| In modern wireless communication system, power amplifier (PA) is of great importance as the output stage. To enhance the efficiency, the PAs always work at Class AB, Class B or above. Nowadays, the spectrum is expensive, the new technologies demand maximum amount of data with minimum spectrum usage in transmission. This requires complicated modulation techniques, which lead to non-constant envelops of input signals and increase of their peak-to-average ratio. During that time, the large signal causes deep nonlinearity, which greatly affects the system performance.This thesis aims the design of 10W high linearity H.F PA. With the transmission line transformer (TLT) matching network and parallel feedback of the transistor, the output power flatness will be confined to±0.5dB.This subject uses the classical feedback structure: Cartesian Loop to realize high linearity. The 3rd inter-modulation distortion (IMD3) in Two-Tone test increases 15dB at least.Based on the need of circuit design, first of all, this thesis covers the design method of PA and its nonlinearity theories. Different types of matching network are recommended, especially the TLT matching model and its characteristics. And then it talks about Cartesian Loop and the design theory of its components. This subject mainly talks about the components for the H.F use, emphasizing on the theory and circuit design of TLT, transmission line coupler (TLC), High-pass / Low-pass filter phase shifter, etc. To guarantee the stability, the circuit uses variable phase shifter to compensate the delay in Cartesian Loop, avoiding self-oscillation. At last, it discusses the debugging process, ultimate test result and some suggestions for further improving. |
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