ycle, as opposed to the peaks, by dynamically adjusting the supply voltage to the PA. The effect of OFDM-based signals on PAPR motivated the use of ET technique to achieve considerable energy saving in high-PAPR transmitters. More commercial ET PAs have been developed for 4G/5G UE transmitters. High voltage supply: With higher supply voltage, the portion of knee voltage of the transistors can be minimized, which means the PA will achieve higher efficiency. Another advantage of high supply voltage is that the load line can be increased. New Radio Access RF and Transceiver Design Considerations With increasing of the load line, the associated loss will be lower, which further improves the efficiency. However, because the supply voltage of the handset is 3.8 V at nominal condition, another DC-DC converter is needed to achieve a higher voltage. It should be noted that the DC-DC's efficiency is always less than 100%. Power combination techniques: The PAs often need to support very large output power; therefore power combination techniques are used to combine the outputs of small-PAs. Since the combiners are always at the last stage of the power amplification, the efficiency of the combiners will affect the overall PA efficiency. There are many power combination techniques including voltage or current combination. However, regardless of the combina- tion technique used, low-loss, high-Q components must be utilized. Among combination techniques the push-pull combiner has the advantage of doubling the impedance which as to be matched, lowering the loss of the impedance transformation. Doherty amplifier: The Doherty amplifier uses a configuration known as active load-pull technique, which can modify the RF load of the PA in different RF power levels. Thus when the power backs off from the peak power, the efficiency will not drop significantly comparing to the traditional PA topologies. Each Doherty amplifier includes two devices, which are referred to as the main and the auxiliary devices, where the RF output power is the