Gan Doherty, Power Amplifier Design And Modeling

The power amplifiers (PA) are the most power-consuming block in wireless communication systems. With the development of wireless communication technology, the performances of PA should to be better and better. In the modern wireless communication systems, spectrum is expensive, and complicated modulation techniques are required to transmit maximum amount of data with minimum spectrum usage. These newer modulation techniques lead to wide, dynamic signals that require linear PA. Although linear PA is achievable, it always comes at the expense of efficiency. Most of the modern wireless applications such as TD-SCDMA, WCDMA, CDMA use non-constant envelope modulation techniques with a high peak to average ratio. In order to satisfy the demand of linearity, PA implemented in such applications are forced to operate at a backed off region from saturation. However, power added efficiency (PAE) is sacrificed while power is back off. Therefore, in order to prolong the battery lifetime of communication systems, the research of PA with demanded linearity and higher efficiency is very important. In this thesis, the Doherty technique can maintain the high efficiency for a wider backed off region from saturation.A 10W S band Doherty PA (DPA) is introduced and a simple model is given in this thesis. This DPA shows a 16.4% increase in PAE at 6dB back off from saturation, and maintains PAE upon 59% between transitional point and peak point, compared to the traditional balanced class AB PA. In this thesis, infection of peak PA's bias grid voltage to PAE, gain and linearity is analyzed, in order to improve the linearity of DPA at large output power, adaptive bias is put forward. At the same time, infection of GaN transistor's temperature to PAE, gain and linearity is also analyzed. Moreover, a simple model of DPA using radial-basis function neural network is presented.