Amplifier circuit and method of amplifying a signal in an amplifier circuit

• US 9,252,729 B2
• Filed: 02/19/2015
• Issued: 02/02/2016
• Est. Priority Date: 08/03/2007
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic International Semiconductor Ltd. (Cirrus Logic Incorporated)
• Inventors: Lesso, John P.
• Primary Examiner(s): Nguyen, Patricia T
• Application Number:
  US14/626,468
• Publication Number:
  US 20150162885A1
• Time in Patent Office: 348 Days
• Field of Search: 330/279, 330/297, 330/127
• US Class Current: 1/1
• CPC Class Codes: H03F 1/0216 Continuous control
• CPC Class Codes: H03F 1/0227 using supply converters
• CPC Class Codes: H03F 1/0261 with control of the polarisation voltage or current, e.g. gliding Class A
• CPC Class Codes: H03F 1/30 Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in differential amplifiers H03F3/45479
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/504 the supply voltage or current being continuously controlled by a controlling signal, e.g. the controlling signal of a transistor implemented as variable resistor in a supply path for, an IC-block showed amplifier
• CPC Class Codes: H03F 3/185 with field-effect devices H03F3/187 takes precedence
• CPC Class Codes: H03F 3/193 with field-effect devices H03F3/195 takes precedence
• CPC Class Codes: H03G 3/001 Digital control of analog signals
• CPC Class Codes: H03G 3/3015 using diodes or transistors

Abstract

An amplifier circuit, comprising: an input, for receiving an input signal to be amplified; a power amplifier, for amplifying the input signal; a switched power supply, having a switching frequency, for providing at least one supply voltage to the power amplifier; and a dither block, for dithering the switching frequency of the switched power supply. The dither block is controlled based on the input signal. Another aspect of the invention involves using first and second switches, each having different capacitances and resistances, and using the first or second switch depending on the input signal or volume signal. Another aspect of the invention involves controlling a bias signal provided to one or more components in the signal path based on the input signal or volume signal.

Claims

1. An amplifier circuit, comprising:

an input, for receiving an input signal to be amplified;

an amplifier, for amplifying the input signal;

a switched power supply, having a switching frequency, for providing at least one supply voltage to the amplifier; and

a dither block, for dithering the switching frequency of the switched power supply;

wherein the dither block is controlled based on a control signal, wherein the control signal is based on at least one of the input signal and a volume signal for controlling a variable gain applied to the input signal.

2. An amplifier circuit as claimed in claim 1, wherein the dither block is controlled based on the control signal such that the dither block operates in a first mode when the control signal has a first amplitude, and such that the dither block operates in a second mode when the control signal has a second amplitude.

3. An amplifier circuit as claimed in claim 2, wherein the first mode comprises the dither block dithering the switching frequency by a first amount, and wherein the second mode comprises the dither block dithering the switching frequency by a second amount, the first amount being greater than the second amount.

4. An amplifier circuit as claimed in claim 2, wherein the first mode comprises the dither block dithering the switching frequency at a first frequency, and wherein the second mode comprises the dither block dithering the switching frequency at a second frequency, the first frequency being greater than the second frequency.

5. An amplifier circuit as claimed in claim 2, wherein the first mode comprises the dither block dithering the switching frequency, and wherein the second mode comprises the dither block not dithering the switching frequency.

6. An amplifier circuit as claimed in claim 2, wherein the first amplitude of the control signal is greater than the second amplitude of the control signal.

7. An amplifier circuit as claimed in claim 1, further comprising:

an envelope detector for detecting the envelope of the input signal and for outputting the control signal in accordance with the detected input signal envelope.

8. An amplifier circuit as claimed in claim 1, further comprising a preamplifier, for receiving the input signal and outputting a pre-amplified signal in accordance with the volume signal.

9. An amplifier circuit as claimed in claim 1, wherein the control signal is based on the input signal.

10. An amplifier circuit as claimed in claim 1, wherein the control signal is based on the volume signal.

11. An amplifier circuit as claimed in claim 1, wherein the control signal is based on both the input signal and the volume signal.

12. An amplifier circuit as claimed in claim 11, wherein the input signal is multiplied by the volume signal to generate the control signal.

13. An amplifier circuit as claimed in claim 1, wherein the switched power supply is a level-shifting charge pump.

14. An amplifier circuit as claimed in claim 13, wherein said level shifting charge pump supplies a plurality of supply voltages to the amplifier, said level shifting charge pump comprising:

an input terminal and a common terminal for connection to an input voltage;

first and second output terminals for outputting said plurality of supply voltages, said output terminals in use being connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors;

first and second flying capacitor terminals for connection to a flying capacitor;

a network of switches that is operable in a plurality of different states for interconnecting said terminals; and

a controller for operating said switches in a sequence of said states, said sequence being adapted repeatedly to transfer packets of charge from said input terminal to said reservoir capacitors via said flying capacitor depending on the state, thereby generating positive and negative supply voltages together spanning a voltage approximately equal to the input voltage, and centered on the voltage at the common terminal.

15. An amplifier circuit as claimed in claim 1, wherein the switched power supply is a dual-mode charge pump.

16. An amplifier circuit as claimed in claim 15, wherein said dual-mode charge pump supplies a plurality of supply voltages to the amplifier, said dual-mode charge pump comprising:

an input terminal and a common terminal for connection to an input voltage;

first and second output terminals for outputting said plurality of supply voltages, said first and second output terminals being, in use, connected to said common terminal via respective first and second loads and also via respective first and second reservoir capacitors;

first and second flying capacitor terminals for connection to one flying capacitor;

a network of switches that is operable in a plurality of different states for interconnecting said terminals; and

a controller for operating said network of switches in a sequence of said different states,

wherein said controller is operable in first and second modes, and where, in the first of said modes, said sequence is adapted repeatedly to transfer packets of charge from said input terminal to said reservoir capacitors via said flying capacitor depending on the state, thereby generating positive and negative supply voltages together spanning a voltage approximately equal to the input voltage, and centered on the voltage at the common terminal.

17. An audio system, comprising an amplifier circuit as claimed in claim 1, wherein the audio system is at least one of:

a portable device;

a mains-powered device;

an in-car, in-train, or in-plane entertainment system;

a noise-cancellation system.

18. A method of amplifying a signal in an amplifier circuit, said amplifier circuit comprising an amplifier and a switched power supply, said method comprising:

receiving an input signal;

providing at least one supply voltage from the switched power supply to the amplifier, said step of providing comprising;

switching the switched power supply at a switching frequency; and

on the basis of a control signal, dithering the switching frequency; and

amplifying the input signal in the amplifier;

wherein the control signal is based on at least one of the input signal and a volume signal for controlling a variable gain applied to the input signal.

19. A method as claimed in claim 18, further comprising:

wherein the control signal is based on both the input signal and the volume signal.

20. An amplifier circuit comprising:

a switched power supply for supplying at least one supply voltage to an amplifier; and

a controller operable to dither a switching frequency of the switched power supply;

wherein the dither of the switching frequency varies based on an indication of amplitude of a signal being amplified by the amplifier.