OUTPHASING TRANSMITTER An Outphasing Transmitter Using Class - E PAs and Asym - metric Combining : Part

H igh efficiency linear amplification is of great interest in modern communication systems as it increases talk time, decreases power consumption , decreases heat dissipation, and improves reliability. The efficiency of linear power amplifiers (PAs) is highest at the peak output power (PEP) and decreases significantly for low amplitudes, as shown in Figure 1. Signals with time-varying amplitudes (amplitude modulation) therefore produce time-varying efficiencies, the probability density function (pdf) of the envelope is a means of how much time an envelope spends in certain amplitude level, as shown in Figure 2. Hence, obtaining a high average efficiency [1] therefore requires a combination of amplifier and architecture that improves efficiency at low as well as high amplitudes. It is achieved by combining high-efficiency power amplifier and a transmitter architecture such as envelope elimination, Doherty, or outphasing [1]. An outphasing transmitter (Figure 3) produces a variable-amplitude output by varying the phases of the driving signals to its RF-power amplifiers. The phase modulation causes the instantaneous vector sum of outputs of the two PAs to follow the desired signal amplitude. In a microwave implementation, power combiners based upon transmission lines are typical. The outphasing transmitter, also known as linear amplification using non-linear components (LINC) was originally developed to provide linear amplification with active devices that have poor linearity [1, 2]. H. Chireix added complementary shunt reactances at the inputs of the combiner to improve the efficiency over a range of amplitudes (Fig. 3).