LOW POWER AMPLIFIERS FOR RECORDING ACTIVITY OF ELECTRICALLY ACTIVE CELLS ...

111 Pages·2003·0.94 MB·English

ABSTRACT
Title of Thesis: LOW POWER AMPLIFIERS FOR RECORDING
ACTIVITY OF ELECTRICALLY ACTIVE CELLS

Makeswaran Loganathan, Master of Science, 2003

Thesis directed by: Dr. Pamela Abshire
Department of Electrical and Computer Engineering

Biological applications that require sensing individual cells have led to
developments in the synthesis of large multielectrode arrays and single cell
isolating microstructures. This in turn drives the need for the integration of low
power electronic circuitry at or very close to the site of activity. We describe low
voltage low power CMOS amplifiers that address this need by rejecting DC
offsets, and have tunable bandwidths. They operate at 1.35V, with a power
consumption of 37.8µW and have an input referred noise of 23µV. We also
describe the design of a wireless transmission system capable of transmitting the
electrical signals sensed from cells. Integration of the amplifier array with the
wireless link brings continuous monitoring of neurophysiologic activity of
unanesthized and freely moving animals closer to realization. The transmitter is
capable of generating an ASK modulated signal at a power level of -36 dBm at a
frequency of 820 MHz.
LOW POWER AMPLIFIERS FOR RECORDING ACTIVITY OF
ELECTRICALLY ACTIVE CELLS

by

Makeswaran Loganathan

Thesis submitted to the Faculty of the Graduate School of the
University of Maryland, College Park in partial fulfillment
of the requirements for the degree of
Master of Science
2003

Advisory Committee:

Dr. Pamela Abshire, Chair
Dr. Ralph Etienne-Cummings
Dr. Timothy Horiuchi
Dr. Elisabeth Smela
© Copyright by
Makeswaran Loganathan
2003
Dedication

To my parents and my sister

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ACKNOWLEDGEMENTS
I thank my advisor Dr. Pamela Abshire for her invaluable guidance and
support during the course of my thesis. Without her motivation and
encouragement this work would not have been possible.
I would also like to thank Dr. Ralph Etienne-Cummings, Dr. Timothy
Horiuchi, and Dr. Elisabeth Smela for their assistance through various technical
discussions, and taking time off to serve on my thesis committee.
Thanks to Dr. Junghwan Kim and Russell for spending a lot of their
valuable time and resources in helping me make the RF measurements. Dr. Reza
Ghodssi and Alireza Modafe were very resourceful in letting me use their probe
station for characterization.
Colleagues at the IBIS lab were very helpful, resourceful and fun-loving
and made my stay here very rewarding. I would like to thank them all, especially
Suvarcha Malhotra for helping me with the Bio-amplifiers, Somshekar Bangalore
Prakash for his help with the RF transmitter, and Hong Hao Ji for the several
technical discussions that we had. I would also like to thank Jack Chaiyupatumpa,
Kory Schoenfloss, Natasha Reeves and Jean-Marie Lauenstein for helping me
during the course of my thesis.
I would also like to thank my dear friends who were ever so willing to
help me, especially Harini Raghunthan, Ranjani Sridharan, Deepika
Krishnaswamy, Arvind Aiyar and Suresh Kumar.
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My parents’ constant support and encouragement helped me identify and
pursue opportunities in research and higher education. Thanks to them and to my
sister Deepika for making significant contributions in my life.

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TABLE OF CONTENTS
List of Tables ………………………………………………………………........ix
List of Figures…………………………………………………………………......x
1. Introduction……………………………………………………………......1
1.1 Design Specifications……………………………………………...3
1.2 Overview………………………………………………………......4

2. Review of Medical Instrumentation and Biological Recordings…….........7
2.1 Introduction……………………………………………………......7
2.2 Amplifiers for Medical and Biological purposes……………….....8
2.3 Microstructures and microtechniques…………………………....14

3. Bio-amplifier Design………..…………………………………………...17
3.1 Introduction……………………………………………………....17
3.2 Device Specifications, Layouts and Test Results………………..22
3.3 Performance comparison with existing designs……………..…...26
3.4 Packaging for Interaction with cells……………………………..28
3.5 Power Supply requirement of the Bio-Amplifier………………..30

4. Low Power Techniques………………………………………………......32
4.1 Introduction……………………………………………………....32
4.2 Circuit Blocks…………………………………………………....33
4.2.1 Transistor………………………………………………...33
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4.2.2 Current Mirror…………………………………………...34
4.2.3 Transconductor…………………………………………..36
4.2.4 Voltage Gain Units……………………………………....37
4.3 Voltage Follower Technique………………………………….....38

5. Low Voltage Techniques applied to the Bio-Amplifier……………...46
5.1 Voltage Follower………………………………………………...46
5.2 Level Shifting…………………………………………………....47
5.3 Design Considerations…………………………………………...49
5.4 Noise Analysis……………………………………………..…….53
5.5 Test and Measurement Results…………………………………..54
5.5.1.1 Amplifier with PMOS differential pair and NMOS input
stage……………………………………………………………...54
5.5.1 2 Discussion of Measurement Results……………………….….....55
5.5.2.1 Amplifier with NMOS differential pair and PMOS
input…............…………………………………………………...57
5.5.2 2 Discussion of Measurement Results……............………….….....59
5.5.3.1 Amplifier with Source Follower configuration……............…......59
5.5.3 2 Discussion of Measurement Results…….............…………….....61
5.6 Conclusions……………………………………………………....61

6. Wireless Transmission System…………………………………….….....63
6.1 Introduction……………………………………………………....63
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6.2 Voltage Controlled Oscillator…………………………………....64
6.3 Pre-Amplifier………………………………………………….....66
6.4 Power Amplifier……………………………………………….....67
6.4.1 Choice of Scheme for Power Amplifier……………….....67
6.4.2 Choice of Passive elements and transistor dimensions......69
6.4.3 Improvement of performance of the PA for ASK
scheme…………………………………………………....70
6.4.4 Realization of On-Chip Inductors……………………......71
6.5 Layouts…………………………………………………………...74

7. RF Test and Measurement………………………………………….........77
7.1 Inductance……………………………………………………......77
7.2 VCO……………………………………………………………...78
7.3 Pre-Amplifier………………………………………………….....80
7.4 Transmitter…………………………………………………….....80
7.5 Conclusions……………………………………………………....82

8. Conclusions……………………………………………………………....84
8.1 Amplifiers……………………………………………………......84
8.2 Wireless Transmission System…………………………………..85
8.3 Future Work……………………………………………………...85

Appendix………………………………………………………………………....87
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