This paper presents a power amplifier (PA) topology to improve the back-off efficiency and the linearity of millimeter-wave (mm-wave) PAs without area overhead. In this paper, an asymmetrical series power combiner with LC tuning circuits is proposed to mimic the Doherty operation. Due to high back-off efficiency and high linearity behavior, the proposed Doherty topology well suits for E-band communication applications. Two transformer-based E-band PAs are designed and measured to demonstrate the proposed mm-wave Doherty concept. The first implementation achieves 16.2-dBm output power with a of 15.2 dBm using a 0.9-V supply. The second implementation demonstrates 21-dBm output power with a power-added efficiency (PAE) of 13.6% at a 1.5-V supply. The PAE at 6-dB power back-off is still as high as 7%.Index Terms-Back-off efficiency, CMOS, Doherty power amplifier (PA), millimeter-wave (mm-wave) backhaul.
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 high back-off efficiency with good linearity. In addition, the PA has two power modes to further reduce the power consumption when low output power is required. The PA combines four push-pull amplifiers by using an symmetrical hybrid transformer that ensures 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 addition, 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.
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