| Power amplifier is an important part in communication systems. About 30% of operation charge of telecom operators is spent on electricity, 50%~60% of which is consumed by base station. And within base station, power amplifier consumed the most. Low efficiencient power amplifier means more cost on energy consumption. Meanwhile most of electric power is transformed into heat energy, so this increases equipment maintance cost and decreases equipments longevity.From the viewpoint of environmental protection, it is estimated that in 2009 carbon dioxide emission is about 7.5 ton around the world. In China, 3G network is developing, so advanced energy saving base station is necessary for green 3G network construction. This is also the requirements for building a conservation-oriented society and fulfilling energy saving as well as emission reduction. Increasing the efficiency of power amplifier is the key to implement energy saving base station.Power amplifier is nonlinear component. The efficiency is low if we adopt simple power back-off to make power amplifier work in linear aera. Nine-carrier TD-SCDMA signal with PAPR at approximately 12dB, power amplifier efficiency will lower than 10% as the result of signal power after back-off to 12dB.At present, digital signal processing is the method conserving both high efficiency of power amplifier and linearity. This paper puts emphasis on the research and implementation of key technologies in high efficiency power amplifier.PAPR could improve power amplifier output power while the PA is working in the same linear district. To maintain the linearity of power amplifer output, back-off power equals the difference between the power of linearity working zone and the sum of PAPR and saturation power. The lower the output PAPR is, the less the back-off power is, so the more efficienct the power amplifier will be.DPD could expand PA working linearity zone. When PA output power is increasing to non-linear zone, PA output signal will deviate from ideal linear curve which leads to signal quality decreasing and adjacent channel interference. DPD could compare the distorted signal and reference signal, then pre-distort the input datas with opposite distortion performance to power amplifier and eliminate the ultimate distortion. PA with expanded linear zone is able to output higher power level, thus has higher efficiency.First, this paper will introduce equivalent baseband model of power amplifier distortion, including amplifier AM-AM distortion and AM-PM distortion,and the affects to power amplifier distortion caused by memory effection. Later, will present the architecture of high efficient power amplifier, and describe the position as well as fuction.Furthermore, this paper presents the research on two key techniques in high efficiency power amplifier, they are CFR and DPD. And implement base band signal processing according to pulse cancellation CFR technique and memory polynomial DPD.Finally, we test base band signal processing by exterior connecting Doherty using six-carrier TD-SCDMA composite signal. Under the same linearity requirement, we promote power amplifier efficiency from 6% to 37.7%.The above results validate the engineering feasibility of digital assistance function of broadband high efficiency power amplifier. It has some reference meanings to the large-scale application of power amplifier in mobile communications. It also has some economical value. |
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