Controlling a Power Amplifier Based on Transmitter Output Emissions

• US 20130107926A1
• Filed: 06/07/2012
• Published: 05/02/2013
• Est. Priority Date: 06/08/2011
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Dakshinamurthy, Sriraman, Lorenz, Robert, Xia, Ying
• Granted Patent: US 8,879,665 B2
• Time in Patent Office: Days
• US Class Current: 375/224
• CPC Class Codes: H03F 1/0233 by using a signal derived from the output signal, e.g. bootstrapping the voltage supply
• CPC Class Codes: H03F 1/0255 by using a signal derived from the output signal
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04

Abstract

Methods and systems for controlling the supply voltage provided to a power amplifier (PA) in a radio frequency (RF) transmitter based on measured output spectrum emissions are provided. In an embodiment, the PA supply voltage is adjusted such that spectrum emission limits are satisfied with predetermined margins. In another embodiment, the predetermined margins are reduced to lower power consumption of the PA.

Claims

1. A method for controlling a power amplifier (PA) in a radio frequency (RF) transmitter, comprising:

performing one or more spectrum emission measurements at an output of the RF transmitter;

comparing the one or more spectrum emission measurements to a spectrum emission limit; and

adjusting a supply voltage to the PA based on the comparison of the one or more spectrum emission measurements to the spectrum emission limit.

2. The method of claim 1, wherein the one or more spectrum emission measurements include out-of-band emission measurements at one or more spectral mask corner frequencies.

3. The method of claim 1, wherein the one or more spectrum emission measurements include an in-channel emission measurement and an adjacent channel emission measurement.

4. The method of claim 1, wherein the one or more spectrum emission measurements include a first emission measurement and a second emission measurement, the first emission measurement corresponding to a first frequency bin centered at an offset frequency above a center frequency of an assigned channel bandwidth, and the second emission measurement corresponding to a second frequency bin centered at the offset frequency below the center frequency of the assigned channel bandwidth.

5. The method of claim 1, further comprising:

computing a difference between at least one spectrum emission measurement of the one or more spectrum emission measurements and the spectrum emission limit to generate a current margin between the at least one spectrum emission measurement and the spectrum emission limit; and

comparing the current margin to a minimum desired margin.

6. The method of claim 5, further comprising:

if the current margin is lower than the minimum desired margin, increasing the supply voltage to the PA; and

if the current margin exceeds the minimum desired margin by a predefined threshold, decreasing the supply voltage to the PA.

7. The method of claim 6, further comprising:

determining, based on the comparison of the current margin to the minimum desired margin, an amount of desired increase or decrease of the current margin; and

increasing or decreasing the supply voltage to the PA based on the amount of desired increase or decrease of the current margin.

8. The method of claim 5, wherein the spectrum emission limit is a spectral mask emission limit.

9. The method of claim 1, wherein the one or more spectrum emission measurements include an in-channel emission measurement and an adjacent channel emission measurement, the method further comprising:

computing a ratio of the in-channel emission measurement to the adjacent channel emission measurement;

computing a difference between the ratio and the spectrum emission limit to generate a current margin; and

comparing the current margin to a minimum desired margin.

10. The method of claim 9, wherein the spectrum emission limit is an Adjacent Channel Leakage Ratio (ACLR) limit.

11. A radio frequency (RF) transmitter, comprising:

a digital module configured to generate baseband in-phase (I) and quadrature-phase (Q) signals of a desired output waveform;

a filtering and up-conversion module configured to generate a RF signal from the baseband I and Q signals;

a power amplifier (PA) configured to power amplify the RF signal to generate an output signal of the RF transmitter; and

a feedback path comprising;

a RF receiver configured to receive the output signal of the RF transmitter and to generate feedback I and Q signals; and

a spectrum measurement module configured to generate one or more spectrum emission measurements of the output signal based on the feedback I and Q signals,

wherein the digital module is further configured to control a supply voltage of the PA based on at least one of the one or more spectrum emission measurements.

12. The RF transmitter of claim 11, wherein the RF receiver of the feedback path includes a directional coupler, coupled to an output of the PA.

13. The RF transmitter of claim 11, further comprising:

a power supply configured to receive a control signal from the digital module and to control the supply voltage of the PA in accordance with the control signal.

14. The RF transmitter of claim 11, wherein the digital module is further configured to compare at least one spectrum emission measurement of the one or more spectrum emission measurements to a spectrum emission limit.

15. The RF transmitter of claim 11, wherein the digital module is further configured to compute a difference between the least one spectrum emission measurement and the spectrum emission limit to generate a current margin between the at least one spectrum emission measurement and the spectrum emission limit;

and to compare the current margin to a minimum desired margin.

16. The RF transmitter of claim 15, wherein the digital module is further configured to increase the supply voltage to the PA if the current margin is lower than the minimum desired margin, and to decrease the supply voltage to the PA if the current margin exceeds the minimum desired margin by a predefined threshold.

17. The RF transmitter of claim 11, wherein the one or more spectrum emission measurements include an in-channel emission measurement and an adjacent channel emission measurement.

18. The RF transmitter of claim 11, wherein the one or more spectrum emission measurements include a first emission measurement and a second emission measurement, the first emission measurement corresponding to a first frequency bin centered at an offset frequency above a center frequency of an assigned channel bandwidth of the RF transmitter, and the second emission measurement corresponding to a second frequency bin centered at the offset frequency below the center frequency of the assigned channel bandwidth.

19. A method for controlling a power amplifier (PA) in a radio frequency (RF) transmitter, comprising:

performing a spectrum emission measurement based on an output of the PA; and

adjusting at least one input to the PA based on the spectrum emission measurement.

20. The method of claim 19, wherein the at least one input to the PA includes one or more of a supply voltage of the PA, a bias setting of the PA, and a gain setting of the PA.