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16-Channel Brain
Tissue Stimulator
Friday, February 24
Design Team
Team Members
Marty Grasse – Team Leader
 Erik Yusko – Communications
 Tony Wampole – BWIG
 Danielle Ebben – BSAC
Client
 Dr. Matthew Jones, Dept. of Physiology
Advisor
 Professor Willis Tompkins
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Overview
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Problem Statement
Background
Client Requirements
Design Alternatives
1) Power and signal isolation
2) Amplitude of current waveform control
3) Method of current waveform generation
Conclusion
Future Work
Problem Statement
In order to stimulate neurons in a more
realistic manner, an electrical device is
needed to independently control current
through each electrode in a 16-electrode
array. The device must use parallel logic
from a computer to control the current. The
device must be isolated from electrical noise
so the measurements are accurate.
Background
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Brain functions via network of electrical
circuitry (neurons)
Excite brain tissue by applying electrical
impulses
Observing the tissues response to impulses
is imperative to understanding of brain
physiology as well as brain disorders
Background (Dr. Jones’ work)
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In vitro stimulation of rodent brain tissue
Specifically interested in timing and
connectivity of signal transfer within a neural
circuit
Currently using a large single electrode to
stimulate tissue
Needs multiple small electrodes to deliver
varying magnitudes of current to precise
locations in tissue
Block Diagram
Voltage to
Current
Converter
Power Isolation
and voltage
step up
Electrode
Array
Client Specifications
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Supply a current
stimulus using parallel
logic from computer to
gate
Isolated from AC noise
(60 Hz)
Independent gain
adjustment for each
channel
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Range: 0 mA to 1 mA
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Electrode impedances
up to 3 MOhms
Square pulse 25 to 200
usec
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Very fast rise/fall time
Rack-mount chassis
Power Isolation and Supply
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60 Hz AC noise
Methods of Isolation
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Battery
DC/DC Converters
Reference [11]
Power Isolation and Supply
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Large voltage necessary to guarantee current
across electrodes
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DC/DC converters in series
+
+
+
+
+
+
-
Vs
Output voltage
is significantly
larger than
source voltage
Current Control: VIC
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Load
Reference: [2]
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Transconductance
amplifier: V to I
Δ Vo receive a
corresponding current
value.
IL = Vo*gm where gm is
transconductance of
the VIC
Current Control Continued
Advantages:
 Less Expensive
 Control the
sensitivity of the
circuit
Disadvantages:
 Not commercially
designed and
assembled
 Independent voltage
source required for
V1
Pulse Control: Potentiometer
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Q1
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On/Off control
provided by TTL
output from PC
TTL gates transistor
Q1 on/off
Vo is controlled by
pot, R9.
Pulse Control: Digital
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TTL Analog Stream:
-use an A/D converter
-digitally set current output
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Advantages:
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Flexibility
Resolution
Accuracy
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Disadvantages:
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Limited Digital resolution
Workaround: requires
microcontroller and timing
circuitry
Conclusion
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Power isolation over Battery supply
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DC/DC converters
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Potentiometers to vary voltage input
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Voltage to current conversion
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Self-construction
Two in One
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Analog Devices 1B23
Future Work
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Test sample voltage to current converters
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Decide on final design
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Construct and test final design
References
1) Brasil, R.O. Leal-Cardoso, J.H. An optically coupled power stimulus isolation unit with
high voltage and fast rise time output. Brazilian Journal of Medical and Biological
Research. 1999. P. 767-771
2) Kaczmarek, Kurt A. Kramer, Kevin M. Webster, John G. Radwin, Robert G. A 16Channel 8-Parameter Waveform Electrotactile Stimulation System. IEEE
Transactions on Biomedical Engineering. Vol. 38, 10. October 1991.
3) Wu, Han-Chang. Young, Shuenn-Tsong. Kuo, Te-Son. A Versatile Multichannel
Direc-Synthesized Electrical Stimulator for FES Applications. IEEE Transactions on
Instrumentation and Measurement. Vol. 51, 1. February 2002.
4) Land, Bruce R. Johnson, Bruce R. Wyttenbach, Robert S. Hoy, Ronald R. Tools for
Physiology Labs: Inexpensive Equipment for Physiological Stiumulation. The Journal
of Undergraduate Neuroscience Education. June, Fall 2004.
5) Poletto, Christopher J. Van Doren, Clayton L. A High Voltage, Constant Current
Stimulator for Electrocutaneous Stimulation Through Small Electrodes. IEEE
Transactions on Biomedical Engineering. Vol. 46, 8. August 1999.
6) Wikipedia. Current Source. Recovered 1-30-2006. [Online]
http://en.wikipedia.org/wiki/Current_source
7) Elliot, Rod. A Beginner’s Guide to Potentiometers. Recovered 2-06-06. [Online]
http://sound/westhost.com/pots/htm
References II
8)
9)
10)
11)
Wagenaar, Daniel A. Potter, Steve M. A versatile all-channel stimulator for
electrode arrays, with real-time control. Journal of Neural Engineering. Vol. 1.
2004. p. 39-45
Tehovnik, Edward J. Electrical stimulation of neural tissue to evoke behavioral
responses. Journal of Neuroscience Methods. Vol. 65. 1996. p.1-17
Cogan, Stuart F. Troyk, Philip R. Ehrlich, Julia. Plante, Timothy D. In Vitro
Comparison of the Charge-Injection Limits of Activated Iridium Oxide (AIROF) and
Platinum-Iridium Microelectrodes. IEE Transactions on Biomedical Engineering.
Vol. 53, No. 9, September 2005.
Ledwich, G. 1998 [Online] Recovered February 20, 2006
http://www.powerdesigners.com/InfoWeb/design_center/articles/DCDC/converter.shtm