A − 137 dBm/Hz Noise, 82% Efficiency AC-Coupled Hybrid Supply Modulator With Integrated Buck-Boost Converter

Abstract

This paper presents a hybrid supply modulator (SM) with a comprehensive analysis of receiver (RX) band noise in an envelope tracking power amplifier (ET-PA). The designed SM supports both ET mode and average power tracking (APT) mode depending on the PA output power level. In the APT mode, an integrated buck-boost (BB) converter with hysteretic control generates dc supply voltage and its average switching frequency ranges from 1 to 2 MHz. In the ET mode, the bandwidth of SM is determined by a linear amplifier, which has about 30 MHz of signal bandwidth. To improve the ET efficiency, an ac coupling capacitor, with an adaptive offset control, and scaled linear supply are used. The scaled linear supply is provided by the BB converter. To lower the output noise of the SM, a parallel class-AB output buffer and resonance frequency tuning schemes are applied in this paper. For long term evolution 10 MHz with quadrature phase shift keying modulation and 5.8 dB peak-to-average power ratio, the designed SM achieves 82% efficiency at 800 mW output power with a fixed 8 $\Omega $ resistor. Adapting the proposed SM to a PA, a 10 dB ET operation dynamic range is achieved while achieving a power added efficiency of 42.6% at 27 dBm PA output power. The measured SM output noise is −137 dBm/Hz at 95 MHz offset with the PA load, and the PA RX band noise is −124 dBm/Hz, which is dominated by the stand-alone PA itself. The chip is implemented with a 130 nm CMOS process and the die size is 5.0 mm2.