| 摘要 |
PURPOSE:To exactly receive a broadcast signal whose frequency is weak, being in the proximity of a strong broadcast signal, by switching a time constant of an AGC circuit in a sweep period of receiving frequency, by a sweep control signal, so that it becomes smaller than a time constant in case when sweep has been stopped. CONSTITUTION:In the course of a receiving operation which has stopped usual sweep, capacity of an AGC circuit is the sum of capacity of a capacitor 9a and 9b, but in a channel selecting period, it becomes only capacity of the capacitor 9a, the time constant becomes small, and a response time is shortened. As a result, even when a weak broadcast signal exists in the proximity of a strong broadcast signal, the gain of a tuner and an IF amplifier can be quickly returned largely when the receiving frequency has been swept gradually from its strong broadcast signal, and its weak broadcast signal can also be fetched by an IF signal processing circuit 2. In this way, after the sweep has been stopped, the capacitor 9a and 9b of the AGC circuit are used again, and the stable receiving operation is continued by a large time constant. |
