基于双向牵引与谐波抑制的Doherty功率放大器设计

为了提高功率放大器(Power Amplifier,PA)的效率,提出一种基于双向牵引与谐波抑制的对称式Doherty功率放大器(Symmetrical Doherty Power Amplifier,SDPA)结构。该结构在经典DPA 的基础上,首先利用多谐波双向牵引技术获得功放的实际最佳阻抗,然后对主辅功放的二、三次谐波进行抑制,降低了漏极电压电流的重合,最后通过添加补偿线调节主辅功放的功率分配,使得功放整体获得最大的效率。为了验证上述谐波抑制理论与双向牵引技术的正确性,采用GaN 器件设计了一款应用在4G 基站的SDPA。测试结果显示:SDPA 在2.6 GHz 处的小信号增益为12.6 dB,2.5-2.7 GHz 频段内的增益平坦度为±0.75 dB,频带内的S11小于-11.9 dB,在三载波测试时经过数字预失真(Digital Pre-Distortion,DPD)系统纠正后的相邻信道泄漏比(Adjacent Channel Leakage Rate,ACLR)约为-45 dBc,SDPA 在峰值功率点附近的功率附加效率(Power Added Efficiency,PAE)接近60%,在回退点处的PAE约为48%。实验结果验证了该设计方案的可行性。

Design of Doherty Power Amplifier Based on Bidirectional Traction and Harmonic Suppression

In order to improve the efficiency of power amplifier(PA), a symmetric Doherty power amplifier (SDPA) based on bidirectional traction and harmonic suppression is proposed. On the basis of the classic DPA, the structure first uses the multi-harmonic bidirectional traction technology to obtain the actual optimum impedance of the power amplifier. Then the two and three harmonic of the main and auxiliary power amplifier are suppressed, and the coincidence of the leakage voltage and current is reduced. Finally, the power distribution of the main and auxiliary power amplifiers is adjusted by adding compensation lines, so that the amplifier can get the maximum efficiency. In order to verify the correctness of the harmonic suppression theory and the bidirectional traction technology, a SDPA device applied to 4G base station is designed by using GaN device. The test results show that the small signal gain of SDPA at 2.6 GHz is 12.6 dB, the gain flatness within the 2.5-2.7 GHz band is ±0.75 dB, and the S11 in the frequency band is less than -11. 9 dB. After the digital predistortion (DPD) system is corrected, the adjacent channel leakage rate (ACLR) at the three carrier test is about -45 dBc, the power additional efficiency (PAE) near the peak power point of SDPA is close to 60%, and the PAE at the backdrop point is about 48%. The experimental results verify the feasibility of the design.