# US 5,706,350 A · Stereophonic decoder

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- Number: US 5,706,350 A
- Document ID: US5706350A
- Status: Granted
- Kind: A
- Application number: 08/706,713
- Filed: 1996-09-06
- Granted: 1998-01-06
- Earliest claimed: 1995-09-08
- Assignees: Kabushiki Kaisha Toshiba
- Inventors: Atsusi Ogawa; Tsuneyuki Murayama
- Web page: https://patentgrep.com/patent/US5706350A

## CPC

- H04H 20/49: for AM stereophonic broadcast systems
- Y02D 30/70: in wireless communication networks
- H04H: BROADCAST COMMUNICATION (multiplex communication H04J; pictorial communication aspects of broadcast systems H04N)
- Y02D: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE

## Abstract

A compatible quadrature type AM sterophobic decoder including an enveolpe detector for providing a current output signal and a combination of a VCA and a synchronous detector for providing a current output signal. The combination of the VCA and the synchronous detector is controlled by a feedback signal from an adder which adds the current output signal of the envelope detector and the inverting current output signal of the conbination of the VCA and the synchronous detector.

## Claims

### Claim 1

A compatible quadrature AM stereophonic decoder, comprising:
an envelope detector for detecting an IF signal of a compatible AM signal and providing a compatible monophonic (1+L+R) signal to a matrix circuit; and
a combination of a VCA circuit and a synchronous detector for detecting the IF signal and providing a quadrature monophonic (L-R) signal to the matrix circuit for separating and demodulating left and right channel signals;
wherein:
the envelope detector is comprised of a current output type detector and the combination of the VCA circuit and the synchronous detector is also comprised so as to provide current output signals; and
the VCA circuit is controlled by a feedback signal which comes from an adder for adding the current output of the envelope detector and the current output of the combination of the VCA circuit and another synchronous detector in order to maintain a same current level between the signals to the matrix circuit.

### Claim 2

A compatible quadrature type AM stereophonic decoder for processing a received AM stereophonic signal and providing a pair of L and R signals through a matrix circuit, comprising:
an envelope detector;
an amplifying stage for providing an IF signal of the received AM stereophonic signal to the envelope detector and a VCA circuit;
the envelope detector for supplying a compatible monophonic (1+L+R) current signal which corresponding to a modulated component of the IF signal;
the VCA circuit for supplying a voltage control amplifying signal in response to an input of the IF signal;
an in-phase synchronous detector for detecting a carrier signal of the IF signal with a first reference signal which is in-phase to the carrier signal of IF signal and supplying an inverted -(1+L+R) current signal;
a quadrature synchronous detector for detecting a carrier signal of the IF signal with a second reference signal which is quadrature to the carrier signal of IF signal and supplying a quadrature (L-R) current signal;
an adder for adding the output current signal of the envelope detector and the output current signal of the in-phase synchronous detector; and
an integrator for supplying a feedback voltage signal of the output current from the adder to the VCA.

### Claim 3 (depends on 2)

A compatible quadrature type AM stereophonic decoder according to claim 2, wherein:
the integrator comprises of a NPN transistor of which emitter is coupled to an earth node and, a resistor element and a capacitor element which are parallel coupled;
a base of the NPN transistor receives the output current of the adder;
a constant current source is coupled between a source voltage and a collector of the NPN transistor; and
the collector of the NPN transistor is coupled to the second input of the VCA for supplying the feedback signal from the adder.

### Claim 4 (depends on 2)

A compatible quadrature type AM stereophonic decoder according to claim 2, wherein:
the in-phase synchronous detector and the quadrature synchronous detector are commonly comprised of two pair of differential amplifiers of NPN transistors of which bases are coupled to the output of the VCA circuit;
each of the differential amplifier comprises of a pair of NPN transistors of which emitters are commonly coupled with each other; and
the first and second reference signals are respectively supplied to the respective commonly coupled emitters of the differential amplifier.

### Claim 5 (depends on 2)

A compatible quadrature type AM stereophonic decoder according to claim 2, wherein:
the matrix circuit comprises of a NPN transistor, a constant current source and a resistor element;
a collector of the NPN transistor is coupled to a source voltage through the constant current source;
an emitter of the NPN transistor is coupled to an earth potential node;
a base of the NPN transistor receives the compatible monophonic signal or the quadrature monophonic signal; and
the separated L or R channel signal is supplied through an output terminal which is coupled to the collector of the NPN transistor.

### Claim 6

A compatible quadrature type AM stereophonic decoder for processing a received AM stereophonic signal and providing a pair of L and R signals through a matrix circuit, comprising:
an amplifying stage for providing an IF signal of the received AM stereophonic signal;
an envelope detector for supplying a compatible monophonic (1+L+R) current signal which corresponding to a modulated component of the IF signal;
a VCA circuit for supplying a voltage control amplifying signal in response to an input of the IF signal;
an in-phase synchronous detector for detecting a carrier signal of the IF signal with a first reference signal which is in-phase to the carrier signal of IF signal;
a first VCA circuit for receiving an output of the in-phase synchronous detector and supplying an inverted -(1+L+R) current signal;
a quadrature synchronous detector for detecting a carrier signal of the IF signal with a second reference signal which is quadrature to the carrier signal of IF signal;
a second VCA circuit for receiving an output of the quadrature synchronous detector and supplying a quadrature (L-R) current signal;
an adder for adding the output current signal of the envelope detector and the output current signal of the first VCA circuit; and
an integrator for supplying a feedback voltage signal of the output current from the adder to the first and second VCA circuits.

### Claim 7 (depends on 6)

A compatible quadrature type AM stereophonic decoder according to claim 6, wherein:
the first and second VCA circuits are commonly comprised of a first and a second differential amplifiers, each of the diffential amplifiers is comprised of two NPN transistors in which emittors are commonly mirror-coupled, and a first and a second base of the transistors in the first differential amplifier are respectively coupled to a first and a second base of the transistors in the second differential amplifier;
each collectors of the transistors in the first differential amplifier receives input voltage signal;
the mirror-coupled emittors of the second differential amplifier receives a gain control signal from the integrator; and
each collectors of the transistors in the second differential amplifier supplies an output current signal.