| 摘要 |
An integrated circuit FSK transmitter and receiver combination form a modem for receiving and transmitting FSK signals. The FSK transmitter has a square wave generator (11, 12, 13) for providing a clock output at a "mark" frequency or at a "space" frequency within a first frequency band. This clock output is shaped through a bandpass filter, (15, 16) shared with the FSK receiver, to provide an FSK output signal which is output through a low pass filter (20). The input FSK signal is received through a low pass filter (19) and then filtered through the band pass filter (15, 16). One section of the band passfilter (15, 16) accommodates the clock output while another section accommodates the FSK input, including an automatic gain control circuit (17). The band pass filter is connected to an integrated circuit demodulator (18) to provide a filtered sine wave thereto at either a mark or a space frequency within a second frequency band. The demodulator determines whether the sine wave is at a mark or a space frequency. |
