Polar loop radio frequency (RF) transmitter having increased dynamic range amplitude control

• US 7,787,570 B2
• Filed: 07/13/2005
• Issued: 08/31/2010
• Est. Priority Date: 07/13/2005
• Status: Active Grant

• Current Assignee: Skyworks Solutions Incorporated
• Original Assignee: Skyworks Solutions Incorporated
• Inventors: Rozenblit, Dmitriy, Sowlati, Tirdad, Damgaard, Morten
• Primary Examiner(s): Payne; David C
• Assistant Examiner(s): Shah; Tanmay K
• Application Number:
  US11/180,940
• Publication Number:
  US 20070014381A1
• Time in Patent Office: 1,875 Days
• Field of Search: 375/320, 375/149, 455/234.1, 455/126, 330/149
• US Class Current: 375/320
• CPC Class Codes: H03C 1/00 Amplitude modulation H03C5/00, H03C7/00 take precedence
• CPC Class Codes: H03G 3/3047 for intermittent signals, e.g. burst signals
• CPC Class Codes: H04L 27/08 Amplitude regulation arrangements
• 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 27/3809 Amplitude regulation arrangements
• CPC Class Codes: H04W 52/06 TPC algorithms
• CPC Class Codes: H04W 52/36 with a discrete range or set of values, e.g. step size, ramping or offsets

Abstract

A closed loop power control system for a radio frequency (RF) transmitter comprises a first variable gain element located in a power control loop and configured to receive a power level signal and an inverse representation of a power control signal, a second variable gain element located in the power control loop and configured to receive an error signal and the power control signal, and a third variable gain element configured to receive an amplitude modulated (AM) signal and the power control signal, the third variable gain element having a gain characteristic configured to operate to reduce the gain applied to the AM signal when the power control signal falls below a minimum predetermined value, and to provide the AM signal as a reference signal.

Claims

1. A method for controlling an amplitude-modulated signal supplied to a power control loop, comprising:

receiving, in a first variable gain element, a power level signal and an inverse representation of a power control signal;

receiving, in a second variable gain element, an error signal and the power control signal, the error signal generated by a comparator inserted between the first variable gain element and the second variable gain element; and

receiving, in a third variable gain element coupled between a modulator and the comparator, an amplitude-modulated (AM) signal and the power control signal, the third variable gain element having a gain characteristic configured to reduce the gain applied to the AM signal when the power control signal falls below a minimum predetermined value, the third variable gain element configured to provide the AM signal as a reference signal with a constant (average) level for the power control loop.

2. The method of claim 1, further comprising providing the gain characteristic of the third variable gain element as a soft step function.

3. The method of claim 2, further comprising providing the gain characteristic of the third variable gain element to operate during power ramp-up and power ramp-down of a power amplifier associated with the RF transmitter.

4. The method of claim 3, further comprising supplying the AM signal to the third variable gain element directly from a modulator.

5. The method of claim 4, in which the total variable gain range is approximately 70 decibels (dB).

6. The method of claim 5, wherein the variable gain element is a variable gain amplifier having a maximum gain when the power control signal is at the minimum predetermined value.

7. The method of claim 6, wherein the gain of the variable gain amplifier is reduced when the power control signal falls below the minimum predetermined value.

8. A closed loop power control system for a radio frequency (RF) transmitter, comprising:

a first variable gain element located in a power control loop and configured to receive a power level signal and an inverse representation of a power control signal;

a second variable gain element located in the power control loop and configured to receive an error signal and the power control signal; and

a third variable gain element coupled between a modulator and a comparator within the closed loop power control system, the third variable gain element configured to receive an amplitude-modulated (AM) signal and the power control signal, the third variable gain element having a gain characteristic configured to reduce the gain applied to the AM signal when the power control signal falls below a minimum predetermined value, and to provide the AM signal as a reference signal with a constant (average) level for the power control loop.

9. The system of claim 8, wherein the third variable gain element is a variable gain amplifier.

10. The system of claim 9, wherein the gain characteristic of the variable gain amplifier is a soft step function.

11. The system of claim 10, wherein the gain characteristic of the variable gain amplifier operates during power ramp-up and power ramp-down of a power amplifier associated with the RF transmitter.

12. The system of claim 11, wherein the AM signal is supplied to the variable gain amplifier directly from a modulator.

13. The system of claim 12, in which the total variable gain range is approximately 70 decibels (dB).

14. The system of claim 13, wherein the variable gain amplifier has a maximum gain when the power control signal is above the minimum predetermined value.

15. The system of claim 14, wherein the gain of the variable gain amplifier is reduced when the power control signal falls below the minimum predetermined value.

16. A portable transceiver having a closed loop power control system for a radio frequency (RF) transmitter, comprising:

transmit and receive circuitry;

a first variable gain element located in a power control loop and configured to receive a power level signal and an inverse representation of a power control signal;

a second variable gain element located in the power control loop and configured to receive an error signal and the power control signal; and

a third variable gain element coupled between a modulator and a comparator within the closed loop power control system, the third variable gain element configured to receive an amplitude-modulated (AM) signal and the power control signal, the third variable gain element having a gain characteristic configured to reduce the gain applied to the AM signal when the power control signal falls below a minimum predetermined value, and to provide the AM signal as a reference signal with a constant (average) level for the power control loop.

17. The system of claim 16, wherein the third variable gain element is a variable gain amplifier.

18. The system of claim 17, wherein the gain characteristic of the variable gain amplifier is a soft step function and operates during power ramp-up and power ramp-down of a power amplifier associated with the RF transmitter.

19. The system of claim 18, wherein the variable gain amplifier has a maximum gain when the power control signal is above the minimum predetermined value.

20. The system of claim 19, wherein the gain of the variable gain amplifier is reduced when the power control signal falls below the minimum predetermined value.