| 摘要 |
PURPOSE:To eliminate surely pulse noise by locking a detected signal obtained by a noise detecting means at a PLL circuit and waveform-shaping a detected signal deformed by an oscillating signal whose phase is coincident with that of the detected signal. CONSTITUTION:A phase comparator 12 compares the phase of a blanking pulse fg produced by a circuit 11 with the phase of the oscillating signal of a voltage controlled oscillator (VCO)14 and an error signal is outputted from a low pass filter (LPF)13 to the VCO14. The oscillated signal from the VCO14 is shaped by a pulse shaping circuit 16 and transmitted to the control side of a gate circuit 5 as a blanking pulse f'g. When the VCO14 is started by a noise blanker on/off signal at a terminal 15, an input signal fi including pulse noise via an intermediate frequency amplifier 8 is outputted as a noise detecting signal from a detector 9. The gain of the amplifier 8 in this case is controlled by an AGC10. Even if the AGC voltage is fluctuated and the width of the pulse fg is narrowed by phasing, etc., since the waveform of the oscillated signal of the VCO14 locked by the PLL circuit is unchanged, the width of the pulse f'g is kept constant and the control of the gate circuit 5 is guaranteed. |
