Polar modulation transmitter

• US 7,072,626 B2
• Filed: 04/30/2003
• Issued: 07/04/2006
• Est. Priority Date: 04/30/2003
• Status: Active Grant

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Hadjichristos, Aristotle
• Primary Examiner(s): Vo, Nguyen T.
• Assistant Examiner(s): Le, Nhan T.
• Application Number:
  US10/426,510
• Publication Number:
  US 20040219891A1
• Time in Patent Office: 1,161 Days
• Field of Search: 330/10, 330/149, 330/251, 330/295, 330/207, 330/136, 455/102, 455/116, 455/126, 455/91, 455/113, 455/115.1
• US Class Current: 455/126
• CPC Class Codes: H03F 1/0211 with control of the supply voltage or current
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• 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 3/24 of transmitter output stages
• CPC Class Codes: H04L 27/361 Modulation using a single or unspecified number of carriers, e.g. with separate stages of phase and amplitude modulation
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

A polar modulation transmitter circuit provides reduced ACPR in its output signal by controlling the relative delay between its envelope and phase modulation operations based on direct or indirect feedback measurement the output signal'"'"'s ACPR. Such measurement and associated control may be based on a delay controller that includes an ACPR measurement circuit and a delay control circuit. Additionally, or alternatively, the polar modulation transmitter circuit provides a greatly extended transmit power control range by using a staged amplifier circuit that includes a driver amplifier circuit operating in combination with a power amplifier circuit to impart desired envelope modulation. In an exemplary embodiment, the driver amplifier circuit is implemented as differential transistor pairs responsive to tail current modulation. As such, the driver amplifier circuit is suited in particular for economical and space saving integration within a transmitter or transceiver integrated circuit (IC).

Claims

1. A method of generating a radio frequency output signal based on polar modulation, the method comprising:

generating a phase-modulated signal responsive to an input phase-modulation information signal;

generating the output signal by imparting envelope-modulation to the phase-modulated signal responsive to an input envelope-modulation information signal;

measuring an adjacent channel power ratio (ACPR) for the output signal by feeding back a portion of the output signal via a feedback circuit that generates a baseband measurement signal, detecting an envelope of the baseband measurement signal over a first bandwidth to obtain a first detection signal, and detecting an envelope of the baseband measurement signal over a second bandwidth to obtain a second detection signal, and obtaining an ACPR measurement signal by subtracting the second detection signal from the first detection signal; and

controlling a relative delay between the phase-modulated and envelope-modulated information signals to reduce the measured ACPR.

2. The method of claim 1, wherein controlling the relative delay between the phase-modulated and envelope-modulated information signals to reduce the measured ACPR comprises adjusting a bandwidth of a filter used to filter one of the envelope modulation or the phase modulation information signals.

3. The method of claim 2, wherein adjusting the bandwidth comprises increasing or decreasing the bandwidth of the filter to reduce the measured ACPR.

4. The method of claim 1, wherein controlling the relative delay between the phase-modulated and envelope-modulated information signals to reduce the measured ACPR comprises adjusting a digital delay of one or both the phase-modulated and envelope-modulation information signals at a waveform generator that generates the phase-modulated and envelope-modulated information signals based on desired transmit signal data.

5. A method of generating a radio frequency output signal based on polar modulation, the method comprising:

generating a phase-modulated signal responsive to an input phase-modulation information signal;

generating the output signal by imparting envelope modulation to the phase-modulated signal in tandem using a tail-current modulated driver amplifier circuit responsive to a first scaled envelope modulation signal and a supply-modulated power amplifier circuit responsive to a second scaled envelope modulation signal; and

scaling an input amplitude modulation information signal by one or more scaling factors to generate the first and second scaled modulation signals as a function of the desired transmit power level.

6. The method of claim 5, wherein scaling an input amplitude modulation information signal by one or more scaling factors to generate the first and second scaled modulation signals as a function of an input power control signal corresponding to the desired transmit power level comprises:

in a first mode of operation, generating the first scaled envelope modulation signal as a steady state value and generating the second scaled envelope modulation signal as a scaled version of the input envelope modulation information signal; and

scaling the second scaled envelope modulation signal as a function of an input power control signal corresponding to the desired transmit power.

