| 摘要 |
A FSK signal demodulating integration-discharge circuit has a simple circuit configuration and utilizes an AC waveform of the FSK signal as a. control signal for a transistor gate. FSK signals are converted into rectangular-wave signals by the use of a limiter, before adding the rectangular-wave signal to an integrating capacitor C1 through a resistor. The capacitor C1 connects to a first transistor in parallel thereto, which is turned ON/OFF due to the rectangular-wave signal. The signal causes the capacitor C1 to be charged by the voltage corresponding to time length of a half cycle of a portion of positive voltage of the rectangular-wave signal, while causing the above capacitor C1 to discharge in terms of electric charge of the capacitor C1 by the voltage corresponding to time length of a half cycle of a portion of negative voltage of the rectangular-wave signal. Charged voltage from the capacitor C1 also feeds into a holding capacitor C2 through a second transistor. The second transistor is turned ON/OFF by the rectangular-wave signal. The holding capacitor C2 is charged at the same time the capacitor C1 is charged at the portion of a positive voltage, while at the next portion of negative voltage, the holding capacitor C2 is separated from the capacitor C1. Thus the capacitor C1 discharges, while the holding capacitor C2 holds charged voltage. This operation can obtain a hold voltage that is approximately inversely proportional to the frequency of the FSK signal.
|
