seminar: Baris Cagdaser - Monday March 16 3-4pm CIS 101X

Peter Chen jwpchen at stanford.edu
Tue Mar 10 14:54:48 PDT 2009


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Resonant Circuits for Low Voltage Electrostatic Drive and Position Sensing
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Monday, March 16, 2009
CIS 101X 3:00-4:00pm
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Baris Cagdaser
Senior Integrated Circuits Designer
InvenSense, Sunnyvale, CA
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Abstract
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This talk presents a single MEMS electrostatic interface circuit that 
does not require high voltage electronics, but does provide high 
voltage actuation, position sensing, and extends the range of 
parallel-plate actuators.
Electrostatic actuation finds widespread use in micromechanical 
systems. Despite being simple in implementation, achieving a 
sufficiently large force is often challenging.  Increasing the 
actuator voltage results in increased force, but requires special 
interfaces with high voltage electronics.  Furthermore, position 
feedback is commonly used to control the dynamic response of the 
actuator. In principle, the position dependent actuation capacitance 
can be used for sensing.  But, in practice, measuring this capacitance 
is challenging due to small levels of signal and large feedthrough 
from the drive system.  So, most actuators need separate sense 
electrodes as well as circuit techniques such as time division 
multiplexing.
The core of the proposed circuit is an electrical RLC tank formed by 
the actuation capacitor and an inductor.  When driven at its 
electrical resonance, the tank amplifies the voltage across the 
actuator capacitor.  So, the actuation voltage becomes much higher 
than the drive signal provided by electronics.  The prototype 
implementation uses only a 4Vpeak drive signal to actuate a MEMS 
mirror that requires 45VDC under conventional voltage control.  Since 
the actuator capacitor is position dependent, achieving the maximum 
amplification requires an oscillator circuit that automatically 
follows the tank’s electrical resonance frequency as the actuator 
moves.  So, the actuator motion translates the oscillator frequency, 
which is now used to measure the MEMS displacement in the same 
interface circuit.  Finally, the position dependent nature of the tank 
also increases the range of parallel-plate actuators by providing 
inherent position feedback and changing the pull-in behavior.


Biography
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Baris Cagdaser received his BS degree from the Middle East Technical 
University in Ankara, Turkey, where he worked with Prof. Tayfun Akin 
on MEMS capacitive ice detectors.  During his PhD studies at the 
University of California at Berkeley, he worked with Prof. Bernhard E. 
Boser focusing on MEMS interface electronics.  Specifically, he 
developed a low voltage electrostatic interface for electrostatic 
actuation and position sensing.  This circuit was used for the 
positioning of MEMS micro-mirrors.  Since earning his PhD degree in 
2005, Baris Cagdaser has been with InvenSense, a Silicon Valley MEMS 
start-up company, as a Senior IC Designer working on integrated 
interface electronics for MEMS inertial sensors.



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