Stereo demodulation system for an FM stereo broadcast receiver

A stereo demodulation system for an FM stereo broadcast receiver in which a signal for switching and decoding a received stereo composite signal is produced in a demodulator, said system comprising:

• a voltage controlled oscillator which produces a signal of a specific frequency (f.sub.vco),
• frequency dividing means for receiving the output signal of said voltage controlled oscillator and producing a first switching signal of 1/m frequency (f.sub.vco /m) of said specific frequency and a second switching signal of 1/l frequency (f.sub.vco /l) of said specific frequency,
• a phase comparator for phase comparing a further frequency divided signal of said first switching signal with a pilot signal contained in the received stereo composite signal,
• a low pass filter for filtering the output signal of said phase comparator and feeding back the thus filtered signal to said voltage controlled oscillator so that said voltage controlled oscillator, said frequency dividing means, said phase comparator and said low pass filter constituting a phase locked loop,
• a first switch and decoder circuit for switching and decoding said stereo composite signal by said 1/m frequency (f.sub.vco /m) signal produced from said frequency dividing means,
• a second switch and decoder circuit for switching and decoding said stereo composite signal by an output signal of 1/l frequency (f.sub.vco /l) of said predetermined frequency produced from said frequency dividing means, and
• an addition/subtraction circuit for adding or subtracting the output signals of said first and second switch and decoder circuit so that the signal component in the output signal of said first switch and decoder circuit, which component is a product of the harmonic frequency component of the subcarrier signal and the stereo composite signal, is cancelled by the signal component in the output signal of said second switch and decoder circuit, which component is a product of the fundamental frequency component of the switching signal and the stereo composite signal,
• characterized in that:
• said first switching signal of 1/m frequency (f.sub.vco /m) and said second switching signal of 1/l frequency (f.sub.vco /l) are produced by said frequency dividing means with the fixed phase relationship between said first and second switching signals.