Journal of the Korea Institute of Information and Communication Engineering (한국정보통신학회논문지)

The Korea Institute of Information and Commucation Engineering (한국정보통신학회)
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Differential 2.4-GHz CMOS Power Amplifier Using an Asymmetric Differential Inductor to Improve Linearity

비대칭 차동 인덕터를 이용한 2.4-GHz 선형 CMOS 전력 증폭기

  • Jang, Seongjin (School of Electronic Engineering, Soongsil University) ;
  • Lee, Changhyun (School of Electronic Engineering, Soongsil University) ;
  • Park, Changkun (School of Electronic Engineering, Soongsil University)
  • Received : 2019.05.18
  • Accepted : 2019.05.22
  • Published : 2019.06.30
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Abstract

In this study, we proposed an asymmetric differential inductor to improve the linearity of differential power amplifiers. Considering the phase error between differential signals of the differential amplifier, the location of the center tap of the differential inductor was modified to minimize the error. As a result, the center tap was positioned asymmetrically inside the differential inductor. With the asymmetric differential inductor, the AM-to-AM and AM-to-PM distortions of the amplifier were suppressed. To confirm the feasibility of the inductor, we designed a 2.4 GHz differential CMOS PA for IEEE 802.11n WLAN applications with a 64-quadrature amplitude modulation (QAM), 9.6 dB peak-to-average power ratio (PAPR), and a bandwidth of 20 MHz. The designed power amplifier was fabricated using the 180-nm RF CMOS process. The measured maximum linear output power was 17 dBm, whereas EVM was 5%.

본 연구에서는 차동 구조의 고주파 증폭기를 위한 비대칭 차동 인덕터를 제안하였다. 제안 된 비대칭 차동 인덕터는 증폭기 내 차동 신호 간 위상 오차를 완화하기 위한 것으로서, 차동 인덕터에 형성되는 Center-tap의 위치를 조정하여, 전력 증폭기를 구성하는 구동 증폭기의 차동 신호에서 바라보이는 임피던스가 동일하게 형성 되도록 하였다. 이를 통하여 기존 차동 인덕터를 사용하는 경우 대비 AM-to-AM 및 AM-to-PM 왜곡이 완화됨을 확인 하였다. 제안하는 비대칭 차동 인덕터의 효용성을 확인하기 위하여 180-nm RFCMOS 공정을 이용하여 2.4-GHz CMOS 전력 증폭기를 설계하였으며, EVM 5% 기준 20 dB의 전력 이득과 17 dBm의 최대 선형 출력 전력을 얻었다.

Keywords

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Fig. 1 Layout of the driver stage inductor: (a) symmetric and (b) asymmetric layouts.

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Fig. 2 Proposed asymmetric differential inductor.

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Fig. 3 Proposed asymmetric differential inductor.

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Fig. 4 Phase difference for typical and proposed differential inductors.

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Fig. 5 Distortions based on input power: (a) AM-to-AM and (b) AM-to-PM distortions.

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Fig. 6 Chip photograph of the designed power amplifier.

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Fig. 7 Measured gain, EVM, and PAE based on ouptut power.

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Fig. 8 Measured spectrum mask at the EVM of 3.98%.

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