FM stereo multiplex demodulator

Apparatus for demodulating an FM stereo multiplex signal, comprising:

• switching circuit means including double-balanced transistor elements connected to receive a switching signal having a frequency related to a carrier frequency of said FM stereo multiplex signal;
• first current mirror circuit receiving said FM stereo multiplex signal and producing therefrom said switching signal fed to said switching circuit, said switching circuit producing therefrom first and second output current signals;
• second and third current mirror circuits connected respectively to receive said first and second output current signals from said switching means for producing a respective output current signal therefrom;
• first signal difference circuit for producing an output current signal corresponding to a difference between said output current signal from said second current mirror circuit and said output current signal from said first current mirror circuit;
• and
• second signal difference circuit producing an output current signal corresponding to a difference between said output current signal from said third current mirror circuit and said output current signal from said first current mirror circuit.

A demodulator for producing left and right channel audio signals from a modulated composite FM stereo multiplex signal, comprising:

• a first current mirror circuit having an input side and an output side and receiving said composite FM stereo signal at said input side for producing a plurality of identical corresponding output current signals therefrom;
• means generating a switching signal having a frequency related to a carrier frequency of said composite FM stereo multiplex signal;
• switching circuit means receiving at least one of said plurality of output current signals from said current mirror circuit and receiving said switching signal for producing first and second composite output current signals;
• a second current mirror circuit having an input side receiving said first output current signal from said switching circuit for producing at said output side a corresponding current signal;
• a third current mirror circuit having an input side receiving said second output current signal from said switching means for producing at said output side a corresponding current signal;
• first current difference circuit for producing a current output signal corresponding to a difference between said output current signal from said second current mirror circuit and one of said plurality of output current signals from said output side of said first current mirror circuit;
• and
• second current difference circuit for producing a current output signal corresponding to a difference between an output current signal from said third current mirror circuit and one of said plurality of said current signals from said output side of said first current mirror circuit.