Digital class-D audio amplifier

• US 6,498,531 B1
• Filed: 08/14/2000
• Issued: 12/24/2002
• Est. Priority Date: 08/14/2000
• Status: Expired due to Term

• Current Assignee: Spectron Corporation
• Original Assignee: Spectron Corporation
• Inventors: Ulrick, John W., Simoni, Wayne P.
• Primary Examiner(s): Shingleton, Michael B
• Application Number:
  US09/638,465
• Time in Patent Office: 862 Days
• Field of Search: 330/10, 330/207.A, 330/251
• US Class Current: 330/10
• CPC Class Codes: H02M 7/53803 with automatic control of output voltage or current
• CPC Class Codes: H03F 1/304 and using digital means
• CPC Class Codes: H03F 1/523 for amplifiers using field-effect devices H03F1/526 takes precedence
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/351 Pulse width modulation being used in an amplifying circuit
• CPC Class Codes: H03F 2200/78 A comparator being used in a controlling circuit of an amplifier
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/2175 using analogue-digital or digital-analogue conversion H03F3/2173 takes precedence

Abstract

A Class-D audio amplifier is disclosed which accepts a digitized audio signal input and drives a load such as a loudspeaker without digital-to-analog conversion. The amplifier preferably comprises (1) means for processing a plurality of digital audio input values to create a plurality of deviation values respectively based on the deviation of the input value'"'"'s relationship from a previous audio input value, (2) means for producing a carrier signal, (3) modulation means for using the deviation values to responsively modulate the carrier signal by varying the frequency of its waveform inversely with the magnitudes of the deviation values, and (4) filter means operative on the modulated carrier to produce an analog voltage capable of driving the load.

Claims

1. An audio amplifier which accepts a plurality of digital audio input values and drives a load such as a loudspeaker without a digital-to-analog converter comprising:

means for processing the plurality of digital audio input value to create a plurality of deviation values respectively based on the deviation of the input value'"'"'s relationship from a previous audio input value;

means for producing a carrier signal;

modulation means for using the deviation values to responsively modulate the carrier signal by varying the frequency of its waveform inversely with the magnitudes of the deviation values; and

filter means operative on the modulated carrier to produce an analog voltage capable of driving the load.

2. An audio amplifier which accepts a digitized audio signal and drives a load such as a loudspeaker without a digital-to-analog converter comprising:

means for receiving a digitized audio signal in the form of a plurality of digital audio input values;

first electrical circuit means for generating an electrical pulse waveform;

digital circuit means for pulse-width modulating the pulses of said waveform in accordance with the digitized audio signal to generally preserve the audio information in the modulated waveform, said digital circuit means varying the frequency of said waveform inversely with the magnitudes of said input values; and

demodulation means operative on the modulated waveform to produce an analog representation of the digitized audio signal.

3. An audio amplifier which accepts a digitized audio signal and drives a load such as a loudspeaker without a digital-to-analog converter comprising:

(a) means for receiving a digitized audio signal in the form of a plurality of digital audio input values;

(b) first electrical circuit means for generating an electrical pulse waveform and including

an accumulator for storing an accumulated digital sum,

a clock for producing a succession of timing pulses,

first means, responsive to the timing pulses when operable, for repeatedly adding a digital value to the accumulated digital sum until the accumulated digital sum reaches an upper trip value,

second means, responsive to the timing pulses when operable, for repeatedly subtracting a digital value from the accumulated digital sum until the accumulated sun reaches the lower trip value, and

means responsive to the accumulated sum reaching the upper trip value to render said second means operable and to render said first means inoperable, and responsive to the accumulated sum reaching the lower trip value to render said first means operable and said second means inoperable;

(c) digital circuit means for pulse-width modulating the pulses of said waveform in accordance with the digitized audio signal to generally preserve the audio information in the modulated waveform, and

(d) demodulation means operative on the modulated waveform to produce an analog representation of the digitized audio signal.

4. The amplifier of claim 3 including bistable circuit means for generating a cyclical electrical waveform having a upper value when said first means is operable and a lower value when said second means is operable.

5. The amplifier of claim 4 including third means responsive to the clock pulse for adding positive or negative values to the accumulator respectively representative of the digital audio input values to vary the time duration in which the waveform is at the first and second values in each cycle.

6. The amplifier of claim 5 including

power supply means to establish upper and lower rail voltages, said upper and lower values of said waveform being respectively generally proportional thereto, and

means responsive to the magnitude of the rail voltages to adjust the digital values applied to the accumulated digital sum by the operable one of the first and second means so that the number of clock pulses per cycle of waveform remain substantially constant with varying rail voltages.

7. The amplifier of claim 5 including

power supply means to establish upper and lower rail voltages, said upper and lower values of said waveform being respectively generally proportionally thereto, and

means responsive to the magnitude of the rail voltages to vary the upper and lower trip values so that the number of clock pulses per cycle of waveform remain substantially constant with varying rail voltages.

8. The amplifier of claim 5 wherein the demodulation means includes means responsive to the duty cycle variations in the waveform to produce a correspondingly varying analog signal level to drive a load such as a loudspeaker.

9. The amplifier of claim 3 including third means responsive to the clock pulse for adding positive or negative values to the accumulator respectively representative of the digital audio input values to vary the time taken by the accumulator to reach the approaching trip level.

10. An audio amplifier which accepts a plurality of digital audio input values and drives a load such as a loudspeaker without a digital-to-analog converter comprising:

accumulator means for storing a count that cyclically increases to an upper trip level and then decreases to a lower trip level;

comparator means responsive to the accumulator for producing a first output while the accumulator is increasing towards the upper trip level and a second output while the accumulator is decreasing towards the lower trip level; and

adder means responsive to the input audio values to add representative values thereof to the accumulated count in order to correspondingly modulate the time duration of the comparator output states counting up and down between upper and lower trip levels.

11. A digital modulator which accepts a plurality of digital audio input values and produces a modulated signal representative thereof without digital-analog conversion comprising:

(a) means for generating a substantially square wave waveform including

(1) an accumulator for storing a digital value;

(2) means for cyclically incrementing the stored value upward and then downward between upper and lower trip values;

(3) means for producing an electrical wave form having a first pulse level while the stored value is incremented upward, and having a second pulse value while the stored value is being incremented downward; and

(b) pulse-width modulating means including

(1) an adder,

(2) register means,

(3) means for sampling the digital audio input values, and

(4) means for adding to the accumulator positive and negative digital values representative of the sampled audio input values to vary the time taken by the accumulator to reaching the approaching trip value, thereby pulse-width modulating the waveform in accordance with the incoming audio values.

12. The modulator of claim 11 including

register means;

means for clocking the sampled input values into the register, said adding means being electrically coupled to the register means to receive the digital input values;

means coupling the output of the adding means to the accumulator; and

feedback means coupled to the adding means to enable the addressing means to produce an output digital value representative of the difference between the sampled input value and the output of the amplifier.