Dual open and closed loop linear transmitter

• US 6,606,483 B1
• Filed: 10/10/2000
• Issued: 08/12/2003
• Est. Priority Date: 10/10/2000
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Gailus, Paul H., Baker, Michael H., Turney, William J.
• Primary Examiner(s): Tran, Pablo N
• Application Number:
  US09/686,732
• Time in Patent Office: 1,036 Days
• Field of Search: 455/126, 455/127, 455/115, 455/91, 455/116, 455/114, 455/102, 455/104, 455/108, 455/109, 455/111, 455/113, 455/118, 455/119, 455/125, 455/69, 330/129, 330/136, 330/284, 330/103, 330/107, 330/110, 330/149, 330/109
• US Class Current: 455/126
• CPC Class Codes: H03F 1/0277 Selecting one or more amplifiers from a plurality of amplifiers
• CPC Class Codes: H03F 1/345 using hybrid or directional couplers
• CPC Class Codes: H03G 3/3047 for intermittent signals, e.g. burst signals
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence

Abstract

A linear transmitter includes an amplifier feedback loop for amplifying an input signal at a power amplifier. The feedback loop is operated in an open loop mode when the power amplifier is operating at a first operating point and is operated in a closed loop mode when the power amplifier is operating at a second operating point. The transmitter further includes an auxiliary loop coupled to the amplifier feedback loop that provides phase training for the feedback loop and power leveling when the feedback loop is operating open loop. Open loop phase training and power leveling is done during open loop transmission, without an associated training signal or training period. Stable closed loop operation can commence subsequently providing the higher power amplifier efficiency associated with the second operating point and maintaining off channel interference requirements.

Claims

1. A linear transmitter comprising:

an amplifier feedback loop comprising;

a power amplifier that receives and amplifies an input signal to produce an output signal, wherein the power amplifier comprises an input port and an output port;

a feedback circuit coupled to the output port of the power amplifier that samples the output signal to produce a sampled output signal;

a plurality of switching devices that couple the feedback circuit to, and decouple the feedback circuit from, the input port of the power amplifier;

an auxiliary loop coupled to the amplifier feedback loop that receives the sampled output signal from the feedback loop, compares the sampled output signal to a desired input signal, determines a phase error based on the comparison of the sampled output signal to the desired input signal, and aligns a phase of the sampled output signal with a phase of the input signal based on the phase error; and

wherein the power amplifier operates at a first operating point when decoupled at the input port from the feedback circuit, wherein the power amplifier operates at a second operating point when coupled at the input port to the feedback circuit, and wherein the first operating point is different than the second operating point.

2. The linear transmitter of claim 1, wherein the auxiliary loop further produces a control signal based on the phase error, and wherein the linear transmitter further comprises a phase adjustment circuit coupled between the auxiliary loop and the feedback circuit that receives the control signal from the auxiliary loop and adjusts a phase of the feedback circuit based on the control signal.

3. The linear transmitter of claim 1, wherein the auxiliary loop comprises:

a magnitude detection module that receives a desired input signal, detects a magnitude of the desired input signal, and conveys the detected magnitude to an adapter module;

a delay module that that receives a desired input signal and adds a phase delay to the desired input signal to produce a phase delayed desired input signal;

an offset and scale module that receives the sampled output signal and produces a magnitude scaled and offset adjusted sampled output signal in response to a magnitude adjustment signal and a DC offset adjustment signal received from the adapter module;

a summing junction module in communication with the offset and scale module and the delay module that receives the phase delayed desired input signal, receives magnitude scaled and offset adjusted sampled output signal from the offset and scale module, and sums the phase delayed desired input signal and the magnitude scaled and offset adjusted sampled output signal to produce an error signal; and

an adapter module in communication each of the offset and scale module, the delay module, the magnitude detection module, and the summing junction module, that receives the phase delayed desired input signal, receives the detected magnitude of the desired input signal from the magnitude detection module, receives the error signal from the summing junction, determines a magnitude adjustment signal based on the magnitude of the desired input signal, determines a DC offset adjustment signal based on the error signal, and produces a control signal based on the error signal.

