A power amplifier tends to dissipate significant amounts of power. This is particularly true for linear power amplifiers such as those used to process orthogonal frequency-division multiplexing (OFDM) signals including both phase and amplitude information. Linearization techniques can be used to improve the linearity and efficiency of a power amplifier. As one example, a popular linearization technique uses digital predistortion to correct the amplitude and phase distortion that occurs in the power amplifier.
A common problem with known linearization techniques is determining how to make them track (i.e., adjust, or account for) variations in fabrication, temperature, environmental influences, aging, and other factors. To overcome this problem, a calibration scheme has been employed that adjusts the linearization settings to the current state of the power amplifier. In one exemplary scheme, the output signal of the power amplifier is “looped-back” through the receiver section of the overall circuitry and analyzed using digital signal processing techniques, so that calibration of the power amplifier might be performed.
However, this approach often suffers from being too sensitive to incidental and/or unintentional coupling between the input and/or output of power amplifier signals, and the signals of the receiver input circuitry. In another case, non-linearities of a functional block or blocks other than the power amplifier can disrupt or alter the looped-back signal content. As a result of any or all of these disturbances, the digital signal processing and/or other calibration means can exert an erroneous calibration effect on the power amplifier linearization adjustment.