Download Evaluation and Characterization of Silicon MESFETs in Low Dropout

School of Electrical, Computer and Energy Engineering
M.S. Final Oral Defense
Evaluation and Characterization of Silicon MESFETs in Low Dropout Regulators
by
Bo Chen
April 16
2:00-3:30 pm
ERC 490
Committee:
Dr. Trevor Thornton (chair)
Dr. Bertan Bakkaloglu
Dr. Michael Goryll
Abstract
The partially-depleted (PD) silicon Metal Semiconductor Field Effect Transistor
(MESFET) is becoming more and more attractive for analog and RF applications due to
its high breakdown voltage. Compared to conventional CMOS high voltage transistors,
the silicon MESFET can be fabricated in commercial standard Silicon-on-Insulator (SOI)
CMOS foundries without any change to the process. The transition frequency of the
device is demonstrated to be 45GHz, which makes the MESFET suitable for applications
in high power RF power amplifier designs. Also, high breakdown voltage and low turnon resistance make it the ideal choice for switches in the switching regulator designs.
One of the anticipated applications of the MESFET is for the pass device for a
low dropout linear regulator. Conventional NMOS and PMOS linear regulators suffer
from high dropout voltage, low bandwidth and poor stability issues. In contrast, the NMESFET pass transistor can provide an ultra-low dropout voltage and high bandwidth
without the need for an external compensation capacitor to ensure stability. In this thesis,
the design theory and problems of the conventional linear regulators are discussed. NMESFET low dropout regulators are designed, evaluated and characterized. The error
amplifier used a folded cascode architecture with gain boosting. The source follower
topology is utilized as the buffer to sink the gate leakage current from the MESFET. A
shunt-feedback transistor is added to reduce the output impedance and provide the current
adaptively. Measurement results show that the dropout voltage is less than 150 mV for a
1A load current at 1.8V output. Radiation measurements were done for discrete MESFET
and fully integrated LDO regulators, which demonstrate their radiation tolerance ability
for aerospace applications.