4. The linear transmitter of claim 3, wherein the control signal comprises a phase control signal and a magnitude control signal.

5. The linear transmitter of claim 4, further comprising a scaling attenuator coupled to the amplifier feedback loop and to the auxiliary loop, wherein the scaling attenuator receives an input signal sourced by an information source, receives the magnitude error control signal from the auxiliary loop, attenuates the input signal based on the magnitude control signal, and conveys the attenuated input signal to the amplifier feedback loop, and wherein the drive signal received by the power amplifier is based on the attenuated input signal.

6. The linear transmitter of claim 1, wherein the power amplifier comprises a plurality of input ports, wherein a first input port of the plurality of input ports receives a drive signal and is coupled to the feedback circuit via at least one switching device of the plurality of switching devices, and wherein a second input port of the plurality of input ports receives a control signal that controls the operating point of the power amplifier.

7. The linear transmitter of claim 6, further comprising a power amplifier efficiency circuit coupled to the second input port that sources a first supply voltage and a first supply current and a second supply voltage and a second supply current to the power amplifier, wherein the first supply voltage and the first supply current establish the first operating point of the power amplifier, wherein the second supply voltage and the second supply current establish the second operating point of the power amplifier, and wherein the first operating point is different than the second operating point.

8. The linear transmitter of claim 6, further comprising a power amplifier efficiency circuit coupled to the second input port that sources a first bias voltage and a first bias current and a second bias voltage and a bias supply current to the power amplifier, wherein the first bias voltage and the first bias current establish the first operating point of the power amplifier, wherein the second bias voltage and the second bias current establish the second operating point of the power amplifier, and wherein the first operating point is different than the second operating point.

9. The linear transmitter of claim 1, wherein the auxiliary loop phase trains the feedback circuit when the feedback circuit is decoupled from the input port of the power amplifier.

10. The linear transmitter of claim 1, wherein the power amplifier comprises a radio frequency (RF) amplifying element and an output matching circuit, wherein the output matching circuit presents an adjustable load to the RF amplifying element, and wherein the first operating point is established by adjusting the adjustable load to a first complex impedance and wherein the second operating point is established by adjusting the adjustable load to a second complex impedance.

11. The linear transmitter of claim 1, further comprising a plurality of power amplifier load circuits, wherein each power amplifier load circuit of the plurality of power amplifier load circuits is capable of being coupled to, and decoupled from, the output port of the power amplifier, wherein each power amplifier load circuit comprises a complex impedance circuit, wherein the first operating point is established by coupling a first power amplifier load circuit of the plurality of power amplifier load circuits to the output port, and wherein the second operating point is established by coupling a second power amplifier load circuit of the plurality of power amplifier load circuits to the output port.

12. The linear transmitter of claim 1, wherein the power amplifier comprises a plurality of radio frequency (RF) amplifying elements, wherein each RF amplifying element of the plurality of RF amplifying elements is capable of being coupled to, and decoupled from, the amplifier feedback loop, wherein each RF amplifying element is biased at a bias level different from the other RF amplifying elements, wherein the first operating point is established by coupling a first RF amplifying element of the plurality of RF amplifying elements to the feedback loop, and wherein the second operating point is established by coupling a second RF amplifying element of the plurality of RF amplifying elements to the feedback loop.

13. The linear transmitter of claim 1, wherein the power amplifier comprises a plurality of radio frequency (RF) amplifying elements, wherein each RF amplifying element of the plurality of RF amplifying elements is capable of being coupled to, and decoupled from, the feedback loop, wherein each RF amplifying element includes an output matching circuit, wherein the output matching circuit associated with each RF amplifying element presents a load to the RF amplifying element that is different from the load presented by the other output matching circuits to each of the other RF amplifying elements, wherein the first operating point is established by coupling a first RF amplifying element of the plurality of RF amplifying elements to the feedback loop, and wherein the second operating point is established by coupling a second RF amplifying element of the plurality of RF amplifying element to the feedback loop.

14. The linear transmitter of claim 1, wherein the auxiliary loop further determines a phase change of the linear transmitter that corresponds to a change in a transmit frequency of the linear transmitter and, when the linear transmitter changes from a first transmit frequency to a second transmit frequency, aligns a phase of the sampled output signal with a phase of the input signal based on the determined phase change.

