Lookup table calibration apparatus and method
A lookup table calibration apparatus and method are disclosed. The lookup table calibration apparatus includes a power amplifier circuit configured to amplify a radio frequency (RF) signal having time-variant power levels based on a modulated voltage. To ensure proper alignment between the modulated voltage and the time-variant power levels, the power amplifier circuit is further configured to phase-shift the RF signal based on a modulated phase correction voltage. Specifically, the modulated voltage is generated based on a modulated voltage lookup table and the modulated phase correction voltage is generated based on a phase correction voltage lookup table. Herein, the lookup table calibration apparatus can be configured to concurrently populate and/or calibrate the modulated voltage lookup table and the phase correction voltage lookup table based on a measured gain and a measured phase of the RF signal, respectively.
1. A lookup table calibration apparatus comprising:
a power amplifier circuit comprising:
a phase shifter circuit configured to phase-shift a radio frequency (RF) signal based on a modulated phase correction voltage generated based on a phase correction voltage lookup table comprising a plurality of power indexes each correlating a respective power level of the RF signal with a respective one of a plurality of phase correction voltage targets; and
a power amplifier configured to amplify the phase-shifted RF signal based on a modulated voltage generated based on a modulated voltage lookup table comprising the plurality of power indexes each correlating the respective power level of the RF signal with a respective one of a plurality of modulated voltage targets; and
a calibration control circuit configured to, for each of the plurality of power indexes:
adjust the modulated voltage until a measured gain of the amplified RF signal equals a reference gain;
update the respective one of the plurality of modulated voltage targets in the modulated voltage lookup table based on the adjusted modulated voltage;
adjust the modulated phase correction voltage until a measured phase of the amplified RF signal equals a reference phase; and
update the respective one of the plurality of phase correction voltage targets in the phase correction voltage lookup table based on the adjusted modulated phase correction voltage.
2. The lookup table calibration apparatus of claim 1 , wherein, for each of the plurality of power indexes, the calibration control circuit is further configured to generate the RF signal at the respective power level and provide the RF signal to the power amplifier circuit.
3. The lookup table calibration apparatus of claim 1 , further comprising a measurement circuit coupled to an output of the power amplifier circuit and configured to generate the measured gain and the measured phase of the amplified RF signal.
4. The lookup table calibration apparatus of claim 1 , further comprising a storage circuit configured to store the reference gain and the reference phase.
5. The lookup table calibration apparatus of claim 4 , wherein the calibration control circuit is further configured to:
determine the reference gain and the reference phase of the RF signal; and
store the reference gain and the reference phase in the storage circuit.
6. The lookup table calibration apparatus of claim 1 , wherein the calibration control circuit is further configured to:
determine whether the measured gain is equal to the reference gain after adjusting the modulated phase correction voltage to cause the measured phase to equal the reference phase; and
in response to determining that the measured gain is different from the reference gain:
re-adjust the modulated voltage until the measured gain of the amplified RF signal equals the reference gain; and
update the respective one of the plurality of modulated voltage targets in the modulated voltage lookup table based on the re-adjusted modulated voltage.
7. The lookup table calibration apparatus of claim 1 , wherein the modulated voltage lookup table and the phase correction voltage lookup table are both provided in an envelope tracking integrated circuit (ETIC) configured to generate the modulated voltage and the modulated phase correction voltage.
8. A method for performing lookup table calibration comprising:
receiving a measured gain and a measured phase of a radio frequency (RF) signal for each of a plurality of power indexes;
adjusting a modulated voltage until the measured gain equals a reference gain;
updating a respective one of a plurality of modulated voltage targets in a modulated voltage lookup table based on the adjusted modulated voltage;
adjusting a modulated phase correction voltage until the measured phase equals a reference phase; and
updating a respective one of a plurality of phase correction voltage targets in a phase correction voltage lookup table based on the adjusted modulated phase correction voltage.
9. The method of claim 8 , further comprising, for each of the plurality of power indexes, generating the RF signal at the respective power level.
10. The method of claim 8 , further comprising measuring the RF signal at an output of a power amplifier circuit to generate the measured gain and the measured phase.
11. The method of claim 8 , further comprising:
determining the reference gain and the reference phase of the RF signal; and
storing the determined reference gain and the determined reference phase in a storage circuit.
12. The method of claim 8 , further comprising:
determining whether the measured gain is equal to the reference gain after adjusting the modulated phase correction voltage to cause the measured phase to equal the reference phase; and
in response to determining that the measured gain is different from the reference gain:
re-adjusting the modulated voltage until the measured gain of the amplified RF signal equals the reference gain; and
updating the respective one of the plurality of modulated voltage targets in the modulated voltage lookup table based on the re-adjusted modulated voltage.