voltage is controlled at the negative voltage source side.