Title: Control circuit for a matrixed four channel audio reproducing system

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1. In an audio reproducing system having a plurality of speakers driven by signals from four channels, which signals are derived from a two channel input, a control circuit comprising:

a. logic circuitry for separating the four channels into two pairs of channels and determining which signals in the two pairs of channels are dominant and providing output signals indicative thereof;

b. adjustable enhancement circuitry connected to receive the output signals from said logic circuitry and providing a pair of output signals for substantially increasing the output of the speakers driven by the dominant channels and reducing the output of the remaining speakers, said enhancement circuitry including first and second amplifier sections connected together so that the output voltage of one section increases as the output voltages of the other section decreases and vice versa, the output voltage of said sections being controlled by the output signals from said logic circuitry, said amplifier sections being constructed so that the output voltage of either section can only decrease to a minimum predetermined value, and said amplifier sections further being constructed so that the decrease of output voltage in either section occurs substantially more rapidly than the increase of output voltage in the other section;

c. four gain control amplifiers each connected to a different channel and connected to drive a speaker associated with that channel, said gain control amplifiers further being connected in pairs and each pair being connected to receive one of the output signals from said adjustable enhancement circuitry for substantially increasing the drive provided by one pair of amplifiers while reducing the drive provided by the remaining pair of amplifiers in accordance with the output signals of said enhancement circuitry; and

d. balance and volume control circuitry connected to said gain control amplifiers for controlling the drive to each of said amplifiers relative to each of the other amplifiers.

2. In an audio reproducing system, a control circuit as claimed in claim 1 wherein said enhancement circuitry includes an enhancement control circuit connected to variably control said amplifier sections and including a pair of transistors connected as a differential amplifier with common emitters and a third transistor coupling the common emitters to a reference potential, means attached to a control electrode of said third transistor for controlling the amount of enhancement, a control electrode of each of said pair of transistors connected to receive the output signals from said logic circuitry, and a unidirectional current conducting device coupled between each control electrode of said pair of transistors and the control electrode of said third transistor for controlling the current flowing in said pair of transistors in accordance with current flowing in said unidirectional current conducting devices.

3. In an audio reproducing system, a control circuit as claimed in claim 2 wherein said third transistor of the enhancement control circuit has variable means coupled to said control electrode thereof for varying the amount of enhancement.

4. In an audio reproducing system, a control circuit as claimed in claim 3 wherein said enhancement circuitry further includes a split collector transistor of a first conductivity type having two collectors, an emitter and a control electrode, first and second transistors of a second conductivity type each having first, second and control electrodes, and a storage capacitor coupled between a reference potential and one collector of said split collector transistor, said one collector providing the amplifier section output, the other collector being connected to the control electrode of said split collector transistor and to the first electrode of said first transistor, the second electrode of said first transistor being coupled to the common emitters of said pair of transistors, the control electrode of said first transistor being connected to the second electrode of said second transistor, the first electrode of said second transistor being connected to the emitter of said split collector transistor and coupled to a voltage source, the control electrode of said second transistor being connected to a voltage divider circuit coupled between the first electrode of said second transistor and the output of said pair of transistors.

5. In an audio reproducing system, a control circuit as claimed in claim 4 wherein said split collector transistor is a PNP conductivity type and the first and second transistors are each of an NPN conductivity type with the first electrode thereof being a collector and the second electrode thereof being an emitter.

6. In an audio reproducing system having a plurality of speakers driven by signals from four channels, which signals are derived from a two channel input, a control circuit comprising:

a. logic circuitry for separating the four channels into two pairs of channels and determining which signals in the two pairs of channels are dominant and providing output signals indicative thereof;

b. adjustable enhancement circuitry connected to receive the output signals from said logic circuitry and to provide a pair of output signals for substantially increasing the output of the speakers driven by the dominant channels and reducing the output of the remaining speakers;

c. four gain control amplifiers each connected to a different channel and connected to drive a speaker associated with that channel, said gain control amplifiers further being connected in pairs and each pair being connected to receive one of the output signals from said enhancement circuit for substantially increasing the drive provided by one pair of amplifiers while reducing the drive provided by the remaining pair of amplifiers in accordance with the output signals of said enhancement circuitry, each of said gain control amplifiers including a differential amplifier having an input coupled to receive the signal from one of the channels and a pair of outputs coupled to differential to single ended converter, one of the outputs of said enhancement circuit being coupled to said differential amplifier for controlling the amount of signal current applied thereto from said one channel; and

d. balance and volume control circuitry connected to said amplifiers for controlling the amount of current flowing in each of said amplifiers relative to each of the other amplifiers.

