基于Sweet Spot的线性高效率功率放大器设计

摘要

该文通过IMD Sweet Spot解决高效功率放大器的线性问题，使功率放大器在保证一定线性指标时还保持了高效率。IMD Sweet Spot是由受偏置电压影响的小信号失真(弱非线性)和由器件的开启及饱和特性所决定的大信号失真(强非线性)相互作用的结果。通过改变偏置电压可以控制其弱非线性，从而控制IMD Sweet Spot的产生。寻求合适的偏置电压使得IMD Sweet Spot在增益开始压缩时产生，功率放大器可以有较高的效率，且线性较好。基于该原理设计的线性高效功放测试结果表明，在中心频率2.2 GHz处输出功率为37.1 dBm时，三阶交调失真分量(IMD3)和五阶交调失真分量(IMD5)均小于−30 dBc，此时漏极效率达到53.4%。%This paper utilizes intermodulation distortion (IMD) sweet spot effect to solve the linear problem of high-efficient power amplifier (PA), so that PA can maintain high levels of both efficiency and linearity. IMD sweet spot is the result of interactions between circuit's small-signal nonlinear distortion (weak nonlinearity) determined by the PA quiescent operating point and large-signal distortion effects determined by the device current turn-on and current saturation (strong nonlinearity). The weak nonlinearity can be controlled by changing the gate bias. By seeking appropriate bias voltage for IMD sweet spot generated at the beginning of the transistor gain compression, PA can achieve high efficiency and good linearity. Based on the effect of sweet spot, a high-efficiency linear PA has been designed. Test results show that at center frequency of 2.2 GHz, 37.1 dBm output powers, 53.4%drain efficiency can be obtained, while the third-order intermodulation distortion (IMD3) and the fifth-order intermodulation distortion (IMD5) are less than−30 dBc.