Outlooks on Transmitter Energy Efficiency and FOM and a 189.7-dBJ/bit ULP DPPM Transmitter

Abstract

In this paper, we compare in a new way the energy efficiencies of modulations that have been popular in ultra-low power (ULP) transmitters. The comparison considers how the choice of modulation affects the combined energy consumed per bit (EPB) by the carrier synthesizer and power amplifier (PA). The comparison includes on-off keying (OOK), binary phase-shift keying (BPSK), binary frequency-shift keying (BFSK), pulse-position modulation (PPM) and differential PPM (DPPM). The results suggest that using OOK, BPSK or BFSK can consume tens to hundreds of percents more energy per bit compared to PPM and DPPM. Furthermore, a new energy efficiency figure of merit (FOM) is derived for transmitters. It accounts for consumed power, output power, data rate, signal bandwidth and signal-to-noise ratio required by the utilized modulation. The FOM can be applied to various types of transmitters with numerous modulations. We also present a sub-100 W DPPM transmitter (TX) and a 3.2- W 2-axis gesture sensor interface, implemented in 0.18 m CMOS. The TX operates in the 433-MHz band, uses pulse shaping for improved spectrum and achieves a FOM of 189.7 dBJ/bit. The estimated uplink range is up to 1 kilometer