| 摘要 |
The signal control circuit utilizes an active, bandpass filter having a first resonant frequency virtually equal to the frequency of a first input signal selected thereby. An amplitude responsive circuit changes the resonant frequency of the filter to a second predetermined value during the times that the instantaneous magnitude of the output signal, provided in response to the first input signal, exceeds a threshold level. This action maintains the amplitude of the output signal at a substantially constant level even though the amplitude of the first input signal is varying. Moreover, the threshold level and second resonant frequency are chosen so that the phase difference between the first input signal and the output signal remains relatively constant even though the frequency of the first input signal is varying so that the output signal can be damped out by a second input signal having a selected phase relationship to the first input signal.
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