A 500-MHz Bandwidth 7.5-mVpp Ripple Power-Amplifier Supply Modulator for RF Polar Transmitters

Chul Kim, Chang Seok Chae, Young Sub Yuk, Chris M. Thomas, Yi Gyeong Kim, Jong Kee Kwon, Sohmyung Ha, Gert Cauwenberghs, Gyu Hyeong Cho

Research output: Contribution to journalArticlepeer-review


The parallel combination of a switching and a linear amplifier in the supply modulator for RF power amplifiers (PAs) has the potential to enhance energy efficiency while achieving wider bandwidth and lower ripple output voltage. In this paper, a linear amplifier that features a buffered-switching Class-AB bias scheme is presented for the supply modulator in polar-transmitter structures achieving 500 MHz of small-signal 3-dB bandwidth at a 1.2-V supply. The linear amplifier absorbs and cancels up to 60 mA of ripple current from the switching amplifier. As such, the ripple in the output voltage of the hybrid linear-switching supply modulator is less than 7.5 mVpp. The switching amplifier provides most of the signal current for greatest efficiency owing to a proposed rail-to-rail current-sensing circuit. Current feedback in the switching amplifier achieves 1.68-MHz unity-gain bandwidth at 6-MHz switching frequency. Harmonic distortion in the output voltage of the supply modulator is below 40 dBc at 0.8 Vpp sinusoidal input up to 9 MHz. The peak efficiency is 87.7% for a 8.25- Ω load, while the maximum output power is 23.6 dBm for a 4.99- Ω load. The chip measures 1.35 mm2 in a 65-nm standard bulk CMOS process.

Original languageEnglish (US)
Pages (from-to)1653-1665
Number of pages13
JournalIEEE Journal of Solid-State Circuits
Issue number6
StatePublished - Jun 2018


  • Class-AB bias
  • current feedback
  • current sensing
  • envelope elimination and restoration
  • hybrid supply modulator (HSM)
  • open-loop gate driver polar transmitter
  • three-stage amplifier
  • wide bandwidth

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


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