A 90μW MICS/ISM Band Transmitter with 22% Global Efficiency

For fully autonomous implantable or body-worn devices running on harvested energy, the peak and average power dissipation of the radio transmitter must be minimized. We propose a highly integrated 90μW 400MHz MICS band transmitter with an output power of 20μW leading to a 22% global efficiency — the highest reported to date for such systems. We introduce a new transmitter architecture based on cascaded multi-phase injection locking and frequency multiplication to enable low power operation and high global efficiency. Our architecture eliminates slow phase/delay-locked loops for frequency synthesis and uses injection locking to achieve a settling time < 250 ns permitting very aggressive duty cycling of the transmitter to conserve energy. At a data-rate of 200 kbps, the transmitter achieves an energy efficiency of 450 pJ/bit. Our 400MHz local oscillator topology demonstrates a figure-of-merit of 204 dB.