Methods for tuning and controlling output power in polar transmitters
View Patent ↗A power tuning method determines values of a magnitude control signal that controls the magnitude of an amplitude-modulated power supply signal applied to a power supply port of a power amplifier of a polar transmitter and an amplitude control signal that controls the amplitude of a constant-envelope phase-modulated signal applied to a radio frequency input port of the power amplifier necessary to set the output power of the polar transmitter to a target output power. The method is repeated and performed for a plurality of different target output powers. Output-power-level dependent power control parameters calculated from the applied method are used to set the values of the magnitude control and amplitude control signals during normal operation. Using the output-power-level dependent power control parameters, the magnitude control and amplitude control signals are changed in a continuous manner with changes in output power and over the full dynamic range of output powers the polar transmitter can be commanded to operate, thereby obviating any need for a closed-loop power detection mechanism to correct for power discontinuities.
1. A power tuning method that is applied to a power amplifier (PA) prior to normal operation, comprising:
a) applying a magnitude control signal to a magnitude control input of an amplitude modulator configured to control a magnitude of an amplitude-modulated power supply signal applied to a power supply port of the PA;
b) applying an amplitude control signal to an amplitude control input of an amplitude control circuit configured to control an input power of a constant-envelope phase-modulated carrier signal applied to a signal input of the PA;
c) setting the input power of the constant-envelope phase-modulated carrier signal to a predefined value determined by a function characterizing input-output power characteristics of the PA;
d) measuring an actual output power of an output signal at a signal output of the PA;
e) determining whether the actual output power is within a desired precision of a target output power;
f) modifying the magnitude control signal, if it is determined that the actual output power is not within the desired precision of the target output power, by one of increasing the magnitude control signal if the actual output power is lower than the target output power and reducing the magnitude control signal if the actual output power is higher than the target output power;
g) determining whether the magnitude control signal has been reduced to a minimum allowable value and if the value of the magnitude control signal has been reduced to the minimum allowable value, reducing the input power of the constant-envelope phase-modulated carrier signal, instead of reducing the magnitude control signal below the minimum allowable value;
h) repeating steps d) through g) until the actual output power is within the desired precision of the target output power; and
j) calculating polynomial coefficients from the values of the magnitude control signal and input power after it is determined that the actual output power is within the desired precision of the target output power.
2. The power tuning method of claim 1 , further comprising calculating first and second power control parameters from the values of the magnitude control signal and input power after it is determined that the actual output power is within the desired precision of the target output power.
3. The power tuning method of claim 2 , further comprising repeating steps c) through h) for a plurality of different target output powers, said plurality of different target output powers determined based on the input-output power characteristics of the PA.
4. The power tuning method of claim 3 , further comprising arranging first and second power control parameters calculated for each target output power of said plurality of different target output powers in a look up table (LUT).
5. The power tuning method of claim 4 , further comprising storing said LUT in a nonvolatile memory.
6. The power tuning method of claim 4 wherein said LUT comprises a plurality of entries, each entry corresponding to one of the target output powers of said plurality of different target output powers, and each entry including associated first and second power control parameters.