The RF power amplifier is required to be linear to maintain signal integrity with limited spectral regrowth in the mobile radio transmitter with digital modulation format. To maintain the linearity of an RF amplifier, a Class-A or Class-AB mode amplifier is typically operated.
In many wireless systems, the power transmitted by the mobile unit is adjusted such that signals arriving at a base station from all portable transmitters are similar in power level. Because of having to accommodate the variable distance between mobile and base units, as well as multipath and shadow fading, the amplifiers operate over a wide dynamic power range extending from a maximum level to 10dB in power back-off.
Envelope tracking(ET) amplifier with variable bias voltage is a certain method for power amplifier application of the third generation cellular phones.
However, the input and output impedance of transistors vary with the changing of the Q-point and power level. Because of the variation of impedance, the gain and efficiency of ET amplifiers decreases a lot and the VSWR and stability become worse. The mismatching of dynamic ET amplifier can't be substantially avoided.
In this thesis, the mismatching of dynamic ET amplifiers is proven to be compensated using a varactor diode.
The gain is experimentally improved by 7㏈ above 15㏈m output power. The efficiency improve about 2.5 times. The DC power consumption ET amplifier of which the impedance is compensated is 37% of bias fixed power amplifier