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A compact large voltage-compliance high output-impedance programmable current source for implantable
Maysam Ghovanloo1, Khalil Najafi
1Bionics Laboratory, Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7914 USA. mghovan@ncsu.edu
IEEE Transactions on Bio-Medical Engineering
|January 18, 2005
Summary
A novel CMOS current source uses voltage-controlled resistors for implantable microstimulators. This design offers high compliance and stable current output, improving efficiency and battery life for neural stimulation devices.
Area of Science:
- Biomedical Engineering
- Electrical Engineering
- Microelectronics
Background:
- Biomedical implantable microstimulators require precise current control for effective neural stimulation.
- Existing current sources often face limitations in voltage compliance and output impedance, impacting efficiency and device longevity.
Purpose of the Study:
- To introduce a new CMOS current source design for biomedical implantable microstimulators.
- To achieve high voltage compliance and stable current output, independent of varying tissue impedances.
Main Methods:
- Utilizing Metal-Oxide-Semiconductor (MOS) transistors in the deep triode region as linearized voltage-controlled resistors (VCR).
- Fabricating a prototype 4-channel microstimulator chip using a standard 1.5-microm CMOS process.
- Characterizing the performance of the VCR current source in terms of voltage compliance, output impedance, and current stability.
Main Results:
- The VCR current source demonstrated large voltage compliance, reaching up to 97% of the supply voltage.
- Achieved high output impedance (> 10 MOmega), maintaining stimulus current constant within 1% variation.
- A 4-channel prototype chip exhibited 425-V compliance and > 10 MOmega output impedance per channel, consuming only 0.05 mm2 chip area.
Conclusions:
- The VCR current source design offers significant improvements in stimulation efficiency and power supply lifetime for implantable devices.
- This technology enables miniaturization and higher current capabilities, crucial for advanced neural stimulation systems.
- A modular 32-site wireless neural stimulation microsystem based on this VCR current source is under development.