15. A communication device comprising:

an information source that sources an input signal;

an amplifier feedback loop coupled to the information source that comprises;

a power amplifier that receives and amplifies the input signal to produce an output signal, wherein the power amplifier comprises an input port and an output port;

a feedback circuit coupled to the output port of the power amplifier that samples the output signal to produce a sampled output signal;

a plurality of switching devices that couple the feedback circuit to, and decouple the feedback circuit from, the input port of the power amplifier;

an auxiliary loop coupled to the information source and to the amplifier feedback loop that receives the sampled output signal from the feedback loop, compares the sampled output signal to a desired input signal, determines a phase error based on the comparison of the sampled output signal to the desired input signal, and aligns a phase of the sampled output signal with a phase of the input signal based on the phase error;

a processor coupled to the amplifier feedback loop and to the auxiliary loop that couples and decouples the feedback circuit to the power amplifier by controlling each switching device of the plurality of switching devices; and

wherein the power amplifier operates at a first operating point when decoupled at the input port from the feedback circuit, wherein the power amplifier operates at a second operating point when coupled at the input port to the feedback circuit, and wherein the first operating point is different from the second operating point.

16. The communication device of claim 15, further comprising a power amplifier efficiency circuit coupled to the processor and to the power amplifier that sources a first supply voltage and a first supply current and a second supply voltage and a second supply current to the power amplifier in response to control signals received from the processor, wherein the first supply voltage and the first supply current establish the first operating point of the power amplifier, wherein the second supply voltage and the second supply current establish the second operating point of the power amplifier, and wherein the first operating point is different than the second operating point.

17. The communication device of claim 15, wherein the auxiliary loop further determines a phase change of the linear transmitter that corresponds to a change in a transmit frequency of the linear transmitter and, when the linear transmitter changes from a first transmit frequency to a second transmit frequency, aligns a phase of the sampled output signal with a phase of the input signal based on the determined phase change.

18. A method for amplifying a radio frequency signal in a transmitter having a feedback loop that comprises a forward path coupled to a feedback path, wherein the forward path comprises a power amplifier, the method comprising steps of:

receiving a first input signal;

amplifying the first input signal while operating the power amplifier at a first operating point and with the feedback loop open to produce a first output signal;

closing the feedback loop;

adjusting the first operating point of the power amplifier to produce a second operating point, wherein the second operating point is different than the first operating point;

receiving a second input signal;

amplifying the second input signal while operating the power amplifier at the second operating point and with the feedback loop closed to produce a second output signal.

19. The method of claim 18, wherein the first operating point is a higher linearity operating point than the second operating point.

20. The method of claim 18, further comprising a step of phase training the feedback loop when the feedback loop is open.

21. The method of claim 20, wherein the step of phase training comprises steps of:

sampling the first output signal to produce a sampled output signal;

comparing the sampled output signal to a desired input signal;

determining a phase error based on the comparison of the sampled output signal and the desired input signal; and

adjusting a phase of the feedback path based on the phase error.

22. The method of claim 21, wherein the step of adjusting a phase of the feedback path based on the phase error comprises steps of:

producing a control signal based on the phase error; and

adjusting a phase of a reference signal based on the control signal, wherein the reference signal is used to downconvert a signal in the feedback path.

23. The method of claim 21, wherein the step of comparing the sampled output signal to a desired input signal comprises steps of:

determining a magnitude of a desired input signal;

scaling a magnitude of the sampled output signal based on the determined magnitude of the desired input signal;

adjusting a direct current offset of the sampled output signal; and

comparing the magnitude scaled and direct current offset adjusted sampled output signal to the desired input signal.

24. The method of claim 18, further comprising a step of power level setting the transmitter while the transmitter is operating with the feedback loop open.

25. The method of claim 18, further comprising steps of:

determining a phase change of the linear transmitter that corresponds to a transmit frequency change of the linear transmitter; and

when the linear transmitter changes from a first transmit frequency to a second transmit frequency, adjusting a phase of the feedback path based on the determined phase change.