High Efficiency WCDMA Power Amplifier With Pulsed Load Modulation (PLM)

Complex non-constant-envelope modulations are often used in wireless communications. A power amplifier (PA) is developed based on the concept of pulsed load modulation (PLM) that can enhance the power efficiency of the PA when the output power is back off from the peak due to modulations. The PLM technique utilizes the time-varying behavior of switched resonators to form an optimal, power dependent load impedance. The switched resonator consists of a balanced pair of switching mode PAs that drive a high-Q bandpass filter. In addition to its efficiency enhancement through PLM, the PA is able to preserve the linearity of complex modulations through the architecture of envelope delta-sigma modulation (EDSM). In this paper, a 1.87 GHz PLM power amplifier is fabricated with a pair of 0.35 μm GaAs pHEMT devices. The duty cycle tests show its significant improvement on power efficiency at different back-off levels over traditional Class-B amplifiers. The PA module is also tested with a single-channel WCDMA signal with peak to average ratio (PAR) of 10.8 dB. It has achieved 39 dBc adjacent channel leakage ratio (ACLR) at 5 MHz offsets without needing additional linearization techniques. The power added efficiency in this case is 43% including the loss of the output filter and 52.6% if the loss of the filter is de-embedded.

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