A 13 pJ/bit 900 MHz QPSK/16-QAM Band Shaped Transmitter Based on Injection Locking and Digital PA for Biomedical Applications

This paper presents a 900 MHz highly digital transmitter capable of providing band shaped QPSK/16-QAM modulation for high data-rate applications with high energy efficiency. Injection-locked ring oscillator is used for multi-phase carrier generation which eliminates the use of power-hungry phase-locked loop. It also provides fast settling time that enables heavy duty cycling to maximize energy conservation. Direct modulation at power amplifier is adopted to simplify the transmitter architecture. Fabricated in 65 nm CMOS, the transmitter achieves maximum data rate of 50 Mbps/100 Mbps for QPSK/16-QAM with effective sideband suppression more than 38 dB. The chip occupies an active area of 0.08 mm and achieves a settling time of less than 88 ns. Under 0.77 V supply, it achieves an energy efficiency of 26 pJ/bit and 13 pJ/bit with and without band shaping respectively. The measured EVM is better than 6% for QPSK (at 50 Mbps) and 16-QAM (at 100 Mbps) while delivering -15 dBm of output power.