A Wideband Supply Modulator for 20 MHz RF Bandwidth Polar PAs in 65 nm CMOS

• Published in: IEEE journal of solid-state circuits Vol. 44; no. 4; pp. 1272 - 1280
• Main Authors: Shrestha, R., van der Zee, R., de Graauw, A., Nauta, B.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01-04-2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplifiers; Applied sciences; Bandwidth; Broadband amplifiers; Cascoded nested Miller; Chirp modulation; Circuit properties; CMOS; Design. Technologies. Operation analysis. Testing; Efficiency; Electric, optical and optoelectronic circuits; Electronic circuits; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Exact sciences and technology; Integrated circuits; Linearity; Modulators; Noise levels; polar transmitters; power amplifier; Power generation; Radio frequencies; Radio frequency; Radiofrequency amplifiers; RF signals; Ripples; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Signal convertors; Signal generators; supply modulator; Switching; Wideband; Performance evaluation; Wireless LAN; Modulator; Output power; supply modulator; Small signal behavior; Linear amplification; Transmitter; Power electronics; Switching; Optimal design; CMOS; Cascoded nested Miller; RF; Complementary MOS technology; polar transmitters; Class AB; Radiofrequency amplifiers; Power amplifier
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2009.2014730

Polar modulated RF amplifiers have the potential to enhance efficiency while achieving sufficient linearity for a signal having non-constant envelope. However, switching modulators used in such architectures to generate the envelope signal are difficult to implement because of the high bandwidth and low switching ripple requirement, while achieving high efficiency even at large power back-off. This paper presents a wideband supply modulator for a 20 MHz RF bandwidth polar modulated PA. Realized in 65 nm CMOS, it consists of a cascoded nested Miller compensated linear amplifier and a class D switching amplifier. The class-AB linear amplifier with cascoded Miller compensation in the modulator reduces the output switching ripple to 4.3 mVrms at a switching frequency of 118 MHz. With an optimized design the modulator achieves a maximum efficiency of 87.5% and a small signal -3 dB bandwidth of 285 MHz. At 10 dB back-off the efficiency is more than 40%. The modulator can deliver 22.7 dBm output power to a 5.3 Omega load. It satisfies the linearity requirement of IEEE 802.11g WLAN signal when tested in a real polar modulated amplifier.