Method and apparatus for efficient signal amplification

• US 6,252,455 B1
• Filed: 10/07/1999
• Issued: 06/26/2001
• Est. Priority Date: 10/07/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Smith, Joe Martin, English, Gary Parker, Kurby, Christopher Neil
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/414,279
• Time in Patent Office: 628 Days
• Field of Search: 330/10, 330/129, 330/136, 330/140, 330/141
• US Class Current: 330/136
• CPC Class Codes: H03F 1/0222 by using a signal derived from the input signal
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 2200/102 A non-specified detector of a signal envelope being used in an amplifying circuit

Abstract

An amplifier circuit (100) includes a power amplifier (124) that has a modulated power supply input (125). The modulated power supply input (125) is modulated with a signal related to the amplitude of the signal being amplified by the power amplifier (124). The power amplifier (124) is maintained at a substantially constant operating point. The amplifier circuit (100) also includes a feedback path that generates an error signal as a function of the input signal envelope and the output signal envelope. The error signal is integrated and the resulting integrated error signal drives the gain control of a variable gain element (120) in the amplifier chain prior to the power amplifier (124).

Claims

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

detecting an input signal envelope;

detecting an output signal envelope;

generating an error signal as a function of the input signal envelope and the output signal envelope;

modifying an amplitude of the error signal as a function of the input signal envelope;

adjusting an amplitude of the input signal as a function of the error signal;

amplifying the input signal with an amplifier to produce an output signal; and

modulating the amplifier as a function of the input signal envelope.

2. The method of claim 1 wherein generating an error signal includes:

scaling the input signal envelope to create a scaled input signal envelope;

scaling the output signal envelope to create a scaled output signal envelope; and

taking a difference between the scaled input signal envelope and the scaled output signal envelope to create the error signal.

3. The method of claim 2 wherein adjusting the amplitude of the input signal comprises controlling a variable gain element as a function of the error signal.

4. The method of claim 3 wherein modifying the amplitude of the error signal comprises dividing the error signal by the input signal envelope.

5. The method of claim 3 wherein controlling a variable gain element comprises:

integrating the error signal to create an integrated error signal; and

controlling the variable gain element as a function of the integrated error signal.

6. The method of claim 5 wherein the variable gain element is a variable gain amplifier having a control input, and controlling the variable gain element includes driving the control input with an integrator output.

7. The method of claim 1 wherein modulating the amplifier includes:

amplifying the input signal envelope to create an amplified envelope; and

modulating a supply voltage of the amplifier such that the amplifier operates at a substantially constant compression point.

8. The method of claim 7 wherein amplifying the input signal envelope comprises amplifying the input signal envelope with a pulsewidth modulating amplifier.

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

detecting an input signal envelope;

detecting an output signal envelope;

amplitude limiting the input signal to produce an amplitude limited signal;

amplifying the amplitude limited signal using an amplifier to produce an output signal;

modulating the amplifier with the input signal envelope;

further modulating the amplifier as a function of the output signal envelope;

wherein modulating the amplifier comprises amplifying the input signal envelope to produce an amplified envelope signal by modulating a power supply input of the amplifier with the amplified envelope and modulating a power supply input of the amplifier with the amplified envelope signal; and

wherein further modulating comprises scaling the input signal envelope to produce a scaled input signal envelope;

scaling the output signal envelope to produce a scaled output signal envelope;

taking a difference between the scaled input signal envelope and the scaled output signal envelope to produce an error signal;

summing the error signal with the amplified envelope signal to produce a modulating signal; and

modulating the amplifier with the modulating signal.

10. The method of claim 9 further comprising:

prior to summing the error signal with the amplified envelope signal, integrating the error signal.

11. The method of claim 9 further comprising:

prior to summing the error signal with the amplified envelope signal, amplifying the error signal.

12. The method of claim 9 wherein summing the error signal with the amplified envelope signal comprises summing a current of the error signal with a current of the amplified envelope signal, such that the modulating signal has a modulated current.

