US 4,404,430 A · FM Stereo demodulation circuit with voltage dividing and multiplexing techniques

Abstract

An FM stereo demodulation circuit comprises a resistor voltage dividing network having a plurality of outputs; a first switch circuit having a plurality of analog switches which respectively couple the outputs of the voltage dividing network to a first output terminal; a second switch circuit having a plurality of analog switches which respectively couple the outputs of the voltage dividing network to a second output terminal; and a switch control circuit which sequentially enables the analog switches of the first and second switch circuits over one cycle period of a subscarrier signal in response to a pilot signal in an FM stereo composite signal. The circuits produce a staircase-wave multiplying signal having a waveshape which depends on the setting of the resistance values of resistors of the voltage dividing network. The FM stereo composite signal having the pilot signal therein or the pilot signal removed therefrom prior to demodulation is applied to the voltage dividing network so that the FM stereo composite signal is multiplied by the multiplying signal to accomplish the FM stereo demodulation.

Claims5

Dependent claims

An FM stereo demodulation circuit comprising:

a voltage dividing network connected to receive an FM stereo composite signal which contains a pilot signal of half the frequency of a subcarrier, said voltage dividing network having plurality of outputs which provide a plurality of different voltage levels;
a first switch circuit having a plurality of analog switches for respectively coupling said outputs of said voltage dividing network to a first output terminal;
a second switch circuit having a plurality of analog switches for respectively coupling said outputs of said voltage dividing network to a second output terminal;
and
analog switch control circuit means responsive to the pilot signal for scanning said analog switches of said first and second switch circuits such that said analog switches of each of said first and second switch circuits are sequentially enabled in a reciprocating manner over one cycle period of said subcarrier and a switch scan cycle of said first switch circuit is 180.degree. out of phase with that of said second switch circuit.

2 more elements

An FM stereo demodulation circuit comprising:

pilot signal eliminating circuit means for eliminating a pilot signal from an FM stereo composite signal which has the pilot signal of half a frequency of a subcarrier;
a voltage dividing network connected to receive an output signal of said pilot signal eliminating circuit means, said voltage dividing network having a plurality of outputs which provide a plurality of different voltage levels;
a first switch circuit having a plurality of analog switches for respectively coupling said outputs of said voltage dividing network to a first output terminal;
a second switch circuit having a plurality of analog switches for respectively coupling said outputs of said voltage dividing network to a second output terminal;
and
analog switch control circuit means responsive to the pilot signal for scanning said analog switches of said first and second switch circuit such that said analog switches of each of said first and second switch circuits are sequentially enabled in a reciprocating manner over one cycle period of said subcarrier and a switch scan cycle of said first switch circuit is 180.degree. out of phase with that of said second switch circuit.

3 more elements

Dependencies are inferred from the claim text.

FM Stereo demodulation circuit with voltage dividing and multiplexing techniques

Life of this patent

FM Stereo demodulation circuit with voltage dividing and multiplexing techniques

Life of this patent

Abstract

Claims5