Load envelope following amplifier system

• US 6,349,216 B1
• Filed: 07/22/1999
• Issued: 02/19/2002
• Est. Priority Date: 07/22/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Alberth, William P. Jr., Klomsdorf, Armin, Winkelmann, Luke
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): Milord, Marceau
• Application Number:
  US09/359,586
• Time in Patent Office: 943 Days
• Field of Search: 455/104, 455/107, 455/571, 455/108, 455/572, 455/115, 455/116, 455/550, 455/127, 455/126, 375/297, 375/296
• US Class Current: 455/550.1
• CPC Class Codes: H03F 1/0222 by using a signal derived from the input signal
• CPC Class Codes: H03F 1/0261 with control of the polarisation voltage or current, e.g. gliding Class A
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2200/207 A hybrid coupler being used as power measuring circuit at the output of an amplifier circuit
• CPC Class Codes: H03F 2200/387 A circuit being added at the output of an amplifier to adapt the output impedance of the amplifier
• CPC Class Codes: H04B 1/0458 Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages matching circuits in general H03H

Abstract

A load envelope following (LEF) amplifier system to increase the efficiency of amplification systems that employ linear modulation schemes. The LEF system has a signal amplifier for receiving an input signal that has an amplitude modulation (AM) envelope. The signal amplifier produces an amplified version of the input signal. A variable impedance network is coupled to an output of the signal amplifier and substantially continuously presents various impedances to the output of the signal amplifier in response to a load control signal. An envelope mapping circuit is coupled to the variable impedance network to produce the load control signal in response to and indicative of the substantially continuously varying amplitude of the AM envelope of the input signal.

Claims

1. A radio frequency transmitter for transmitting a modulated information signal, the radio frequency transmitter comprising:

a control circuit for converting user input information into an input signal and for providing an indication of a desired average transmit power;

transmitter circuitry coupled to the control circuit for processing the input signal to form a modulated input signal having an amplitude modulation (AM) envelope; and

a load envelope following power amplifier (LEF PA) system coupled to the transmitter circuitry, the LFP PA system including,

a power amplifier coupled to receive the modulated input signal to produce an amplified signal at an output of the power amplifier,

a variable impedance network coupled to receive the amplified signal and a load control signal, the load control signal causing the variable impedance network to continuously present various impedances to the output of the power amplifier,

an envelope mapping and control circuit coupled to the variable impedance network, the control circuit, and the transmitter circuitry, the envelope mapping and control circuit coupled to receive the indication of the desired average transmit power and to produce the load control signal responsive to both amplitude variations of the AM envelope and the desired average transmit power, the envelope mapping and control circuit to produce a supply voltage control signal in response to the indication of the desired average transmit power, and

a voltage control circuit for receiving the supply voltage control signal, producing a supply voltage responsive to the supply voltage control signal, and applying the supply voltage to the power amplifier.

2. A radio frequency transmitter for transmitting a modulated information signal, the radio frequency transmitter comprising:

a control circuit for converting user input information into an input signal and for providing an indication of a desired average transmit power;

transmitter circuitry coupled to the control circuit for processing the input signal to form a modulated input signal having an amplitude modulation (AM) envelope; and

a load envelope following power amplifier (LEF PA) system coupled to the transmitter circuitry, the LEF PA system including,

a power amplifier coupled to receive the modulated input signal to produce an amplified signal at an output of the power amplifier,

a variable impedance network coupled to receive the amplified signal and a load control signal, the load control signal causing the variable impedance network to continuously present various impedances to the output of the power amplifier, and

an envelope mapping and control circuit coupled to the variable impedance network, the control circuit, and the transmitter circuitry, the envelope mapping and control circuit coupled to receive the indication of the desired average transmit power to produce the load control signal responsive to both amplitude variations of the AM envelope and the desired average transmit power, the envelope mapping and control circuit to produce a bias control voltage directly proportional to the indication of the desired average transmit power,

wherein the bias control voltage is applied to the power amplifier to cause a bias current of the power amplifier to vary in response to the indication of the desired average transmit power.

3. A load envelope following amplifier system, comprising:

a signal amplifier having an input for receiving an input signal having a amplitude modulation (AM) envelope, the amplifier for producing an amplified version of the input signal at an output;

a variable impedance network coupled to the output of the signal amplifier, the variable impedance network for presenting different impedances to the output of the signal amplifier responsive to a load control signal; and

an envelope mapping circuit coupled to the variable impedance network and generating the load control signal as a function of at least the amplitude modulation envelope, only a portion of the AM envelope being used by the envelope mapping circuit for producing the load control signal.

4. The load envelope following amplifier system according to claim 3, wherein the portion of the AM envelope is the top portion of the envelope.

