| 摘要 |
PURPOSE:To automatically tune to original channel when returned to normal reception state, by clamping a defeat voltage and an error voltage at the input point of a channel selection circuit to a given voltage, when a test signal is input to a video amplifying circuit. CONSTITUTION:When a clamper circuit 100 is in operation, the upper limit of voltage of a signal line 9 is clamped to a voltage of the connection point 13 and the lower limit of the voltage of the signal line 9 is clamped to the voltage at the connection point 12. The voltage of the power supply 11 and each resistance value are designed so that the voltage clamped for the upper and lower limit can be a voltage near the objective voltage achieved for automatic fine tuning. Further, the voltage on the signal line 8 is clamped at lower than the voltage at the connection point 14. This lower voltage value corresponds to the voltage indicating the presence of the synchronizing signal at the detection circuit 6 and even if the defeat voltage indicating the absence of the synchronizing signal is output from the circuit 6, the upper limit of the voltage on the signal line 6 is clamped at the voltage at the connection point 14. |