7. The method of claim 6, wherein scaling an input amplitude modulation information signal by one or more scaling factors to generate the first and second scaled modulation signals as a function of an input power control signal corresponding to the desired transmit power level further comprises:

in a second mode, generating the first and second scaled envelope modulation signals as scaled versions of the input envelope modulation information signal; and

scaling the first and second scaled envelope modulation signal as a function of an input power control signal corresponding to the desired transmit power.

8. The method of claim 7, further comprising operating in the first mode for a first range of transmit power control and operating in the second mode for a second, greater range of transmit power control.

9. The method of claim 5, further comprising implementing the driver amplifier circuit as a portion of a transmitter integrated circuit (IC), and implementing the power amplifier circuit separately from the transmitter IC, such that envelope modulation of the phase-modulated signal is achieved by coordinated operation of the transmitter IC and the power amplifier circuit.

10. The method of claim 5, further comprising:

measuring an adjacent channel power ratio (ACPR) for the output signal; and

controlling a relative delay between the input phase-modulation information signal and the input envelope-modulation information signal as a function of the measured ACPR to reduce the ACPR of the output signal.

11. A radio frequency polar modulation transmitter to generate a RF output signal at a desired transmit power, the transmitter_comprising:

a transmitter circuit that generates a phase-and-envelope modulated output signal based on separate phase-modulation and envelope-modulation information signals input to the transmitter circuit; and

a delay controller comprising a feedback circuit to obtain an analog feedback signal associated with the output signal of the transmitter, a measurement circuit, including first and second envelope detectors and an associated differencing amplifier, to generate an ACPR measurement signal based on the analog feedback signal, and a control circuit to generate a delay control signal responsive to the ACPR measurement signal, the delay controller configured to control a relative delay between the phase-modulation and envelope-modulation signals based on performing real-time ACPR measurement for the output signal.

12. The transmitter of claim 11, wherein the delay controller comprises a feedback controller operative to control a value of the delay control signal so as to reduce measured ACPR as indicated by the ACPR measurement signal.

13. The transmitter of claim 11, wherein the measurement circuit includes a filter associated with a first one of the envelope detectors that is operative to filter the feedback signal such that the first envelope detector receives feedback signal components corresponding to adjacent channel power in the output signal, and wherein a second one of the envelope detectors receives a full bandwidth version of the feedback signal.

14. The transmitter of claim 11, wherein the measurement circuit comprises:

an analog feedback circuit to obtain a feedback signal associated with the output signal;

a digitization circuit to obtain a digitized feedback signal from the analog feedback signal; and

a digital control circuit to obtain an ACPR measurement based on signal processing of the digitized feedback signal.

15. The transmitter of claim 14, wherein the digital control circuit is further operative to generate a delay control signal based on the ACPR measurement, and wherein the delay controller includes a digital delay element to control a relative delay between the phase-modulation information signal and the envelope-modulation information signal.

16. The transmitter of claim 11, wherein the transmitter circuit includes:

a phase modulation circuit to generate a phase-modulated signal responsive to the input phase-modulation information signal;

a staged saturated amplifier circuit comprising a driver amplifier circuit comprising differential transistor pairs that impart envelope modulation responsive to tail-current modulation, and further comprises a power amplifier circuit coupled to an output of the driver amplifier circuit that imparts envelope modulation responsive to supply signal modulation, the staged saturated amplifier circuit operative to generate the output signal by imparting envelope modulation to the phase-modulated signal responsive to scaled envelope modulation signals; and

a power controller to generate the scaled envelope modulation signals based on the input envelope-modulation information signal and an input power control signal.

17. The transmitter of claim 16, wherein the transmitter comprises a transmitter integrated circuit (IC) that includes the driver amplifier circuit, and further includes the power amplifier circuit implemented separately from the transmitter IC.

