AM stereo signal demodulation circuit

Claim 1

A stereo signal demodulation circuit comprising a first differential circuit including first and second transistors having emitters connected commonly; means for applying an input stereo signal to be demodulated between the bases of said first and second transistors; a second differential circuit including third and fourth transistors having their emitters commonly connected, said signal to be demodulated being applied between bases of said third and fourth transistors; a third differential circuit including fifth and sixth transistors having their respective emitters connected to the collector of said first transistor; a fourth differential circuit including seventh and eighth transistors having their respective emitters connected to the collector of said second transistor; a fifth differential circuit including ninth and tenth transistors having their respective emitters connected to the collector of said third transistor; and a sixth differential circuit including eleventh and twelfth transistors having their respective emitters connected to collector of said fourth transistor; wherein, when a first signal having frequency and phase corresponding to that of a first carrier signal of said stereo signal to be demodulated is applied between the bases of said fifth and sixth transistors and between the bases of said seventh and said eighth transistors, and when a second signal having frequency and phase corresponding to a second carrier signal out of phase by 90° from said first carrier signal is applied between the bases of said ninth and tenth transistors and between the bases of said eleventh and twelfth transistors, a first output signal containing a first channel signal is derived between a common collector connection of said fifth and eighth transistors and a common collector connection of said sixth and said seventh transistors, and a second output signal containing a second channel signal is derived between a common collector connection of said ninth and twelfth transistors and a common collector connection of said tenth and eleventh transistors.

Claim 15

A method of demodulating a stereo signal having the form: e.sub.s =[{1+k(L.sub.(t) +R.sub.(t))} cos ω.sub.c t+k{L.sub.(t) -R.sub.(t) } cos (ω.sub.c t+π/2)] cos φ, where, φ=tan.sup.-1 k{L.sub.(t) -R.sub.(t) }/[1+k{L.sub.(t) +R.sub.(t) }] where L.sub.(t) and R.sub.(t) are the left channel signal and right channel signal, respectively; ω c is the angular frequency of a carrier signal; and k is a modulation factor, comprising the steps of: dividing the stereo signal by a signal of the form cos φ; and separately multiplying the divided stereo signal by signals having the forms cos (ω c t+π/4) and cos (ω c t-π/4), respectively, to produce first and second components of the stereo signal which contain the right and left channel audio signals, respectively, as full wave rectified signals.

Claim 16

A method of demodulating a stereo signal having the form: e.sub.s =[{1+k(L.sub.(t) +R.sub.(t))} cos ω.sub.c t+k{L.sub.(t) -R.sub.(t) } cos (ω.sub.c t+π/2)] cos φ, where, φ=tan.sup.-1 k{L.sub.(t) -R.sub.(t) }/[1+k{L.sub.(t) +R.sub.(t) }] where L.sub.(t) and R.sub.(t) are the left channel signal and right channel signal, respectively; ω c is the angular frequency of a carrier signal; and k is a modulation factor, comprising the steps of: dividing the stereo signal by a signal of the form cos φ; and separately multiplying the divided stereo signal by signals having the forms cos (ω c t+π/4) and cos (ω c t-π/4), respectively, to produce first and second components of the stereo signal which contain the right and left channel audio signals, respectively, as full wave rectified signals.