| 摘要 |
PURPOSE:To obtain effectively an output of AM detection with an AM detecting circuit using a PLL circuit even in case the level is considerably low for a signal to receive an AM modulation. CONSTITUTION:A signal to receive an AM modulation which is supplied from a high frequency amplifier 2 is supplied to a phase comparator 4 through the 1st gate circuit 11. The output of the comparator 4 is fed to an AC amplifier 14. The output of the amplifier 14 is supplied to an LPF5 via the 2nd gate circuit 12. The circuit 11 samples the signal to receive an AM modulation with the oscillation output of an oscillator 13. A differential proportional to a signal component like a waveform B emerges at the output side of the comparator 4 even in case the level is considerably lower than the DC offset voltage for the signal to receive an AM modulation. This differential is amplified by the amplifier 14 up to such a level at which the DC offset voltage is neglected. This output of amplification (waveform C) undergoes a synchronizing waveform detection through the circuit 12 which is turned on and off synchronously with the circuit 11. Thus an output like a waveform D is obtained. |
