QUADRATURE DEMODULATING CIRCUIT

PURPOSE:To provide compact quadrature demodulating circuit which has the high demodulation sensitivity and a wide dynamic range by using the secondary LPF circuits consisting of the resistances, the capacitor elements, etc., and connected together in series and in an odd number of stages and a phase comparator circuit which compares the phase of an FM modulated wave signal with the phase of the output signal of a phase shifting circuit and then setting the phase shifted variable of the phase shifting circuit at -cXpi/2 (n: a odd number) with the center frequency of an FM modulated wave. CONSTITUTION:The input FM modulated wave signal is non-linearly amplified by a limiter amplifier 1, and this amplified output signal is divided and sent to a phase comparator circuit 5 and a phase shifting circuit 2. The signal supplied to the circuit 2 undergoes its phase shift by an extent equal to a phase angle accordant with the frequency of the output signal of the amplifier 1 and then is sent to a phase comparator circuit 4 via a limiter amplifier 3. The phase shifted variable of the circuit 2 is set at -cXpi/2 (n: a odd number) with the center frequency of an FM modulated wave. Thus a signal accordant with the output phase difference between both amplifiers 1 and 3 is sent to an LPF 5. Then the output signal is smoothed and the higher harmonic component is eliminated. Thus a demodulated wave DED is obtained.