A Robust Power-Scalable Transmitter Architecture for Wireless Body Area Networks

Abstract

In this dissertation, an RF transmitter is presented that uses closed-loop PLL- based BFSK modulation and is reconfigurable for both the MedRadio and 433 MHz ISM bands. A power efficient class-C amplifier is utilized and the design methodologies for designing a highly efficient and low-power amplifier are discussed in detail. The mediocre PVT performance of the classical implementation of the class-C power amplifiers is a major cause of concern that inhibits widespread usage of these types of amplifiers. An open-loop ultra-low power calibration loop is designed to deal with process, temperature and voltage drifts. Also introducing for the first time, a digitally tunable power amplifier core with a single reconfigurable matching network is able to vary the output power level from -12 dBm to -2dBm while maintaining similar efficiency numbers. A completely integrated PLL is used in the frequency synthesis. BFSK modulation is performed by switching the divide ratio of a dual modulo divider and a low-power NMOS delay-based ring-VCO acts as the oscillator. Several performance records are achieved: (1) The PA realizes a peak efficiency of 47% in the high-power (ISM) (-2 dBm) mode and 43% (33%) in the MedRadio -12 dBm (-16 dBm backoff) modes. (2) The PLL dissipates only 72 &muW with a phase noise of -111 dBc/Hz @ 1 MHz. (3) The overall transmit efficiencies are 29% and 17% for the -12 dBm and -16 dBm backoff levels for the MedRadio band and 44% for the ISM (433 MHz) bands. (4) The PVT compensation loop reduces the standard deviation by 59% compared to the classical implementations.