Method of in-device phase measurement and correlation to programmable factors
View Patent ↗A method is provided for calibrating Amplitude Modulation to Phase Modulation (AM/PM) predistortion coefficients for a polynomial used to compensate for AM/PM distortion of a power amplifier in the transmit chain of a mobile terminal. In general, the power amplifier is controlled by a variable supply voltage, which is generated based on an adjustable power control signal. After the power amplifier is placed in the mobile terminal, a predetermined data pattern is transmitted in a transmit burst. During the transmit burst, the variable supply voltage is changed from a first value to a second value, and a resultant phase shift in the radio frequency output signal provided by the mobile terminal is measured. Based on the phase shift, one of numerous predetermined sets of AM/PM predistortion coefficients is selected as the AM/PM coefficients for the mobile terminal.
1. A method for calibrating Amplitude Modulation to Phase Modulation (AM/PM) predistortion of a transmitter of a mobile terminal comprising:
transmitting a predetermined data pattern in a transmit burst to provide an output signal;
changing a variable supply voltage controlling an output power of power amplifier circuitry of the transmitter from a first value to a second value during the transmit burst;
measuring a phase shift caused by changing the variable supply voltage to the second value, wherein the phase shift is a phase shift between a phase of the output signal before changing the variable supply voltage to the second value and a phase of the output signal after changing the variable supply voltage to the second value; and
selecting one of a plurality of predetermined sets of AM/PM predistortion coefficients as AM/PM predistortion coefficients defining the AM/PM predistortion of the transmitter of the mobile terminal based on the phase shift.
2. The method of claim 1 wherein the predetermined data pattern includes a training sequence defining a center of the transmit burst, and measuring the phase shift comprises synchronizing external test equipment to the training sequence.
3. The method of claim 2 wherein the predetermined data pattern is all zeros except for the training sequence.
4. The method of claim 2 wherein changing the variable supply voltage from the first value to the second value comprises changing the variable supply voltage from the first value to the second value at a predetermined time between the beginning of the transmit burst and the training sequence.
5. The method of claim 2 wherein changing the variable supply voltage from the first value to the second value comprises changing the variable supply voltage from the first value to the second value at a predetermined time after the training sequence and before the end of the transmit burst.
6. The method of claim 1 further comprising providing the variable supply voltage based on an adjustable power control signal and providing the adjustable power control signal based at least in part on a power amplifier gain setting, wherein changing the variable supply voltage from the first value to the second value comprises changing the power amplifier gain setting from a first power amplifier gain setting to a second power amplifier gain setting such that the adjustable power control signal is provided to change the variable supply voltage from the first value to the second value.
7. The method of claim 1 further comprising providing the variable supply voltage based on an adjustable power control signal, wherein changing the variable supply voltage from the first value to the second value comprises:
providing the adjustable power control signal such that the variable supply voltage is set to the first value prior to the beginning of the transmit burst; and
increasing the adjustable power control signal after a predetermined delay from the beginning of the transmit burst such that the variable supply voltage is ramped up from the first value to the second value during the transmit burst.
8. The method of claim 1 further comprising providing the variable supply voltage based on an adjustable power control signal, wherein changing the variable supply voltage from the first value to the second value comprises:
delaying ramp-up for the transmit burst a predetermined time from the beginning of the transmit burst such that ramp-up occurs during the transmit burst; and
increasing the adjustable power control signal to effectuate ramp-up after the predetermined time from the beginning of the transmit burst such that the variable supply voltage increases from the first value to the second value.
9. The method of claim 1 wherein the first value of the variable supply voltage is 0.45 V and the second value of the variable supply voltage is 1 V.
10. The method of claim 1 wherein setting the variable supply voltage to the first value, changing the variable supply voltage to the second value, measuring the phase shift, and selecting one of the plurality of predetermined sets of AM/PM predistortion coefficients each occur after the power amplifier circuitry is placed into the mobile terminal.
11. The method of claim 1 further comprising:
measuring the phase shift caused by changing the variable supply voltage to the second value for each of a plurality of power amplifier circuitries;
dividing the plurality of power amplifier circuitries into a number of groups based on the phase shift; and
determining the plurality of predetermined sets of the AM/PM predistortion coefficients by determining one of the plurality of predetermined sets of AM/PM predistortion coefficients for each of the number of groups of the plurality of power amplifier circuitries.