Sewan Heo

A surface-micromachined MEMS acoustic sensor with X-shape bottom electrode anchor

A surface-micromachined capacitive-type micro-electro-mechanical system (MEMS) acoustic sensor with X-shape bottom electrode anchor on a Si substrate is presented. As it is designed to be implemented on only one side of a substrate for a simple monolithic integrated process, this sensor has X-shape bottom electrode anchor fabricated. The anchor operates to remove the back side process of wafer for a conventional back chamber because the chamber is formed through Si surface etching by an isotropic dry etcher of XeF2. The Si MEMS acoustic sensor proposed in this paper has a diameter of 300 µm and a back chamber depth of 25 µm. It shows a pull down voltage of 9.1 V at 1 kHz and a zero-bias capacitance of 1.87 pF. Additionally, the sensor has an open-circuit sensitivity of 0.57 mV/Pa at 1 kHz on a bias of 5 V.

ADAPTIVE ENERGY MANAGEMENT SYSTEM BASED ON LOW-POWER MICROCONTROLLER WITH ENERGY HARVESTING AT MAXIMUM POWER

This paper describes an energy management system and an algorithm for an energy-aware operation. The system obtains energy from an energy harvester and manages the energy adaptively according to the monitored energy status. Based on a low-power microcontroller, the system controls the energy harvester so that it always harvests energy at maximum power and tracks it when the operating condition changes. It also controls the power consumption of all parts of the system so that they are adjusted dynamically for the management of harvested or stored energy. To manage the energy transfer to a battery, a DC–DC converter, called the energy management IC, is optimized for the operating voltage control of the harvester. In an experiment using an energy harvester and a battery modified for the system, the energy management IC fabricated in a 0.18 μm process maximizes the energy transfer power with a simple, low-power algorithm. The proposed system is verified to be more efficient for low-energy harvesting by the adaptive energy and power management.

High performance of PMSM driver IC integrated sensorless and current sensing circuits

This work proposes high performance of permanent-magnet synchronous motor (PMSM) driver IC integrated with position sensorless scheme and current sensing circuits. The position sensorless scheme is adapted with digital sliding mode observer (SMO) method that has high robust characteristics of motor parameter variations. For current sensing circuits, 10-bit successive approximation (SAR) analog-to-digital converters (ADC) and various (1~16) gain amplifiers are implemented in the fabricated IC. The proposed PMSM driver IC is fabricated with 0.18um BCD process. Compared with the commercial module, with the accurate SMO scheme, a speed error is reduced to 0.7% at 3000rpm and a system efficiency is increased to 1.9 % at 3000rpm, 5N·m. The high precision position estimating driver IC is achieved without any position/current sensors.