Method and system for digitally controlling a multi-channel audio amplifier

• US 20040176955A1
• Filed: 12/22/2003
• Published: 09/09/2004
• Est. Priority Date: 12/20/2002
• Status: Active Grant

• Current Assignee: Core Brands, LLC (Melrose Industries Plc)
• Original Assignee: AVC Group, LLC. (Melrose Industries Plc)
• Inventors: Farinelli, Robert P. Jr., Dunaway, Jason
• Granted Patent: US 8,005,230 B2
• Time in Patent Office: Days
• US Class Current: 704/255
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H03F 2200/321 Use of a microprocessor in an amplifier circuit or its control circuit
• CPC Class Codes: H03F 2200/462 the current being sensed
• CPC Class Codes: H03F 2200/471 the voltage being sensed
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H03G 11/04 Limiting level dependent on strength of signal; Limiting level dependent on strength of carrier on which signal is modulated H03G11/008 takes precedence
• CPC Class Codes: H03G 3/301 the gain being continuously variable

Abstract

Audio signals are processed in a manner that facilitates control for overpower conditions. According to an example embodiment of the present invention, an audio processing circuit is configured and arranged for controlling an output audio signal as a function of an output power and/or clip condition. The audio processing circuit is adapted to approximate output power from an amplifier independent from output load and varying line conditions. When an overpower and/or clip condition is approximated, a signal is generated to reduce the output power by, e.g., reducing the-signal gain and/or disconnecting the output.

Claims

1. An audio processing system comprising:

means, responsive to an audio input signal, for generating an amplified audio output signal;

means, responsive to the amplified audio output signal, for generating an over power detection signal indicating an overpower condition independent of an output load; and

means, responsive to the over power detection signal, for adjusting the digitally controlled input gain.

2. An audio processing system of claim 1, further including:

means, responsive to the amplified audio output signal, for generating a clip detection signal indicating a clip detection condition dependent on the amplifier'"'"'s power supply rail voltage; and

means, responsive the clip detection signal, for adjusting the digitally controlled input gain to eliminate the clip condition.

3. An audio processing system comprising:

a digital input gain circuit having at least one input gain block, wherein each input gain block generates an output signal in response to an audio input signal and a digital gain control signal;

a power amplifier circuit, coupled to an output load, having at least one power amplifier, wherein each power amplifier generates an audio output signal in response to an input signal;

an overpower detection circuit for generating an overpower detection signal in response to each audio output signal, wherein each overpower detection signal is adapted to be generated independent of varying output load and line conditions associated with the power amplifier circuit;

a microprocessor and a keypad coupled to the microprocessor for selecting an audio output signal and entering input gain levels for a selected audio output signal; and

the microprocessor for generating digital gain control signals in response to at least one overpower detection signal and input gain levels.

4. The audio processing system of claim 3, wherein the system further includes a clip detection circuit for generating a clip detection signal in response to each audio output signal, the microprocessor being adapted for generating digital gain control signals in response to at least one clip detection signal and the input gain levels.

5. The audio processing system of claim 3, wherein the system further includes a switching means for coupling an input source to at least one audio output signal.

6. The audio processing system of claim 3, wherein the system further includes a an output disconnect block for removing each power amplifier from being coupling with its output load.

7. The audio processing system of claim 3, wherein the system further includes a display screen for indicating an active audio output signal, a clip detection signal, a mute audio output signal, a gain level, and fault status information for all audio output signals.

8. The audio processing system of claim 3, wherein the system further includes a clip detection circuit for generating a clip detection signal in response to each audio output signal, the microprocessor being adapted for generating digital gain control signals in response to at least one clip detection signal and the input gain levels;

wherein each power amplifier has a built-in fault detection circuit that is adapted to monitor at least one of;

power failure;

overheating;

short circuit; and

improper rail voltage.

9. The audio processing system of claim 3, wherein the keypad and the microprocessor are adapted to allow a user to lock gain levels, unlock gain levels, enable the clip detection circuit, and disable the clip detection circuit.

10. The audio processing system of claim 3, wherein the digital input gain circuit operates as a digital potentiometer having programmable gain settings.

11. The audio processing system of claim 10, wherein the digital input gain circuit operating as a digital potentiometer has preset variable gain settings dependent on preset variable resistance settings.

12. The audio processing system of claim 3, wherein the microprocessor generates digital gain control signals in response to input gain levels and mute signals received from a keypad, at least one clip detection signal, and at least one overpower detection signal.

13. The audio processing system of claim 3, wherein the microprocessor selects an audio channel, sets a gain level for the channel, enables a clip detection circuit for the channel, disables a clip detection circuit for the channel and locks out further adjustments to the gain level of the channel.

14. The audio processing system of claim 3, wherein the microprocessor removes each power amplifier from its output load when a fault detection signal is present by engaging its output disconnect relay and sends fault detection signals to a display screen if a fault condition is received from a fault detection circuit of a power amplifier.

15. The audio processing system of claim 3, wherein the clip detection circuit with an analog detection integrates a clip signal, thereby ignoring amplifier clipping events lasting less than a predetermined attack time.

16. The audio processing system of claim 3, wherein the clip detection circuit with an analog detection integrates a non-clip signal;

thus ignoring amplifier non-clipping events lasting less than a predetermined release time.

17. The audio processing system of claim 3, wherein the clip detection circuit with the analog detection that looks at the full audio spectrum for a potential clip signal, and not just in the low frequency band.

18. The audio processing system of claim 3, wherein the clip detection circuit derives its clip threshold level from a scaled positive audio amplifier voltage rail thereby facilitating automatic tracking of fluctuations in rail voltages due to varying load and varying line conditions.

19. The audio processing system of claim 3, wherein the microprocessor sends digital control gain signals, having digitally set time constants, to the digital input gain circuit.

20. The audio processing system of claim 3, wherein the system further includes a clip detection circuit for generating a clip detection signal in response to each audio output signal, the microprocessor being adapted for generating digital gain control signals in response to at least one of:

a clip detection signal, an overpower detection signal and the input gain levels, the microprocessor further being programmed to;

in response to at least one of an overpower or clip condition indicated by an overpower or clip signal, enter an attack mode in which, after a preset attack time, the digital gain control signal is rapidly reduced to a reduced level; and

in response to the at least one of an overpower or clip condition ceasing to be indicated by an overpower or clip signal after the digital gain control signal has been reduced, enter a release mode in which the digital gain control signal is maintained at the reduced level for a set release time and, at the end of the set release time, in which the digital gain control is returned to the input gain levels.

21. The audio processing system of claim 20, wherein the microprocessor is programmed to:

in response to the at least one of an overpower or clip condition existing and the preset attack time not being met, increment an attack time counter;

in response to the overpower or clip condition persisting, repeat the step of incrementing the attack time counter until the attack time has been met and, when the attack time has been met, reduce the digital gain control signal and reset the attack time;

in response to the at least one of an overpower or clip condition ceasing to be indicated by an overpower or clip signal and the release time not being met, incrementing a release time counter; and

in response to the overpower or clip condition continuing to cease to be indicated after the digital gain control signal has been reduced, repeat the step of incrementing the release time counter until the release time has been met and, when the release time has been met, returning the digital gain control to the input gain levels.