Circuit Diagram of Frequency Shift Demodulator Composed of CA3020 and MC723

Published:2011/6/21 6:26:00 Author:Vicky | Keyword: Frequency Shift Demodulator | From:SeekIC

IC1 is a broadband amplifier CA3020 which constitutes input stage of circuit. It’s differential out is connected to input ends J &K of IC2 (JK trigger MC723). Gate circuit IC3 constitutes monostable multivibrator, with a timing cycle equaling with 1/2 center frequency cycle. The input signal will strobe the trigger after going through monostable multivibrator. For example, If 2920Hz represents symbol and 2750Hz represents blank space, then the center frequency is 2835Hz, therefore the cycle of monostable multivibrator is 175μs. When the input signal is 2920Hz, and the trigger strobe end is J=1, and K=0, then the Q end’s output is 1”1” (representing symbole); when the input signal is 2750Hz, and the trigger strobe is J=0 and K=1, then the Q end’s output is “0” (representing space). The detection accuracy of the circuit is determined by the timing accuracy of monostable multivibrator multivibrator.



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