5. The load envelope following amplifier system according to claim 4, wherein the top portion is the top 8 dB of the envelope.

6. The load envelope following amplifier system according to claim 3, wherein the variable impedance network includes a variable capacitance.

7. The load envelope following amplifier system according to claim 3, further including:

transmitting circuitry coupled to the input of the signal amplifier; and

distortion control circuitry coupled to the envelope mapping circuit and the transmit circuitry, wherein the distortion control circuitry causes the transmit circuitry to impress distortion upon the input signal before the input signal is input to the signal amplifier.

8. The load envelope following amplifier system according to claim 3, further including a signal quality detector coupled to the impedance network and monitoring the peak to average ratio of the amplified version of the input signal, the envelope mapping circuit generating the load control signal to cause the amplified version of the input signal to have a substantially constant peak to average ratio.

9. The load envelope following amplifier system according to claim 3, further including a signal quality detector coupled to the impedance network and monitoring adjacent channel power, the envelope detector generating the load control signal to cause the signal amplifier and impedance network to produce less than a predetermined level of adjacent channel power.

10. A method of operating a radiotelephone multimode radio frequency transmitter including a signal amplifier, an impedance network, and an envelope mapping circuit comprising the steps of:

receiving an input signal having an amplitude modulation envelope;

receiving a mode input indicating the operating mode of the radiotelephone;

receiving an average transmit power input representing the average transmit power;

amplifying the input signal in an amplifier to produce an amplified version of the input signal;

varying the impedance of an impedance network coupled to the amplifier responsive to a load control signal; and

generating a load control signal responsive to the input signal, the mode input, and the average power level, the mapping circuit generating the load control signal as a function of the average power level in a first mode and as function of the input signal envelope and the average power level in a second mode.

11. The method as defined in claim 10, wherein the step of generating the load control signal includes generating the load control signal as a function of substantially only the desired average power level in the first mode.

12. The method as defined in claim 11, wherein the step of generating the load control signal includes generating the load control signal responsive to the amplitude and phase of the input signal and the average transmit power in the second mode.

13. The method as defined in claim 10, wherein the step of generating the load control signal includes generating the load control signal as a function of the amplitude and phase of the input signal and the average transmit power in the second mode.

14. The method according to claim 13, wherein only a top portion of the AM envelope is used by the envelope mapping circuit to generate the load control signal.

15. The method according to claim 10, wherein step of varying the impedance comprises varying the impedance in discrete steps.

16. The method according to claim 10, further including the step of distorting the input signal before amplifying the input signal in the signal amplifier.

17. The method according to claim 10, further including the steps of monitoring the peak to average ratio of the amplified version of the input signal output and controlling the amplified version of the input signal to have a substantially constant peak to average ratio.

18. A load envelope following amplifier system, comprising:

a signal amplifier having an input and an output, the input for receiving an input signal having a amplitude modulation (AM) envelope, the amplifier for producing an amplified version of the input signal;

a variable impedance network coupled to the output the signal amplifier, the variable impedance network for presenting different impedances to the output of the signal amplifier responsive to a load control signal;

a signal quality detector coupled to impedance network and monitoring the peak to average ratio of the amplified version of the input signal output; and

an envelope mapping circuit coupled to the variable impedance network and the signal quality detector, the envelope detector generating the load control signal to cause the signal amplifier to produce the amplified version of the input signal with a substantially constant peak to average ratio.

19. The load envelope following amplifier system according to claim 18, wherein the envelope mapping circuit is responsive to at least the amplitude modulation envelope, the envelope mapping circuit producing the load control signal responsive to only a portion of the AM envelope.

20. The load envelope following amplifier system according to claim 19, wherein the portion of the envelope is the top portion of the AM envelope.

21. The load envelope following amplifier system according to claim 18, wherein the load control signal causes the variable impedance network to be varied in discrete steps.

22. The load envelope following amplifier system according to claim 18, wherein the variable impedance network includes a variable capacitance.

23. The load envelope following amplifier system according to claim 18, further including:

transmitting circuitry coupled to the input of the signal amplifier;

distortion control circuitry coupled to the envelope mapping circuit and the transmit circuitry, wherein the distortion control signal causes the transmit circuitry to impress distortion upon the input signal before the input signal is input to the signal amplifier.

24. The load envelope following amplifier system according to claim 18, further including a mode input, wherein the envelope mapping circuit generating the load control signal as a function of an average transmit power level control input in a first mode and as function of the input signal envelope and the average power level control input signal in a second mode.

25. The load envelope following amplifier system according to claim 24, wherein the step of generating the load control signal includes generating the load control signal dependent substantially only on the desired average power level in the first mode.