FM demodulator circuits

Claim 2

Apparatus For demodulating first and second FM signals contained in a composite signal, said composite signal characterized in that said first and second FM signals each have their own separate and independent carrier frequency, comprising: a. first means for providing at an output a third FM signal substantially related to said first FM signal but of opposite phase, b. second means for providing at an output a fourth FM signal substantially related to said second FM signal but of opposite phase, and c. means responsive to said composite signal and said third and fourth signals to provide at one output said first FM signal and at separate output said second FM signal.

Claim 3

The apparatus according to claim 1 wherein said first and second means each include a phase locked loop, each loop including a voltage controlled oscillator, a phase detector and a loop filter arranged in a demodulator configuration.

Claim 4

The apparatus according to claim 1 wherein said means responsive to said composite signal and said third and fourth signals comprises a first and a second adder circuit, each having one input terminal responsive to said composite signal, said first adder having another input terminal responsive to said third signal to provide at an output said second FM signal, said second adder having another input terminal responsive to said fourth FM signal to provide at an output said first FM signal.

Claim 5

The apparatus according to claim 2 further including a first feedback path coupling said first loop to said second loop and a second feedback path coupling said second loop to said first loop.

Claim 6

Apparatus for demodulating first and second FM signals contained in a composite signal, said composite signals characterized in that said first and second FM signals each have their own separate and independent carrier frequency, comprising: a. first and second phase locked loop each capable of responding to said first and second FM signals, b. first and second adding means each having first and second input terminals and an output terminal, said output terminal of one of said adding means coupled to one of said loops and said output terminal of said other adding means coupled to said other loop, one of said input terminals of each responsive to said composite signal and said other terminal coupled to a different one of said phase locked loops to cause said first loop to demodulate only said first FM signal and said second loop to demodulate only said second FM signal, and c. means coupled to said first and second loops for utilizing said first and second FM signals independently of one another.

Claim 7

Apparatus for demodulating first and second FM signals contained in a composite signal, said composite signals characterized in that said first and second FM signals each have their own separate and independent carrier frequency, comprising: a. first and second phase locked loop each capable of responding to said first and second FM signals, b. first and second adding means each having first and second input terminals and an output terminal, said output terminal of one of said adding means coupled to one of said loops and said output terminal of said other adding means coupled to said other loop, one of said input terminals of each responsive to said composite signal and said other terminal coupled to a different one of said phase locked loops to cause said first loop to demodulate only said first FM signal and said second loop to demodulate only said second FM signal, and c. means coupled to said first and second loops for utilizing said first and second FM signals independently of one another.

Claim 8

Apparatus for responding to a first FM signal in the presence of a second and interfering FM signal wherein said second interfering FM signal may have a carrier frequency substantially equal to the carrier of said first FM signal, comprising: a. first and second phase locked loop circuits, said first loop circuit including a first oscillator capable of providing a first signal having a frequency selected according to said first FM signal, said second loop including a second oscillator capable of providing a second signal having a frequency selected according to said second FM signal. b. a first and second summing circuit having a common input terminal responsive to said first and second FM signals and each having another input terminal, each of said summing circuits having an output terminal, said output terminal of said first summing circuit coupled to said first phase locked loop and said output of said second summing circuit coupled to said second phase locked loop, c. first means for applying the oscillator signal of said first loop circuit to said input terminal of said second summing circuit to cause said summing circuit to provide said first FM signal at an output, and d. second means for applying the oscillator signal of said second loop circuit to said input terminal of said first sumMing circuit to cause said summing circuit to provide said second FM signal at an output.

Claim 9

Apparatus for responding to a first FM signal in the presence of a second and interfering FM signal wherein said second interfering FM signal may have a carrier frequency substantially equal to the carrier of said first FM signal, comprising: a. first and second phase locked loop circuits, said first loop circuit including a first oscillator capable of providing a first signal having a frequency selected according to said first FM signal, said second loop including a second oscillator capable of providing a second signal having a frequency selected according to said second FM signal. b. a first and second summing circuit having a common input terminal responsive to said first and second FM signals and each having another input terminal, each of said summing circuits having an output terminal, said output terminal of said first summing circuit coupled to said first phase locked loop and said output of said second summing circuit coupled to said second phase locked loop, c. first means for applying the oscillator signal of said first loop circuit to said input terminal of said second summing circuit to cause said summing circuit to provide said first FM signal at an output, and d. second means for applying the oscillator signal of said second loop circuit to said input terminal of said first sumMing circuit to cause said summing circuit to provide said second FM signal at an output.

Claim 10

The apparatus according to claim 6 wherein said first and second means include a phase shifting network capable of shifting said oscillator signals a predetermined number of degrees.

Claim 11

A demodulator for demodulating a first and second FM signal contained in a composite signal, said composite signal characterized in that first and second FM signals each have their own separate and independent carrier frequency, comprising: a. a first adding circuit having first and second input terminals and an output terminal, said first input terminal responsive to said composite signal, b. a second adding circuit having first and second input terminals and an output terminal, said first input terminal responsive to said composite signal, c. a first phase locked loop including a first phase detector having one input coupled to the output of said first adding circuit and another input responsive to a first oscillator included in said loop, said loop capable of providing at an output a demodulated version of said first FM signal, d. a second phase locked loop including a second phase detector having one input coupled to the output of said second adding circuit and another input responsive to a second oscillator included in said loop, said loop capable of providing at an output a demodulated version of said second FM signal, e. first means coupling said first oscillator to said second input terminal of said second adding circuit to cause said second loop to provide said demodulated second FM signal, and f. second means coupling said second oscillator to said second input terminal of said first adding circuit and cause said first loop to provide said demodulated first FM signal.

Claim 12

A demodulator for demodulating a first and second FM signal contained in a composite signal, said composite signal characterized in that first and second FM signals each have their own separate and independent carrier frequency, comprising: a. a first adding circuit having first and second input terminals and an output terminal, said first input terminal responsive to said composite signal, b. a second adding circuit having first and second input terminals and an output terminal, said first input terminal responsive to said composite signal, c. a first phase locked loop including a first phase detector having one input coupled to the output of said first adding circuit and another input responsive to a first oscillator included in said loop, said loop capable of providing at an output a demodulated version of said first FM signal, d. a second phase locked loop including a second phase detector having one input coupled to the output of said second adding circuit and another input responsive to a second oscillator included in said loop, said loop capable of providing at an output a demodulated version of said second FM signal, e. first means coupling said first oscillator to said second input terminal of said second adding circuit to cause said second loop to provide said demodulated second FM signal, and f. second means coupling said second oscillator to said second input terminal of said first adding circuit and cause said first loop to provide said demodulated first FM signal.

Claim 13

The demodulator according to claim 8 wherein said first and second means include a phase shift network for shifting the phase of said oscillator signal a predetermined number of degrees.