Design techniques for broadband linear power amplifiers.

摘要

In this dissertation, several crucial aspects concerning power amplifiers' performances on thermal management, linearity and bandwidth are discussed. We proposed and explored a novel ballast resistor network to alleviate the thermal issue exists in power amplifier cells. It shows that the novel network can achieve a more uniform temperature distribution than the conventional one. A power amplifier's linearity is improved by about 3dB using our programmable predistortion linearizer implemented as input stage. Then we discuss that RLC high frequency loss compensation network works as a bandwidth enhancement technique not only at small-signal but also at large signal condition. The RLC network is utilized on a cascode amplifier, saving design efforts for an extra linearizer stage. Explanation is given regarding why RLC can improve bandwidth and linearity. Volterra series method is used to demonstrate the RLC effects on nonlinear condition.;Combining those previously discussed techniques, a broadband WiMAX linear power amplifier is designed. Some previous work used different power amplifier in one module to cover different WiMAX band with bias circuit toggling on and off. In contrast to it, the highlight of our design is that one power amplifier with one input/output matching networks shall be able to cover currently existing WiMAX bands from 2.5GHz to 5.8GHz. The power amplifier is composed of two cascode stages. The die size is 1.8mmx1.4mm. The gain is 29dB, output power is 30 dBm and PAE is 21% at P1dB. EVM is about 5% at output power level of 25dBm at 3.6GHz.;To the best of our knowledge, this is the first time to use RLC network in a power amplifier design to improve bandwidth and linearity. Also, the broadband WiMAX linear power amplifier is a first demonstration to cover all three existing WiMAX bands in one power amplifier design.