Method and apparatus for optimizing supply modulation in a transmitter
View Patent ↗A transmitter ( 200 ) has a compression detector for sensing the level of compression ( 110 ) in a signal that is being transmitted. The transmitter also has a radio frequency power amplifier (RFPA) ( 414 ) that is supplied by a supply modulator ( 426 ). The supply modulator provides a dynamic supply bias to the RFPA to maintain a desired amount of compression in the signal being transmitted. The supply modulator is responsive to a modulation signal ( 207 ) created by substantially following the envelope ( 214 ) of the signal to be transmitted ( 212 ). However, various signal and operational conditions can occur which cause the compression level to deviate ( 506 ) from the desired level. To maintain the desired compression level, the compression detector provides an output that is used to adjust the modulation signal from following the envelope of the signal to be transmitted in an unadjusted manner.
1. A method for optimizing supply modulation in a transmitter, comprising:
providing a signal to be transmitted, the signal having an envelope;
providing a modulation signal to a power regulator, the power regulator for providing a supply voltage to a radio frequency power amplifier (RFPA), the modulation signal substantially corresponding to the envelope of the signal to be transmitted;
comparing an actual signal to be transmitted by the RFPA with an expected signal at a point in the transmitter wherein said expected signal is determined by calculation, or by mapping with a look-up table; and
adjusting the modulation signal after said comparing step in response to detecting a deviation of the actual signal to be transmitted from the expected signal to maintain a desired compression level of the RFPA.
2. A method for optimizing supply modulation as defined in claim 1 , further comprising linearizing the signal to be transmitted.
3. A method for optimizing supply modulation as defined in claim 2 , wherein the linearizing comprises linearizing by cartesian feedback.
4. A method for optimizing supply modulation as defined in claim 3 , wherein the comparing comprises comparing reference baseband signals with summed baseband signals.
5. A method for optimizing supply modulation as defined in claim 1 , wherein the comparing comprises comparing a low level RF signal with an amplified RF signal at the input and output, respectively, of the RFPA.
6. A method for optimizing supply modulation as defined in claim 1 , wherein the comparing is performed by a digital signal processor.
7. A transmitter for optimizing a supply modulation, comprising:
a radio frequency power amplifier (RFPA) for amplifying a low level RF signal and providing an amplified RF signal;
a power supply for providing power to the RFPA in correspondence with a modulation signal supplied to the power supply;
a means for generating an envelope of a signal to be transmitted and providing the modulation signal to the power supply, the modulation signal substantially corresponding to the envelope of the signal to be transmitted; and
a means for comparing an actual signal to be transmitted by the RFPA with an expected signal at a point in the transmitter wherein said expected signal is determined by calculation, or by mapping with a look-up table; and
wherein the modulation signal after said comparing step is adjusted in response to detecting a deviation of the actual signal to be transmitted from the expected signal to maintain a desired compression level of the RFPA.
8. A transmitter for optimizing a supply modulation as defined in claim 7 , further comprising means for linearizing the signal to be transmitted.
9. A transmitter for optimizing a supply modulation as defined in claim 8 , wherein the means for linearizing comprises cartesian feedback.
10. A transmitter for optimizing a supply modulation as defined in claim 9 , wherein the means for comparing compares reference baseband signals with summed baseband signals in the transmitter.
11. A transmitter for optimizing a supply modulation as defined in claim 7 , wherein the means for comparing compares a low level RF signal with an amplified RF signal at the input and output, respectively, of the RFPA.
12. A transmitter for optimizing a supply modulation as defined in claim 7 , wherein the means for comparing comprises a digital signal processor.
13. A method of modulating a supply voltage supplied to a radio frequency power amplifier (RFPA) in a transmitter, comprising:
providing a signal to be transmitted, the signal having an envelope;
providing a modulation signal to a power regulator, the power regulator for providing the supply voltage to said RFPA, the modulation signal substantially corresponding to the envelope of the signal to be transmitted; and
adjusting the modulation signal after comparing an actual output signal of said RFPA with an expected signal wherein said expected signal is determined by calculation, or by mapping with a look-up table; to avoid excess gain compression at a gain stage of the transmitter, wherein adjusting the modulation signal deviates the modulation signal from autonomous correspondence with the envelope of the signal to be transmitted.
14. A method of modulating a supply voltage as defined in claim 13 , further comprising linearizing the signal to be transmitted.
15. A method of modulating a supply voltage as defined in claim 14 , wherein the linearizing comprises linearizing by cartesian feedback.
16. A method of modulating a supply voltage as defined in claim 15 , wherein adjusting the modulation signal comprises comparing reference baseband signals with summed baseband signals.
17. A method of modulating a supply voltage as defined in claim 13 , wherein adjusting the modulation signal comprises comparing a low level RF signal with an amplified RF signal at the input and output, respectively, of the RFPA.
18. A method of modulating a supply voltage as defined in claim 16 , wherein the comparing is performed by a digital signal processor.