UCLA

Internet of Things (IoT) has recently become a crucial technology in our daily lives that has applications ranging from managing airports’ passenger flow to taking care of the elder. It aims at connecting all appliances and products to create a vast network of applications. An IoT system is composed of leaf nodes that collect data from different applications which then transmit the data to a gateway or hub and eventually for storage and processing in the cloud. Battery life is a key bottleneck for leaf nodes that are either mobile or distributed without a fixed power connection. In order to communicate with a very low power budget, wake-up receivers (WuRx) that are part of a power management unit are needed in order to extend a device's service period.

While several approaches to wake-up a leaf node is possible such as using a watchdog timer that periodically and systematically wakes up the device, this work, we target leaf nodes with high throughputs and accessed in an asynchronous manner by a centralized hub. Such a WuRx imposes specific challenges including low wake-up latency, high data rate, good sensitivity, and ultra-low power budget targeting a battery life >10 years. Existing designs do not satisfy all challenges for the WuRx system or the battery power management efficiencies at such low power. Hence, we propose a new WuRx technique with the sub-microwatt power management unit that significantly bridges the gap between the required and achievable performance. New integrated circuit techniques are implemented in CMOS chip such as building Schottky diode on CMOS, a novel data-locking oscillator technique, and a digital correlation unit to identify signatures from the hub.

Existing solutions for low voltage regulation suffer from low power efficiency especially with load currents that transitions from nano-watts to milli-watts. In this dissertation, we first propose a two-stage hybrid power management unit (PMU) that employs a highly-efficient novel ON-OFF LDO as the second stage and uses a switched-capacitor dc-dc divider as the first stage. This design is then enhanced to operate across a wide range of loads from sub-microwatt to 100’s of microwatts by using selectable sizing of its switches to improve efficiency to >95% across the target range of load current. The output voltage that is divided from the first stage is then regulated using the proposed ON-OFF LDO with a dropout voltage of <30mV. The hybrid architecture regulates battery voltage to 0.4V and achieves a power efficiency of >85% for the wake-up receiver as the load.

Lastly, when the main transceiver receives the wake-up signal, it requires a short time for settling so that it communicates the necessary information to the gateway quickly. The main transceivers consume in order of 10s of milli-Watts which is regulated through an LDO. Existing solutions could not provide short settling with small overshoot for a fast start-up. We propose a novel LDO that uses a new Coarsely-Quantized Class-D control that enables wide loop bandwidth using a multi-level and pulse-width modulated (MLPWM) gate control of the output device. The flipped voltage follower (FVF) output stage is adopted with a feed-forward derivative path to limit overshoot/undershoot. The proposed LDO settles within 280ns when the load is stepped in 7ns from 0 to 300mA with no observed overshoot or undershoot.