Abstract: A level detecting device 7 detects the input level of a tuner 11 and an external unit connection terminal 15. Corresponding to the detected result, a gain controlling circuit 8 controls the attenuation amount of a variable attenuator 5 so that the input level becomes a predetermined level. Switches 3 and 14 are controlled corresponding to the power ON/OFF states. In the power OFF state, the system connection terminal 2 and the external unit connection terminal 15 are connected. An up signal that is output from an up signal generating circuit is output from the system connection terminal 2 (to a transmission cable 1) through a branching device 4 that branches the up signal and the down signal.

Abstract: An RF AGC control circuit (47) gives a first initial voltage signal generated by a first initial level generating circuit (44) to an RF amplifier circuit (22) during a predetermined time duration T, when the channel selection signal was updated or when power supply is turned to on. After lapse of the predetermined time duration T, the RF AGC control circuit gives to the RF amplifier circuit a level difference signal representative of a level difference between output of an optimum level generating circuit (46) and output of a comparator (43). On the other hand, an IF AGC control circuit (48) gives a second initial voltage signal generated by a second initial level generating circuit (45) to an IF amplifier circuit 31 during the predetermined time duration T, when the channel selection signal was updated or when the power supply is turned to on. The IF AGC control circuit gives the output of the comparator to the IF amplifier circuit after lapse of the predetermined time duration T.

Abstract: A first clamp circuit clamps a tip of a synchronization signal of input video signal in accordance with a synchronization signal generated from a synchronization signal generator and outputs a clamped video signal. A level detector detects a level of a tip of a synchronization signal of the clamped video signal. A converter converts the detected level to a reference level signal so that the greater the detected level becomes, the smaller the reference level signal becomes. A second clamp circuit clamps the tip of the synchronization signal of the clamped video signal to the reference level signal and outputs an output video signal. Thus, the second clamp circuit compensates a remaining sag component included in the input video signal accurately.