This paper describes an 802.15.6 compliant 2360-2484 MHz multiband transmitter that digitally multiplexes the appropriate phases from an 800 MHz poly-phase filter output to generate π/4 DQPSK signals at 2.4 GHz using injection locking. Modulation at one-third the RF frequency reduces the transmitter power consumption and enables channel selection using an integer-N PLL running at 800 MHz.
The modulation technique does not require phase calibration and resolves the problems of traditional injection lock based modulators. The prototype transmitter consumes 2.4 mW while delivering -10 dBm RF power at the TX output resulting in an energy efficiency of 2.5 nJ/bit at 1.2 Mbps raw data rate. The measured RMS EVM for π/4 DQPSK modulation is 3.21%.