High efficiency audio amplifier

• US 7,733,178 B1
• Filed: 10/23/2008
• Issued: 06/08/2010
• Est. Priority Date: 10/24/2007
• Status: Active Grant

• Current Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Delano, Cary L., North, Brian B.
• Primary Examiner(s): Choe; Henry K
• Application Number:
  US12/257,287
• Time in Patent Office: 593 Days
• Field of Search: 330/251, 330/207.A, 330/297
• US Class Current: 330/251
• CPC Class Codes: H03F 1/0244 Stepped control
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2203/30105 the pull transistor of the asymmetrically driven SEPP amplifier being a driven current mirror
• CPC Class Codes: H03F 2203/30138 the push transistor of the asymmetrically driven SEPP amplifier being a driven current mirror
• CPC Class Codes: H03F 3/21 with semiconductor devices only H03F3/245 takes precedence
• CPC Class Codes: H03F 3/3022 CMOS common source output SEPP amplifiers H03F3/3008 takes precedence

Abstract

According to the invention, an audio amplifier system for use with a single-ended portable power supply that is referenced to ground, such as a small battery, has a single-channel class G amplifier section, a multiple voltage output charge pump subsystem for supplying complementary pairs of power supply voltages at selected ratiometric levels to an amplifier section, a set of switches on the power supply rails and a power-measuring comparator for selecting which complementary pair of power supply voltages is provided to the amplifier section.

Claims

1. An audio amplifier system for use with a single-ended power supply that is referenced to ground, the amplifier system comprising:

a charge pump subsystem coupled to be driven by said single-ended power supply and operative to generate a first complementary power supply voltage pair and a second complementary power supply voltage pair, including first and second power supply voltages that are positive, and third and fourth power supply voltages that are negative, for supplying all said power supply voltages to an amplifier section; and

a class G amplifier section, said class G amplifier section comprising a single channel, said single channel having

first and second power supply terminals coupled for alternately receiving said first and second power supply voltages,

third and fourth power supply terminals coupled for alternately receiving said third and fourth power supply voltages,

first switching means coupled to alternately switch between said first power supply voltage and said third power supply voltage;

second switching means coupled to alternately switch between said second power supply voltage and said fourth power supply voltage;

a first comparator operative to cause said first switching means to switch power upon sensing a power output voltage approaching a positive peak in excess of a first threshold; and

a second comparator operative to cause said second switching means to switch power upon sensing a power output voltage approaching a negative peak in excess of a second threshold.

2. The audio amplifier system according to claim 1 wherein said first and second comparators are coupled to monitor amplifier output signal power for controlling power switching.

3. The audio amplifier system according to claim 1 wherein said comparator is coupled to monitor amplifier input signal power for controlling the switching.

4. The audio amplifier system according to claim 1 wherein said first and second positive power supply voltages are ratiometric and said third and fourth negative power supply voltages are ratiometric.

5. The audio amplifier system according to claim 1 wherein said charge pump subsystem further comprises a first charge pump having a first charge capacitor and a first charge switching network, and a second charge pump having a second charge capacitor and a second charge switching network, the first charge pump having a three state duty cycle and the second charge pump having a two-state duty cycle, wherein dwell time of all states in the duty cycles are substantially equal in duration, the first charge pump being coupled to the second charge pump so that charge the first charge capacitor and the second charge capacitor produce ratiometric voltages of at least two complementary voltage levels relative to ground.

6. An audio amplifier system for use with a single-ended power supply that is referenced to ground, the amplifier system comprising:

a charge pump subsystem coupled to be driven by said single-ended power supply and operative to generate a first complementary power supply voltage pair, a second complementary power supply voltage pair, and a third complementary power supply voltage pair, including first, second and third power supply voltages that are positive, and fourth, fifth and sixth power supply voltages that are negative, for supplying all said power supply voltages to an amplifier section; and

a class G amplifier section, said class G amplifier section comprising a single channel, said single channel having

first, second and third power supply terminals coupled for intermittently receiving said first, second and third power supply voltages,

fourth, fifth and sixth power supply terminals coupled for intermittently receiving said fourth, fifth and sixth power supply voltages,

switching means coupled to switch among said first complementary power supply voltage pair, said second complementary power supply voltage pair and said third complementary power supply voltage pair; and

a comparator operative to cause said switching means to switch power from said charge pump means to said amplifier section among said first complementary power supply voltage pair, said second complementary power supply voltage pair and said third complementary power supply voltage pair.