7. In an audio reproducing system, a control circuit as claimed in claim 6 wherein the differential amplifier includes a pair of common emitter connected transistors, the collectors of which are the outputs, said emitters being coupled to the balance and volume control circuitry, and a pair of diodes connected in a back-to-back relationship between the control electrodes of said common emitter connected transistors with the junction between said pair of diodes being coupled to a reference potential through a pair of transistors one of which has a control electrode coupled to receive an output signal from said adjustable enhancement circuitry to control the potential at the junction of said pair of diodes.

8. In an audio reproducing system, a control circuit as claimed in claim 6 wherein the converter includes first and second transistors of a first conductivity type and a third transistor of a second conductivity type, each of said transistors having first, second and control electrodes, the second electrode of said first transistor being coupled to one of the outputs of the differential amplifier and the second electrode of said second transistor being resistively coupled to the other output of the differential amplifier and to the second electrode of said first transistor, the first electrode of said first transistor being coupled to the control electrode of said third transistor, the first electrode of said second transistor and the second electrode of said third transistor being coupled to a source of voltage, and the control electrode of said first transistor being coupled to a second source of voltage.

9. In an audio reproducing system, a control circuit as claimed in claim 8 wherein the third transistor is a lateral split collector type and the second collector is connected to the control electrode thereof.

10. In an audio reproducing system having a plurality of speakers driven by signals from four channels, which signals are derived from a two channel input, a control circuit comprising:

a. logic circuitry for separating the four channels into two pairs of channels and determining which signals in the two pairs of channels are dominant and providing output signals indicative thereof;

b. enhancement circuitry connected to receive the output signals from said logic circuitry and to provide a pair of output signals for substantially increasing the output of the speakers driven by the dominant channels and reducing the output of the remaining speakers;

c. four gain control amplifiers each connected to a different channel and connected to drive a speaker associated with that channel, said gain control amplifiers further being connected in pairs and each pair being connected to receive one of the output signals from said adjustable enhancement circuitry for substantially increasing the drive provided by one pair of amplifiers while reducing the drive provided by the remaining pair of amplifiers in accordance with the output signals from said adjustable enhancement circuitry; and

d. balance and volume control circuitry connected to said amplifiers for controlling the amount of current flowing in each of said amplifiers relative to each of the other amplifiers, said balance and volume control circuitry including a balanced differential amplifier circuit conducting the control current for all four of said gain control amplifiers in one leg, said differential amplifier circuit including four separate legs coupled to said one leg and each of said four separate legs conducting the current for a separate one of said gain control amplifiers, and controls coupled to said one leg for controlling the total volume and to said four separate legs for controlling the balance or relative volume between channels.

11. In an audio reproducing system, a control circuit as claimed in claim 10 having means for providing a reference potential and wherein the one leg includes a first transistor having a first electrode coupled to said means for providing reference potential, a second electrode coupled to the emitters of a first pair of common emitter connected transistors, and a control electrode coupled to a total volume control for controlling the amount of current flowing through said first transistor.

12. In an audio reproducing system, a control circuit as claimed in claim 11 wherein one transistor of the first pair of common emitter connected transistors has the emitters of a second pair of common emitter connected transistors coupled to the collector thereof and the other transistor of the first pair has the emitters of a third pair of common emitter connected transistors coupled to the collector thereof.

13. In an audio reproducing system, a control circuit as claimed in claim 11 wherein the control electrodes of the transistors in the first pair are coupled to a first control for unbalancing the currents flowing in each of the transistors in the first pair to control the relative volume between the two pairs of channels.

14. In an audio reproducing system, a control circuit as claimed in claim 12 wherein the control electrodes of the transistors in the second pair are coupled to a second control for unbalancing the currents flowing in each of the transistors in the second pair to control the relative volume between the two channels in one of the pairs of channels and the control electrodes of the transistors in the third pair are coupled to a third control for unbalancing the currents flowing in each of the transistors in the third pair to control the relative volume between the two channels in the other of the pairs of channels.
Other info:

Inventors: Gay, Michael J. (Geneva, CH)

Application Number: 503833
Filing Date: 1974-09-06
Publication_date: 1976-02-10
Assignee: Motorola, Inc. (Chicago, IL)
Primary Class(es): 381/22 381/23
Other Classes:
US Patent Ref:

3451006	Jun, 1969	Angaar, Jr.	330/30.
3473139	Oct, 1969	Legler	330/30.
3725583	Apr, 1973	Gunderson et al.	179/1.
3794781	Feb, 1974	Bauer	179/1.
3798373	Mar, 1974	Bauer	179/100.
3821471	Jun, 1974	Bauer	179/100.
3825684	Jul, 1974	Ito et al.	179/1.

Other Refs:
Primary Examiner: Cooper, William C.
Assistant Examiner: D'Amico, Thomas
Attorney: Weiss; Harry M., Jones, Jr.; Maurice J.