Title :
Combined Linear and
-Modulated Switch-Mode PA Supply Modulator for Polar Transmitters
Author :
Kitchen, Jennifer N. ; Chu, Connie ; Kiaei, Sayfe ; Bakkaloglu, Bertan
Author_Institution :
Ubidyne Inc., Tempe, AZ
Abstract :
A combined linear and delta-modulated (DeltaM) switch-mode PA supply modulator for polar transmitters in wireless handsets is designed in a 0.25 mum CMOS process. The modulator employs a DeltaM switch-mode DC-DC buck converter to enhance the efficiency of a linear regulator at backed-off supply voltages and powers. The delta-modulator´s noise-shaping characteristic, linear regulator´s power supply rejection, digital pre-emphasis of the input envelope, and a closed-loop amplitude path from the PA output are simultaneously used to achieve state-of-the-art modulator performance. The presented supply modulator follows the input signal´s envelope with 20 dB output dynamic range, maximum efficiency of 75.5% at an output power of 30.8 dBm, and 75 dB SFDR for envelope signals up to 4 MHz occupied RF bandwidth. For a 1625 kb/s 8 PSK RF input signal at 900 MHz, polar modulation of a commercial low-power GSM-900 PA provides 10 dB ACPR improvement.
Keywords :
CMOS integrated circuits; DC-DC power convertors; cellular radio; delta modulation; low-power electronics; mobile handsets; power amplifiers; radio transmitters; ACPR; CMOS process; DeltaM switch-mode DC-DC buck converter; PA output; PSK RF input signal envelope; RF bandwidth; SFDR; backed-off supply power; backed-off supply voltage; bit rate 1625 kbit/s; closed-loop amplitude path; commercial low-power GSM-900 PA; delta-modulated switch-mode PA supply modulator; delta-modulator\´s noise-shaping characteristics; frequency 4 MHz; frequency 900 MHz; linear regulator; linear regulator\´s power supply rejection; polar modulation; polar transmitter; power amplifier; size 0.25 mum; state-of-the-art modulator performance; wireless handset; Buck converters; CMOS process; Delta modulation; Power supplies; RF signals; Radio frequency; Regulators; Telephone sets; Transmitters; Voltage; Delta $(Delta)$ modulator; linear regulator; polar modulation; power amplifiers; switching amplifiers;
Journal_Title :
Solid-State Circuits, IEEE Journal of
DOI :
10.1109/JSSC.2008.2011010