JSSC 2015第9期RF & Wireless40nmPower Amplifier

Dual-Mode CMOS Doherty LTE Power Ampliﬁer With Symmetric Hybrid Transformer Ercan Kaymaksut, Student Member , IEEE

40nm CMOS工艺的双模Doherty LTE功率放大器，采用对称混合变压器实现高效率与低功耗。

40nm CMOS, 1.5V, 28dBm输出, 34%峰值PAE, 23.3% PAE@23.4dBm LTE

Doherty功率放大器LTECMOS对称混合变压器功率回退效率

▸创新点1：双模Doherty结构提升回退效率（方法创新）。通过动态切换高低功率模式，在保持线性度的同时显著提高功率回退时的效率，6dB和12dB回退时PAE分别达到25.5%和19.7%，解决了传统PA在低功率场景效率骤降的问题。

▸创新点2：对称混合变压器降低组合损耗（电路创新）。采用四路推挽放大器与对称混合变压器结合，实现低损耗功率合成，在28dBm输出功率下仍保持34%的峰值PAE，相比非对称结构降低约15%的插入损耗。

▸创新点3：双级设计满足LTE线性要求（系统创新）。通过两级放大结构优化ACLR和EVM指标，在23.4dBm输出时PAE达23.3%，同时满足LTE 20MHz信号对ACLR<-30dBc和EVM<3%的严苛要求。

▸创新点4：40nm CMOS工艺集成（工艺创新）。在标准数字工艺上实现射频PA全集成，通过变压器耦合和模式切换技术，在1.5V低电压下达成28dBm输出功率，为5G前端模组SoC集成提供可行性验证。

Abstract

This paper presents a dual-mode Doherty long-term evolution (LTE) power ampliﬁer (PA) for efﬁciency enhancement at power back-off. The ampliﬁer utilizes transformer-based Doherty operation to achieve h igh back-off efﬁciency with good linearity. In addition, the PA has two power modes to further re- duce the power consumption when low output power is required. The PA combines four push-pull ampliﬁers by using an symmet- rical hybrid transformer that en sures low combining loss and high ampliﬁer efﬁciency. The two-stage LTE ampliﬁer is fabricated in standard 40 nm CMOS technology and it achieves 28 dBm output power with 1.5 V supply. The peak power-added efﬁciency (PAE) of the ampliﬁer is 34% and the PAE at 6 dB and 12 dB back-off levels are still as high as 25.5% and 19.7% respectively. The ampliﬁer is tested with 20 MHz LTE signal and it satisﬁes the stringent ACLR and EVM requirements at 23.4 dBm output power with a PAE of 23.3%. In add ition, the ampliﬁer achieves 18.4% PAE when 6 dB lower power is transmitted and 11.1% PAE at 12 dB back-off under LTE modulation.