Multi-stage amplifier with multiple sets of fixed and variable voltage rails

• US 20080174372A1
• Filed: 03/30/2007
• Published: 07/24/2008
• Est. Priority Date: 01/19/2007
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Tucker, John C., Prasad, Ammisetti V.
• Granted Patent: US 8,362,838 B2
• Time in Patent Office: Days
• US Class Current: 330/297
• CPC Class Codes: H03F 1/0222 by using a signal derived from the input signal
• 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 2200/405 the output amplifying stage of an amplifier comprising more than three power stages
• CPC Class Codes: H03F 2200/408 the output amplifying stage of an amplifier comprising three power stages
• 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 2200/516 Some amplifier stages of an amplifier use supply voltages of different value
• CPC Class Codes: H03F 2203/45138 Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
• CPC Class Codes: H03F 3/187 in integrated circuits
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit

Abstract

A signal processing system and method utilizes a multi-stage amplifier to amplify an input signal. The multi-stage amplifier uses a mixed set of voltage rails to improve the operating efficiency of at least one of the amplification stages while allowing other amplification stages to operate in a predetermined operating mode. Efficiency of at least one of the stages is improved by supplying at least one variable voltage rail to an amplification stage of the multi-stage amplifier. The variable voltage rail varies in response to changes in an input signal voltage to the amplification stage. Accordingly, at least one amplification stage utilizes a variable voltage rail, and all amplification stages are supplied with a set of voltage rails that provides sufficient input signal headroom, thus, providing amplification stage efficiency and adequate voltage to allow operation of all amplification stages.

Claims

1. A method of amplifying an input signal, the method comprising:

receiving an input signal with a multi-stage amplifier;

receiving a mixed set of voltage rails, wherein each amplification stage of the multi-stage amplifier receives a set of the voltage rails and at least one member of one set of the voltage rails is a variable voltage rail; and

amplifying the input signal using the multi-stage amplifier to generate an amplified input signal.

2. The method of claim 1 wherein the set of voltage rails received by a last stage of the multi-stage amplifier comprises two variable voltage rails.

3. The method of claim 2 wherein the set of voltage rails for each of the stages of the multi-stage amplifier includes one of the variable voltage rails received by the last stage of the multi-stage amplifier and the set of voltage rails received by each of the stages of the multi-stage amplifier except the last stage also includes a fixed voltage rail.

4. The method of claim 1 wherein the input signal comprises an audio signal, the method further comprising:

providing the amplified input signal to at least one speaker.

5. The method of claim 1 further comprising:

for each amplification stage, generating an output signal;

for each amplification stage, except an initial amplification stage, receiving the output signal of a preceding amplification stage; and

receiving the variable voltage rail with one of the amplification stages, wherein the variable voltage rail received by the amplification stage varies in response to the output signal received by the amplification stage to increase efficiency of the amplification stage.

6. The method of claim 1 wherein the mixed set of voltage rails comprises fixed voltage rails and the variable voltage rail.

7. A signal processing device comprising:

a multi-stage amplifier, the amplifier comprising;

a first amplification stage having an output node and first and second power supply nodes, wherein during operation the first and second power supply nodes of the first amplification stage are coupled to respective first and second voltage rails; and

a second amplification stage, coupled to the output node of the first amplification stage, having first and second power supply nodes, wherein during operation the first and second power supply nodes of the second amplification stage are respectively coupled to a variable voltage rail and to a third voltage rail, and the first voltage rail is greater than the variable voltage rail.

8. The signal processing system of claim 7 wherein during operation of the multi-stage amplifier, the second voltage rail is equal to the third voltage rail.

9. The signal processing system of claim 7 wherein, during operation of the multi-stage amplifier, the first voltage rail has a fixed voltage and the second and third voltage rails vary over time.

10. The signal processing system of claim 7 wherein the multi-stage amplifier further comprises:

a third amplification stage, coupled between the first and second amplification stages, having first and second power supply nodes, wherein during operation the first and second power supply nodes of the third amplification stage are coupled respectively to the first and second voltage rails.

11. The signal processing system of claim 7 wherein the multi-stage amplifier further comprises at least one input terminal to receive an audio input signal and at least one output terminal to supply an amplified version of the audio input signal.

12. The signal processing system of claim 7 wherein the multi-stage amplifier further comprises at least one input terminal to receive an audio input signal and at least one output terminal to supply an amplified version of the audio input signal, the system further comprising:

an input source of the audio input signal coupled to the input terminal to supply the audio input signal to the multi-stage amplifier; and

at least one speaker coupled to the output terminal of the multi-stage amplifier.

13. The signal processing system of claim 7 further comprising:

a first power supply coupled to the first power supply node of the first amplification stage; and

a second power supply coupled to the second power supply node of the first amplification stage and to the first and second power supply nodes of the second amplification stage.

14. The signal processing system of claim 7 wherein the multi-stage amplifier comprises integrated circuit components.

15. A method of amplifying an input signal, the method comprising:

receiving first and second power supply voltages with a first amplification stage of a multi-stage amplifier;

receiving third and fourth power supply voltages with a second amplification stage of the multi-stage amplifier, wherein the first power supply voltage is greater than the third power supply voltage, the third power supply voltage varies over time during operation of the multi-stage amplifier and the first and third power supply voltages are more positive than respective second and fourth power supply voltages;

receiving an input signal with the multi-stage amplifier; and

amplifying the input signal using the multi-stage amplifier to generate an amplified input signal.

16. The method of claim 15 wherein the second power supply voltage equals the third power supply voltage.

17. The method of claim 15 wherein the second power supply voltage and the third power supply voltage vary over time during operation of the multi-stage amplifier, and the first power supply voltage is fixed.

18. The method of claim 15 further comprising:

supplying the first and second power supply voltages to a third amplification stage of the multi-stage amplifier, wherein the third amplification stage is an intermediary amplification stage.

19. The method of claim 15 further comprising:

providing the amplified input signal to at least one speaker.

20. A signal processing system comprising:

a first amplification stage, wherein during operation the first amplification stage receives a fixed supply voltage and a first variable supply voltage, and the fixed supply voltage is greater than the first variable supply voltage;

a second amplification stage, coupled to an output of the first amplification stage, wherein during operation the second amplification stage receives the fixed supply voltage and the variable supply voltage; and

a third amplification stage, coupled to an output of the second amplification stage, wherein during operation the third amplification stage receives a second variable supply voltage and the first variable supply voltage, wherein the fixed supply voltage is greater than a maximum second variable supply voltage.

21. The signal processing system of claim 20 further comprising:

an audio input signal generator, coupled to an input of the first amplification stage; and

at least one speaker coupled to an output of the third amplification stage.

22. The signal processing system of claim 21 further comprising:

a first power supply coupled to the first amplification stage to provide the fixed supply voltage; and

a second power supply coupled to the second and third amplification stages to provide the first and second variable supply voltages.

23. The signal processing system of claim 20 wherein the first amplification stage includes differential input nodes.