PHASE SHIFT SYNERGETIC FM DEMODULATOR

摘要

PURPOSE:To improve the demodulating efficiency by keeping a phase difference of 90 deg. at the center frequency between two FM intermediate frequency signals inputted to a multiplier to balance output voltages and the demodulating operation. CONSTITUTION:A rectangular wave generating circuit 5 to which an FM intermediate frequency rectangular wave signal S1 converted into a rectangular wave by a limiter amplifier 1 is inputted is triggered by the rising of the S1 and outputs a rectangular wave signal S3 taking a T/2 of the center frequency f0 of the S1 as a width of rectangular wave. Similarly, a rectangular wave generating circuit 6 is triggered by the falling of the S1 and outputs a rectangular wave signal S3 taking a T/2 of the center frequency f0 of the S1 as a width of rectangular wave. An OR circuit 7 outputs a rectangular wave signal S5 and an exclusive OR circuit 8 outputs a rectangular wave signal S2 by using the S5 and S1. Since the phase shifter 2 outputs the rectangular wave signal S2 by phase-shifting the FM intermediate frequency rectangular wave signal S1 by 90 deg. to the multiplier 3 and the average value of an output signal S0 of the multiplier 3 is zero, a balanced output voltage at the center frequency f0 is obtained.