Digitally controlled audio amplifier with voltage limiting

• US 5,255,324 A
• Filed: 12/26/1990
• Issued: 10/19/1993
• Est. Priority Date: 12/26/1990
• Status: Expired due to Fees

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Brewer, James E., Abowd, Peter S., Raffaeli, Frank W.
• Primary Examiner(s): Dwyer, James L.
• Assistant Examiner(s): Chiang, Jack
• Application Number:
  US07/633,919
• Time in Patent Office: 1,028 Days
• Field of Search: 381/98, 381/101, 381/102, 381/104, 381/106, 381/107, 381/108, 381/55, 381/86, 330/127, 330/129, 330/138, 330/279, 330/280
• US Class Current: 381/107
• CPC Class Codes: H03G 11/00 Limiting amplitude; Limiting rate of change of amplitude ; Clipping in general
• CPC Class Codes: H03G 9/005 of digital or coded signals
• CPC Class Codes: H03G 9/02 in untuned amplifiers

Abstract

An audio system employs a microcontroller to supervise the operation of an audio system including a digitally controlled audio processor which controls at least a wideband and a narrowband gain for the audio signal. The narrowband gain may preferably comprise a bass boost to the audio signal. Clipping distortion of the audio signal is avoided by sensing clipping in a power amplifier and reducing the digital commands for the wideband gain and the narrowband gain according to a method which reduces narrowband gain in preference to the wideband gain. After the narrowband gain is reduced to a predetermined gain, the wideband gain may be reduced if clipping persists. When clipping ceases, the narrowband gain is likewise restored to its original gain in preference to restoring of the wideband gain.

Claims

1. An audio system comprising:

microcontroller means for controlling operation of said audio system by generating digital commands in response to sensed inputs;

digitally-controlled audio processor means coupled to said microcontroller means for controlling a narrowband audio gain and a wideband audio gain of audio signals in response to said digital commands from said microcontroller means;

wherein said digital commands comprise a wideband command signal and a narrowband command signal;

power amplifier means coupled to said audio processor means for amplifying said audio signal;

clip detect means coupled to said audio amplifier means for generating a clip signal indicative of the occurrence of clipping in said power amplifier means; and

interface means coupling said clip detect means with said microcontroller means for integrating said clip signal and for transmitting a digital limit signal to said microcontroller means when said integration indicates that clipping distortion exceeds a threshold;

said microcontroller means sensing said limit signal and altering said narrowband digital command to gradually reduce said narrowband gain while said limit signal is present until a predetermined narrowband gain is reached and altering said wideband command signal while simultaneously maintaining said narrowband command signal to gradually reduce said wideband gain if said limit signal persists.

2. The system of claim 1 wherein said microcontroller means further gradually alters said digital commands after the cessation of said limit signal to restore said narrowband gain to its original, non-altered value prior to restoring said wideband gain.

3. The system of claim 1 wherein said narrowband gain and said wideband gain are altered in step changes of gain, each step change reduction in gain following a respective time delay corresponding to a predetermined attack time.

4. The system of claim 2 wherein said narrowband gain and said wideband gain are altered in step changes of gain, each step change reduction in gain following a respective time delay corresponding to a predetermined attack time and each step change restoration in gain following a respective time delay corresponding to a predetermined release time.

5. The system of claim 1 wherein said threshold is about 10 percent harmonic distortion.

6. The system of claim 1 wherein said narrowband gain is a bass gain.

7. The system of claim 1 wherein said microcontroller means senses said limit signal at Predetermined intervals.

8. The system of claim 1 wherein said limit signal provides an interrupt for said microcontroller means.

9. A method for limiting clipping distortion in an audio system having a microcontroller for digitally controlling a bass gain and a wideband volume gain in an audio processor in steps according to bass and volume digital commands based on operator input settings for bass and volume, said method comprising the steps of:

detecting the occurrence of clipping in said audio system;

generating a limit signal when clipping . distortion exceeds a threshold; and

recurrently executing the steps of;

checking for the occurrence of said limit signal;

if said limit signal is present then checking whether said bass digital command is above a predetermined reference command level and if so then waiting for a first predetermined delay and then reducing said bass digital command by at least one step, but if said bass digital command is not above said predetermined reference command level then waiting for a second predetermined delay and then reducing said volume digital command by at least one step; and

if said limit signal is not present then checking whether said bass digital command corresponds to said bass input setting and if not then waiting for a third predetermined delay and then increasing said bass digital command by at least one step, but if said bass digital command corresponds to said bass input setting then checking whether said volume digital command corresponds to said volume input setting and if not then waiting for a fourth predetermined delay and then increasing said volume digital command by at least one step.

10. A method for limiting clipping distortion in an audio system having a microcontroller for digitally controlling a bass gain and a wideband volume gain in an audio processor in steps according to bass and volume digital commands based on operator input settings for bass and volume, said method comprising the steps of:

detecting the occurrence of clipping in said audio system;

generating a limit signal when clipping distortion exceeds a threshold; and

gradually reducing said bass digital command in response to said limit signal and then gradually reducing said volume digital command if said bass digital command has been reduced to a predetermined value, and said limit signal persists, and simultaneous to reduce said volume digital command, while maintaining said bass digital command.

11. The method of claim 10 further comprising the steps of:

increasing said bass digital command if said bass digital command does not correspond to said bass input setting and said limit signal is not present; and

increasing said volume digital command if said volume digital command does not correspond to said volume input setting, said bass digital command does correspond to said bass input setting, and said limit signal is not present.

12. The method of claim 10 wherein said limit signal causes an interrupt in said microcontroller.