Integrated Implantable Stimulator without Off-Chip Blocking-Capacitors
Presented by:
Shiyad Ashraf
No. 61
College Of Engineering, Trivandrum
2007-11 batch

Contents
Introduction
Working of FES
Need of blocking capacitors
Disadvantages of using blocking capacitors
Methods of protection without off chip capacitors
Technique for avoiding off chip capacitors
Stimulator output stages utilizing blocking capacitors
Current generator circuits
Proposed current generator circuits
Proposed output stage
Stimulator Architecture
Advantages
Conclusion

introduction
Patients suffering from spinal cord injury can use a Functional Electrical Stimulator[FES] to stimulate nerves and muscles below the injury
Conventional FES system uses large value bulky capacitors to ensure adequate safety which increases the physical size of the implant
Newly designed system for FES enables to reduce the capacitor value and hence the physical size of the implant

Working of FES
FES is used to stimulate the nerves and muscles by applying train of current pulses
Each stimulation pulse consist of a cathodic phase followed by an anodic phase
Design of neural stimulators for FES has the benefit from advances in microelectronics and packaging technology
Discrete blocking capacitors are widely used to ensure adequate safety since safety is prime concern
Blocking capacitor limits the charge on the electrodes to Qmax=C.V
Need of blocking capacitors
To ensure safety under faulty conditions
Placed in series with each stimulating electrode
Limits the charge on the electrode to Qmax=C.V
Qmax is chosen as density cannot exceed the safety limit
To maintain charge balance during normal stimulation
Disadvantage of using blocking capacitors
Large capacitance value
Large in size
Determines the size of stimulator
Methods of protection without off chip capacitor
Continuously monitoring of the electrode-tissue impedance, current level and voltage level
Techniques used for avoiding off chip capacitor
New current generator circuit
New stimulator output stage utilizes high frequency current switching
Stimulator output stages utilizing blocking capacitor
Current generator circuits

HFCS Technique
Proposed current generator circuits
Proposed output stage
Stimulator Architecture
Block Diagram

Advantages
Can reduce the value of off chip capacitor to an extreme low level
Capacitor size can be reduced
Entire stimulator can be miniaturized to a chip size

Conclusion
Introduced two circuit techniques to miniaturize the output stage of the implantable neural stimulator
It hoped that this will restore many more functions to people with spinal cord injury than is currently possible

References
Xiao Liu, Student Member, IEEE, Andreas Demosthenous, Senior Member, IEEE, and Nick Donaldson “An Integrated Implantable Stimulator That is Fail-Safe Without Off-Chip Blocking-Capacitors” IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, VOL. 2, NO. 3, SEPTEMBER 2009

N. J. M. Rijkhoff, J. Holsheimer, E. L. Koldewijn, J. J. Struijk, P. E. V. Kerrebroeck, F. M. J. Debruyne, and H. Wijkstra, “Selective stimulation of sacral nerve roots for bladder control: A study by computer modeling,” IEEE Trans. Biomed. Eng., vol. 41, no. 5, pp. 413–424, May 2002.

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