| 摘要 |
An FM discriminator useful in a modem circuit includes a tank circuit coupled to an input receiving an FSK input signal. The FSK input signal is resistively coupled to an input of an operational amplifier having its output also coupled to that input. The other input of the operational amplifier is connected to the tank circuit and to an input of a comparator. The other input of the comparator is connected to the output of a circuit which produces a signal that lags by 90 degrees the signal produced by the tank circuit. The output of the comparator is used to synchronously chop the output signal of the first operational amplifier in such a way as to pass the operational amplifier output signal when the comparator output signal is a "1" and to invert the operational amplifier output signal when the comparator output signal is a "0". The tank circuit resonates at a frequency between the "0" and "1" frequencies of the FSK signal and, in combination with the operational amplifier, causes attenuation of components of the FSK input signal which are at the resonant frequency.
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