13. An amplifier circuit comprising:

a power amplifier having an input node, an output node, and a modulating input node, the power amplifier configured to produce an output signal on the output node;

a variable gain device having an input node configured to receive an input signal having an input signal envelope, an output node coupled to the input node of the power amplifier, and a control input node responsive to a feedback signal;

a feedback loop configured to produce the feedback signal responsive to the input signal and the output signal, wherein the feedback loop includes a gain compensator configured to increase a loop gain of the feedback loop as the input signal envelope decreases in amplitude; and

an envelope amplifier responsive to the input signal envelope, the envelope amplifier configured to drive the modulating input node of the power is amplifier.

14. The amplifier circuit of claim 13 wherein the feedback loop includes:

a first envelope detector coupled to an input node of the amplifier circuit, the first envelope detector configured to produce the input signal envelope;

a second envelope detector coupled to an output node of the amplifier circuit, the second envelope detector configured to produce an output signal envelope; and

a differencing circuit configured to take the difference between the input signal envelope and the output signal envelope, and produce an error signal, the feedback signal being a function of the error signal.

15. The amplifier circuit of claim 14 wherein the gain compensator is configured to divide the error signal by the input signal envelope.

16. The amplifier circuit of claim 14 further comprising an integrator coupled between the differencing circuit and the variable gain device, the integrator being configured to integrate the error signal and produce the feedback signal.

17. The amplifier circuit of claim 13 wherein the envelope amplifier is a pulsewidth modulating amplifier.

18. An amplifier circuit comprising:

a power amplifier configured to produce an output signal having an output signal envelope, the power amplifier having a modulating input responsive to an input signal envelope, and having a signal input responsive to a modulated input signal;

a variable gain element configured to produce the modulated input signal responsive to an input signal and a feedback signal;

a feedback loop configured to produce the feedback signal responsive to the input signal envelope and output signal envelope, wherein a loop gain is modified as a function of the input signal envelope;

wherein the feedback loop comprises a first envelope detector configured to detect the input signal envelope, a second envelope detector configured to produce the output signal envelope; and

a differencing circuit configured to take the difference between the input signal envelope and the output signal envelope, and produce an error signal, the feedback signal being a function of the error signal.

19. The amplifier circuit of claim 18 wherein the feedback loop further includes a gain compensator configured to increase a loop gain of the feedback loop as the input signal envelope decreases in amplitude.

20. The amplifier circuit of claim 19 wherein the gain compensator is configured to divide the error signal by the input signal envelope.

21. The amplifier circuit of claim 18 further comprising an integrator coupled between the differencing circuit and the variable gain element, the integrator being configured to integrate the error signal and produce the feedback signal.

22. An amplifier circuit comprising:

a power amplifier configured to produce an output signal having an output signal envelope, the power amplifier having a modulating input responsive to an input signal envelope, and having a signal input responsive to a modulated input signal;

a variable gain element configured to produce the modulated input signal responsive to an input signal and a feedback signal;

a feedback loop configured to produce the feedback signal responsive to the input signal envelope and output signal envelope, wherein a loop gain is modified as a function of the input signal envelope; and

a pulse width modulating amplifier having an output coupled to the modulating input of the power amplifier.

23. An amplifier circuit comprising:

a power amplifier configured to produce an output signal having an output signal envelope, the power amplifier having a modulating input responsive to an input signal envelope, and to a feedback signal;

a feedback loop configured to produce the feedback signal responsive to the input signal envelope and output signal envelope;

a first envelope detector configured to detect the input signal envelope;

a second envelope detector configured to produce the output signal envelope;

a differencing circuit configured to take the difference between the input signal envelope and the output signal envelope, and produce an error signal, the feedback signal being a function of the error signal;

an envelope amplifier responsive to the input signal envelope, the envelope amplifier configured to produce a first current at the modulating input of the power amplifier; and

an error signal amplifier responsive to the error signal, the error signal amplifier configured to produce a second current at the modulating input of the power amplifier, such that the sum of the first current and the second current modulate the power amplifier.