| 摘要 |
PURPOSE:To prevent the blocking of an AGC circuit by forcing electric current to flow through a capacitor, holding an AGC voltage, in an instantaneous time after the channel switching of a TV receiver. CONSTITUTION:To one terminal of capacitor 8, tuning voltage BT(a) or video detection output signal (b) is applied as a trigger signal. Then, since this tuning voltage and video detection output signal fall to potentials close to zero respectively, in channel switching a, transistor 3 is turned on-off by making use of the above- metioned phenomenon. In a normal reception state, transistor 3 and diode 5 are both cut off to exert no influence on an AGC circuit, but in channel switching (a), a low-level potential is applied to the base of transistor 3, which conducts. Its output appears at its collector and electric current is supplied to capacitor 2 via diode 5 to increase an AGC voltage while decreasing the gain, thereby preventing the blocking of the circuit. |
