PURPOSE: To reduce the drift of the local oscillation frequency and also to minimize the undesired radiation by providing a control input terminal to switch the active and inactive states of a buffer amplifier.

CONSTITUTION: When a TV tuner IC is applied to a frequency synthesizer system, a pre-scaler buffer 5 becomes active when the voltage E1 is applied to a control input terminal 13 to secure a high level. Meanwhile the buffer 5 becomes inactive and consumes no electric power when the terminal 13 is grounded to secure a low level if the tuner IC is applied to a voltage synthesizer system. Thus it is possible to reduce the drift of the local oscillation frequency and to minimize the undesired radiation by using the terminal 13 to switch the active/inactive states of the buffer 5.