Configurable load impedance for power amplifier pre-distortion calibration
An integrated circuit radio transceiver and method therefor includes an integrated circuit radio transceiver operable to provide specified gain levels and transmit path filter responses to correspond with a selected power spectral density mask. Changes in gain may be provided solely digital gain changes or may include analog gain module gain changes. A transmitter selects from one of at least three masks to reduce or eliminate spectral regrowth out of band to satisfy EVM requirements. Circuitry is provided to allow a transceiver to determine in advance what pre-distortion compensation settings are required for the various gain settings.
1. A method of operating an integrated circuit radio transceiver to produce an outgoing Radio Frequency (RF) signal comprising:
selecting a pre-distortion setting from a plurality of pre-determined pre-distortion settings;
producing an outgoing digital signal using outgoing data and the pre-distortion setting;
producing the RF signal based upon the outgoing digital signal;
amplifying the RF signal by a power amplifier;
coupling a specified load to the power amplifier output;
enabling a receive path;
coupling the receive path to the power amplifier output;
receiving the RF frequency signal via the receive path, the receive path different from a feedback path that carries the feedback signal;
determining the plurality of pre-determined pre-distortion settings using the receive path;
measuring a voltage standing wave ratio of a feedback signal produced at the power amplifier output;
selecting a different pre-distortion setting from the plurality of pre-determined pre-distortion settings based upon the voltage standing wave ratio; and
decoupling the specified load and coupling an antenna to the power amplifier output to radiate the RF signal.
2. The method of claim 1 , wherein the specified load is a 50 ohm load.
3. The method of claim 1 , further comprising, during a transmit mode of operation with the antenna coupled to the power amplifier output to radiate the RF signal, altering the pre-distortion settings based upon the feedback signal.
4. The method of claim 1 , further comprising adjusting a gain setting of one of a filter, a mixer, and a signal amplifier in a transmit path corresponding to the pre-distortion setting.
5. The method of claim 1 , wherein:
the transceiver is operable to support OFDM modulation; and
the pre-distortion settings are determined based upon OFDM modulation parameters.
6. The method of claim 1 , wherein:
the transceiver is a MIMO transceiver and includes multiple transmit paths; and
pre-distortion settings are determined for the multiple transmit paths.
7. The method of claim 1 further comprising determining a plurality of power spectral density masks to employ as the plurality of pre-determined pre-distortion settings.
8. The method of claim 1 , further comprising:
adjusting at least one analog transmit path gain setting; and
for each gain setting, determining a pre-distortion setting for selection during a transmit mode of operation.
9. The method of claim 1 , wherein the RF signal is one of a Wireless Local Area Network (WLAN) signal and a cellular network signal.
10. An integrated circuit radio transceiver operable to support wireless communications, comprising:
processing circuitry operable to:
select a pre-distortion setting from a plurality of pre-determined settings; and
produce an outgoing digital signal using the pre-distortion setting;
analog transmit path circuitry including up-conversion circuitry and a power amplifier and operable to produce a Radio Frequency (RF) signal based upon the outgoing digital signal;
a feedback path coupled between the power amplifier output and the processing circuitry;
coupling circuitry operable to couple an antenna to the power amplifier output during transmit operations and to couple a specified load to the power amplifier output during calibration operations;
wherein during calibration operations, the processing circuitry is operable to:
measure a voltage standing wave ratio of a feedback signal produced at the power amplifier output via a feedback path;
receive the RF signal via the receive path, the receive path different than the feedback path; and
determine the plurality of pre-determined pre-distortion settings using the receive path; and
select a different pre-distortion setting from the plurality of pre-determined pre-distortion settings based upon the voltage standing wave ratio.
11. The integrated circuitry radio transceiver of claim 10 , wherein the specified load is a 50 ohm load.
12. The integrated circuitry radio transceiver of claim 10 , wherein the processing circuitry is further operable to, during transmit operation, alter the pre-distortion settings based upon the feedback signal.
13. The integrated circuitry radio transceiver of claim 10 , wherein the processing circuitry is further operable to adjust a gain setting of at least one component of the transmit path corresponding to the pre-distortion setting.
14. The integrated circuitry radio transceiver of claim 10 , wherein:
the transceiver is operable to support OFDM modulation; and
the pre-distortion settings are determined based upon OFDM parameters.
15. The integrated circuitry radio transceiver of claim 10 , wherein:
the transceiver is a MIMO transceiver and includes multiple transmit paths; and
the pre-distortion settings are determined for each of the multiple transmit paths.
16. The integrated circuitry radio transceiver of claim 10 , wherein the processing circuitry is further operable to determine a plurality of power spectral density masks to employ as the plurality of pre-determined pre-distortion settings.
17. The integrated circuitry radio transceiver of claim 10 , wherein the processing circuitry is further operable to:
adjust at least one analog transmit path gain setting; and
for each gain setting, determine a pre-distortion setting for selection during transmit mode of operations.
18. The integrated circuit radio transceiver of claim 10 , wherein the RF signal is one of a Wireless Local Area Network (WLAN) signal and a cellular network signal.
19. An integrated circuit radio transceiver operable to support wireless communications, comprising:
processing circuitry operable to produce an outgoing digital signal:
analog transmit path circuitry including up-conversion circuitry and a power amplifier and operable to produce a Radio Frequency (RF) signal based upon the outgoing digital signal;
a receive path;
a feedback path coupled between the power amplifier output and the processing circuitry;
coupling circuitry operable to couple an antenna to the power amplifier output during transmit operations and to couple a specified load to the power amplifier output during calibration operations;
wherein during calibration operations, the processing circuitry is operable to:
receive the RF signal via the receive path, the receive path different than the feedback path; and
determine a plurality of pre-determined pre-distortion settings using the receive path; and
select one of the plurality of pre-determined pre-distortion setting based upon a feedback signal received via the feedback path.
20. The integrated circuitry radio transceiver of claim 19 , wherein the processing circuitry is further operable to, during transmit operation, alter the pre-distortion settings based upon the feedback signal.