A Sub-100 μW MICS/ISM Band Transmitter Based on Injection-Locking and Frequency Multiplication

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. Additionally, link symmetry must be maintained for peer-to-peer network applications. We propose a highly integrated 90 mu W 400 MHz MICS band transmitter with an output power of 20 mu W, leading to a 22% global efficiency-the highest reported to date for low-power MICS band 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 400 MHz local oscillator topology demonstrates a figure-of-merit of 204 dB while locked to a stable crystal reference. The transmitter occupies 0.04 mm(2) of active die area in 130 nm CMOS and is fully integrated except for the crystal and the matching network.