| 摘要 |
PURPOSE:To improve the demodulation 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:An FM intermediate frequency signal applied to an input terminal IN is branched into two paths P1, P2 and an FM signal via the P1 is applied to the multiplier 3 by a limiter amplifier 5 as the 1st input signal S1. After the FM signal via the P2 is phase-shifted by phi by a phase shifter 2, the result is applied to the multiplier 3 by a limiter amplifier 6 as the 2nd input signal S2. A part of an output signal S0 demodulated by the multiplier 3 is applied to an integration circuit 8, which detects the amount of phase shift phi and adjusts the amount of phase shift of the phase shifter 2 so that the value is converged to a prescribed value when the amount is shifted from the prescribed value. Since the phase shifter 2 is set to phase shift the FM signal by phi(=90 deg.) at the center frequency f0 of the inputted FM intermediate frequency signal, the integration circuit 8 detects the amount of shift from 90 deg. and operates that the amount is converged into 90 deg. at all times. |
