Low-power VLSI Design of Fuzzy Logic Based Automatic Controller for Total Artificial Heart

1. Low-power VLSI Design of Fuzzy Logic Based Automatic Controller for Total Artificial Heart Bashir I. Morshed Department of Electronics

2. References [1] H. Cheung-Hwa, "Fuzzy logic automatic control of the Phoenix-7 total artificial heart", Japanese Society for Artificial Organs, accepted for publication on Feb. 2004. [2] H. C. Kim, et al., "Development of a microcontroller based automatic control system for the electrohydraulic total artificial heart", IEEE Trans. Biomedical Engineering, vol. 44, no. 1, pp. 77 - 89, 1997. [3] M. Sasaki, et al., "Fuzzy multiple-input maximum and minimum circuits in current mode and their analyses using bounded-difference equations", IEEE Trans. Computers, vol. 39, no. 6, pp. 768 - 774, 1990. [4] M. Sasaki, F. Ueno, "A Fuzzy logic function generator (FLUG) implemented with current mode CMOS circuits", Intl. Symp. Multiple-Valued Logic, pp. 356 - 362, 1991. [5] M. Sasaki, F. Ueno, "A VLSI implementation of Fuzzy logic controller using current mode CMOS circuits", Intl. Conf. Industrial Fuzzy Control and Intelligent Systems, pp. 215-220, 1993. [6] M. Sasaki, F. Ueno, "A Novel Implementation of Fuzzy logic controller using new meet operation", IEEE Conf. Fuzzy Systems, vol. 3, pp. 1676-1681, 1994.

3. Contents • Introduction • Artificial heart • Controller algorithms • Fuzzy logic • Fuzzification and defuzzification • Design challenges • Preliminary results • Time table • Conclusion

4. Objective • To design an automatic controller to be used in totally-implantable artificial heart. • Desired properties: • Low-power and high speed operation, • Real-time monitoring and control, • Proper operation within some supply voltage variation, • Self-regulating and adaptive. • Suitable techniques: • Fuzzy logic based control algorithm, • CML based CMOS (full-custom ASIC) technology. • Design challenges: • CML based special circuitry to implement Fuzzy functions, • Combining CML blocks to implement Fuzzy logic blocks.

5. Introduction • Artificial hearts are being implanted to the patients with critical heart problems, so that they can survive until a heart transplant is possible. • Milestones: • 1952: First successful open heart surgery by F. John Lewis. • 1967: Christiaan Barnard performs the first whole heart transplant. • 1982: Willem DeVries first implanted a permanent artificial heart designed by Robert Jarvik. • Ongoing researchers are focusing on durable and adaptive artificial hearts so that they can operate independently and reliably without any human control or monitoring.

6. Controller Simplified blocks of TAH [2] Total Artificial Heart (TAH) • A TAH is an implantable device entirely replacing the human heart for a certain period of time. • Must be capable of doing all functions of heart according to specific needs of human body. • Two mechanical pumps (diaphragm type) replace the ventricles and are controlled by internal electronic device.

7. Proposed Configuration [2]

8. Controller for TAH • Automatic controller monitors and regulates: • heart rate, • percent systole, • drive pressure, separately for both of the left and the right ventricles. • Factors to be considered: • Patient's physical activity, • requirement of oxygen circulation, • blood pressure at preload and afterload, • Starling's Response, etc.

9. Some Interesting Phenomena • Starling's Response: deals with the variable heart volume and rate needed for specific individual. • The well trained athlete's heart rate does not increase as much nor as quickly as that of an average individual during strenuous activity. • Pulmonary edema: if the right ventricle is over-driven, then fluid can actually be forced into the lungs. • The amount of blood flowing from the right ventricle has to be sufficient enough to supply the required amount of blood to the left ventricle. • The pressure at afterload on the right ventricle must be less compared to that of the left side.

10. Controller Algorithm • Various controlling algorithms and techniques: • PID based, • RAM/ROM lookup table based, • Fuzzy logic based, etc. • The advantages of Fuzzy logic based controller: • Simple rule based operation makes FL very fast, • Potential for real-time automatic control eliminating continuous manual monitoring under varying hemodynamic conditions, • Inherent adaptability property of the logic, • Highly stable nature and nonlinear control surface, • No ADC/DAC.

11. Controller Design • Design options: • Micro-controller based, • PLA/PAL based, • Full custom ASIC. • Advantage of full custom ASIC: • Efficient and compact design blocks of Fuzzy rules using current mode logic (CML) [3-6], • Very low power and high speed of operation, • Efficient implementation of control algorithm.

12. Fuzzy Logic (FL) • Lotfi A. Zadeh (1973) is the founder of Fuzzy logic. • It is basically a convenient way to map an input space to an output space. • The basic idea is soft computing alike human logic. • Rather than attempting to model a system mathematically, FL incorporates a simple rule-based approach to a solving control problem IF (X) AND/OR (Y) THEN (Z). • There are mainly two different models: • Mamdani • Sugeno

13. Discrete vs Continuous Logic Continuous Logic (Fuzzy) Discrete Logic (Digital)

14. Precision vs Significance Digital Robot Fuzzy Robot

15. Structure of Fuzzy Logic

16. Membership Functions

17. Fuzzification and Defuzzification

18. Mamdani Model

19. Sugeno Model

20. Example 1 (Mamdani): Rules If then If then If then

21. Example 1 (Mamdani): Surface

22. Example 2 (Sugeno): Rules If or then If and then If or then

23. Example 2 (Sugeno): Surface

24. Conventional vs Fuzzy Logic

25. Design Challenges • Design/verification of the following functional blocks: • Minimum/Maximum operation (current mode), • FL Function generator (FLUG) with rules block, • Membership function circuit, • Meet operation (replacing weighted average), • Bias circuit, variable gain current mirror, etc. • Modifications to adopt membership functions other than Gaussian and Mamdani model. • Combining the basic blocks and acceptable operation with supply voltage variation. • Compatible input/output to meet requirements of TAH.

26. Preliminary Results

27. Preliminary Results (cont.) Delay effect Minimum device size

28. Time Table

29. Conclusion • Project goals: • The designs proposed by Sasaki will be tested on CMOS 0.18u technology. • A few design blocks of the Fuzzy controller for TAH will be designed, tested and verified. • Proper operation for operating voltage variation within certain degree of errors. • Limitations for simulation: • Modeling TAH and various parameters associated with that. • The adaptability property.