Traditional High Efficiency Power Amplifiers are often very efficient while operating at full power, such as those using the Envelope Elimination and Restoration (EER) method of linearization a non-linear power amplifier through high-level modulators. However, the efficiency of the EER methods undesirably drops as the power level decreases (e.g., power back-off) stressing the envelope amplifier through recreation of the original signal. Similarly, linearization methods employing Linear Application using Non-linear Components (LINC) transmitters suffer degraded efficiency at power levels backed off from peak as they use an inefficient RF dump resistor in their output combiner.
In addition, when these amplifiers are operated with wideband waveforms having high peak-to-average ratios, such as Quadrature Amplitude Modulation (QAM), Wideband Code Division Multiple Access (WCDMA), or Orthogonal Frequency Division Multiplexing (OFDM), the net efficiency is considerably less than the efficiency at high power levels. Since the average power is often 6-10 dB below peak levels, these traditional methods suffer a degraded efficiency during average use. Further, high-level modulators limit the modulation bandwidth of the wideband waveforms as they struggle to follow the widely varying signal envelopes.
Consequently, a need remains for an efficient alternative operable at average power levels backed off from peak power to overcome the shortcomings of traditional inefficient high power amplifiers.