18. The transmitter of claim 16, wherein the power controller selectively controls whether the driver amplifier imparts envelope modulation by controlling whether the scaled envelope modulation signals provided to the driver amplifier are held at a steady state value or modulated according to the input envelope modulation information signal, such that the power amplifier circuit is used for envelope modulation in a first mode and both the power amplifier and driver circuit are used together to provide envelope modulation in a second mode.

19. The transmitter of claim 18, wherein the power controller operates in the first mode for a portion of a transmit power control range and operates in the second mode for a remaining portion of a transmit power control range.

20. A radio frequency polar modulation transmitter to generate a RF output signal at a desired transmit power, the transmitter comprising:

a phase modulator to generate a phase-modulated signal responsive to an input phase modulation information signal;

a staged saturated amplifier to generate the output signal by imparting envelope modulation to the phase-modulated signal;

said staged saturated amplifier comprising;

a driver amplifier circuit to impart envelope modulation to the phase-modulated signal responsive to a first scaled envelope modulation signal;

a power amplifier circuit coupled to the driver amplifier circuit to impart envelope modulation to the phase-modulated signal responsive to a second scaled envelope modulation signal; and

a power controller to generate the first and second scaled envelope modulation signals based on the input envelope modulation information signal and the desired transmit power.

21. The transmitter of claim 20, wherein the transmitter operates in a first mode wherein the driver amplifier circuit is operated as a pass-through circuit and only the power amplifier circuit is used to impart envelope modulation to the phase-modulated signal, and operates in a second mode wherein the driver amplifier circuit and the power amplifier circuit are operated in tandem to impart envelope modulation to the phase-modulated signal.

22. The transmitter of claim 21, wherein the first mode is active for a first range of transmit power control, and wherein the second mode is active for a second, greater range of transmit power control.

23. The transmitter of claim 21, wherein the transmitter is configured to support EDGE-format transmissions and WCDMA-format transmissions, and wherein the transmitter operates in the first mode for EDGE-format transmissions and operates in the second mode for WCDMA-transmissions.

24. The transmitter of claim 21, wherein the transmitter is configured to support WCDMA-format transmissions, and wherein the transmitter operates in the first mode for a first portion of a required transmit power control range, and operates in the second mode, as needed, for a remaining portion of the required transmit power control range.

25. The transmitter of claim 20, wherein the driver amplifier circuit comprises a tail-current modulated differential transistor pair operated in saturated mode.

26. The transmitter of claim 25, wherein the differential transistor pair includes a differential input coupled to a quadrature output of the phase modulator, and includes a differential output coupled to an input of the power amplifier circuit.

27. The transmitter of claim 25, wherein the differential transistor pair is operative to pass-through the phase-modulated signal for envelope modulation by the power amplifier circuit if the first scaled envelope modulation signal is held at a steady state, and is operative to impart envelope modulation in tandem with the power amplifier circuit if the first scaled envelope modulation signal is made responsive to the input envelope-modulation information signal.

28. A radio frequency polar modulation transmitter to generate a RF output signal at a desired transmit power, the transmitter comprising:

a phase modulator to generate a phase-modulated signal responsive to an input phase-modulation information signal;

a staged amplifier circuit comprising a driver amplifier circuit to impart envelope modulation to the phase-modulated signal responsive to a first scaled envelope modulation signal, a power amplifier circuit to impart envelope modulation to the phase-modulated signal responsive to a modulated supply signal, a power amplifier controller to generate the modulated supply signal responsive to a second scaled envelope modulation signal, and a power controller to generate the first and second scaled envelope modulation signals responsive to an input envelope-modulation information signal and based on the desired transmit power, the staged amplifier circuit configured to generate an output signal by imparting envelope modulation to the phase-modulated signal responsive to an input amplitude modulation information signal; and

a delay controller to control a relative delay between the input phase-modulation and envelope-modulation information signals responsive to a measured adjacent channel power ratio (ACPR) of the output signal.

29. The transmitter of claim 28, wherein the driver amplifier and power amplifier circuits operate in tandem to impart synchronized envelope modulation to the phase-modulated signal.