Radio-frequency (RF) power amplifiers (PA) have a nearly linear response only at small input amplitudes, with their outputs gradually saturating as input amplitudes increase. This slightly sub-linear transfer characteristic gives rise to out-of-band emissions, which can potentially interfere with other users of the RF spectrum. Regulatory requirements place limits on the maximum out-of-band emissions by a device. In turn, these translate to operating the PA at a highly linear region, e.g., at low input amplitudes compared to the dynamic range of the PA. However, low input amplitudes are associated with low PA efficiencies. This disclosure describes techniques to adapt the operating point of the PA to suit the targeted output power and/or bandwidth. By doing so, the emissions mask is met even as the PA operates at its worst conditions, and energy efficiencies are achieved when the device is operating at its most efficient conditions. The techniques reduce current drain and heat dissipation, and improve battery life.
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Sun, Ming; He, Fei; and Kincaid, Mike, "Adaptive Biasing Of Radio-Frequency Power Amplifiers", Technical Disclosure Commons, (October 24, 2019)