Design and CMOS Technology Optimization of a Low Power MEMS Pierce Oscillator
thesisposted on 05.11.2016, 00:00 by Emmanuel C. Onyema
Particulate matter (PM) consists of air pollutants such as dust, smoke, diesel exhaust and tobacco fumes. A subset of these pollutants, which are PM particles with diameter less than or equal to 2.5 (PM2.5), are a major health hazard. According to the United states Environment Protection Agency (EPA), over 9000 deaths annually are due to exposure to (PM2.5). Thus there is the need for monitoring personal exposure to these pollutants. Available PM sensors are either too expensive or too bulky to be carried about. The Air-Microfluidics group has developed a compact and affordable personal (PM2.5) sensor. At the heart of the PM sensor, lives a Micro Electro-Mechanical Systems (MEMS) Pierce Oscillator consisting of a CMOS sustaining amplifier in a feedback loop with an FBAR (Film Bulk Acoustic Wave Resonator). The Air-Microfluidic circuit is built in such a way that when (PM2.5) is deposited on the FBAR’s surface, a change in its resonant frequency is induced, and the rate of this frequency change corresponds to the particle concentration in the sampled volume of air. This thesis work has been proposed for incorporation into the Air-Microfluidic group's (PM) sensor project. This work designs a CMOS sustaining amplifier capable of driving a 650 MHz MEMS FBAR thus realizing a pierce oscillator. Low phase noise, Low power consumption and good signal strength are some desired qualities of properly designed oscillators. Therefore meticulous design procedure should be adhered to if set specifications are to be attained. The main purpose of this work is to develop an optimization methodology for the chosen sustaining amplifier topology to ensure the scalability of the design across CMOS process technologies. Moreover, an adequate Electrostatic Discharge (ESD) protection structure has been included in the design for safeguarding against human-related ESD events.