Design techniques for passive wireless microsystems

The unique advantage of harvesting power wirelessly has evolved passive wireless microsystems to a fast-growing high-impact technology. In this dissertation, several new design techniques are proposed for the increasingly stringent requirements of passive wireless microsystems. The absence of on-board batteries imposes ultralow power consumption of passive wireless microsystems. Recent research reveals that multi-voltage systems-on-a-chip dramatically reduce power consumption such that power-efficient on-chip voltage level shifters are critically needed. This dissertation proposes a novel set of voltage level shifters built upon diode-based clamper-rectier configurations. The voltage level shifters are passively powered by incoming signals with no static current consumption and are able to shift the incoming signals bidirectionally to suit the different voltage domains. The shifting steps could be continuous and are not bounded by the discrete transistor thresholds and power rails. A second bottleneck of passive wireless microsystems is the wireless power-harvesting efficiency that limits the wireless communication distance and the on-chip circuitry complexity and functionality. This dissertation proposes a transformer-based impedance matching network that greatly improves the power transfer efficiency from the receiving antenna to the on-chip circuit loads. The transformer is also capable of automatically calibrating its input impedance to match to the antenna impedance by a novel low-power varactor current tuning technique. In passive wireless microsystems, data modulation scheme largely determines the power transmission efficiency and data communication speed. Exploiting the constant carrier envelop of FSK modulation, this dissertation proposes a dual-tank architecture for FSK receivers in passive wireless microsystems. The dual receiving tanks significantly improves the power conversion efficiency of on-chip AC-to-DC voltage multipliers by providing high-quality-factor resonating tank voltages at each of the alternating FSK carriers. High data transmission rate is also achieved by exploring the dual tanks in an all-digital and a voltage-level shifting FSK demodulators.