Efficient Energy Recovery in Electronic Circuits

1. ELEC 5270-001/6270-001(Fall 2006)Low-Power Design of Electronic CircuitsAdiabatic Logic Vishwani D. Agrawal James J. Danaher Professor Department of Electrical and Computer Engineering Auburn University, Auburn, AL 36849 http://www.eng.auburn.edu/~vagrawal vagrawal@eng.auburn.edu ELEC 5270-001/6270-001 Lecture 13

2. Examples of Power Saving and Energy Recovery • Power saving by power transmission at high voltage: • 1000W transmitted at 100V, current I = 10A • If resistance of transmission circuit is 1Ω, then power loss = I2R = 100W • Transmit at 1000V, current I = 1A, transmission loss = 1W • Energy recovery from automobile brakes: • Normal brake converts mechanical energy into heat • Instead, the energy can be stored in a flywheel, or • Converted to electricity to charge a battery ELEC 5270-001/6270-001 Lecture 13

3. Reexamine CMOS Gate V2/Rp V Most energy dissipated here i2Rp i = Ve-t/RpC/Rp v(t) Power VI = V2e-2t/RpC/Rp v(t) V C v(t) 3RpC 0 Time, t Energy dissipation = Area/2 = CV2/2 ELEC 5270-001/6270-001 Lecture 13

4. Charging with Constant Current V(t) i2Rp i = K Kt/C V v(t) = Kt/C C2V2Rp/T2 Output voltage, v(t) Power C 0 0 t=CV/K Time, t Time (T) to charge capacitor to voltage V v(T) = V = KT/C, or T = CV/K Current, i = K = CV/T Power = i2Rp = C2V2Rp/T2 Energy dissipation = Power × T = (RpC/T) CV2 ELEC 5270-001/6270-001 Lecture 13

5. Or, Charge in Steps 0→V/2→V i2Rp i = Ve-t/RpC/2Rp V2e-2t/RpC/4Rp v(t) v(t) V2/4Rp V C v(t) Power V/2 0 3RpC 6RpC Energy = Area = CV2/8 Time, t Total energy = CV2/8 + CV2/8 = CV2/4 ELEC 5270-001/6270-001 Lecture 13

6. Energy Dissipation of a Step Voltage step = V/N T E = ∫ V2e-2t/RpC/(N2Rp) dt 0 = [CV2/(2N2)] (1 – e-2T/RpC) ≈ CV2/(2N2) for large T ≥ 3RpC ELEC 5270-001/6270-001 Lecture 13

7. Charge in N Steps Supply voltage 0 → V/N → 2V/N → 3V/N → . . . NV/N Current, i(t) = Ve-t/RpC/NRp Power, i2(t)Rp = V2e-2t/RpC/N2Rp Energy = N CV2/2N2 = CV2/2N → 0 for N → ∞ Delay = N × 3RpC → ∞ for N → ∞ ELEC 5270-001/6270-001 Lecture 13

8. References • C. L. Seitz, A. H. Frey, S. Mattisson, S. D. Rabin, D. A. Speck and J. L. A. van de Snepscheut, “Hot-Clock nMOS,” Proc. Chapel Hill Conf. VLSI, 1985, pp. 1-17. • W. C. Athas, L. J. Swensson, J. D. Koller, N. Tzartzanis and E. Y.-C. Chou, “Low-Power Digital Systems Based on Adiabatic-Switching Principles,” IEEE Trans. VLSI Systems, vol. 2, no. 4, pp. 398-407, Dec. 1994. ELEC 5270-001/6270-001 Lecture 13

9. A Conventional Dynamic CMOS Inverter V P E P E P E CK vin v(t) CK v(t) C vin ELEC 5270-001/6270-001 Lecture 13

10. Adiabatic Dynamic CMOS Inverter P E P E P E P E V 0 CK vin v(t) v(t) vin C Vf + V-Vf 0 CK A. G. Dickinson and J. S. Denker, “Adiabatic Dynamic Logic,” IEEE J. Solid-State Circuits, vol. 30, pp. 311-315, March 1995. ELEC 5270-001/6270-001 Lecture 13

11. Cascaded Adiabatic Inverters vin CK1 CK2 CK1’ CK2’ input CK1 CK2 CK1’ CK2’ evaluate precharge hold ELEC 5270-001/6270-001 Lecture 13

12. Complex ADL Gate AB + C A C Vf < Vth B CK A. G. Dickinson and J. S. Denker, “Adiabatic Dynamic Logic,” IEEE J. Solid-State Circuits, vol. 30, pp. 311-315, March 1995. ELEC 5270-001/6270-001 Lecture 13

13. Quasi-Adiabatic Logic D1 • Two sets of diodes: One controls the charging path (D1) while the other (D2) controls the discharging path • Supply lines have EVALUATE phase ( swings up) and HOLD phase ( swings low) ELEC 5270-001/6270-001 Lecture 13

14. Clocks EVAL. HOLD EVAL. HOLD VDD  0 VDD  0 ELEC 5270-001/6270-001 Lecture 13

15. Quasi-Adiabatic Logic Design • Possible Cases: • The circuit output node X is LOW and the pMOS tree is turned ON: X follows  as it swings to HIGH (EVALUATE phase) • The circuit node X is LOW and the nMOS tree is ON. X remains LOW and no transition occurs (HOLD phase) • The circuit node X is HIGH and the pMOS tree is ON. X remains HIGH and no transition occurs (HOLD phase) • The circuit node X is HIGH and the nMOS tree is ON. X follows  down to LOW. ELEC 5270-001/6270-001 Lecture 13

16. A Case Study K. Parameswaran, “Low Power Design of a 32-bit Quasi-Adiabatic ARM Based Microprocessor,” Master’s Thesis, Dept. of ECE, Rutgers University, New Brunswick, NJ, 2004. ELEC 5270-001/6270-001 Lecture 13

17. Quasi-Adiabatic 32-bit ARM Based Microprocessor Design Specifications • Operating voltage: 2.5 V • Operating temperature: 25oC • Operating frequency: 10 MHz to 100 MHz • Leakage current: 0.5 fAmps • Load capacitance: 6X10-18 F (15% activity) • Transistor Count: ELEC 5270-001/6270-001 Lecture 13

18. Technology Distribution • Microprocessor has a mix of static CMOS and Quasi-adiabatic components Quasi-Adiabatic Static CMOS • ALU • Adder-subtractor • unit • Barrel shifter unit • Booth-multiplier • unit • Control Units • ARM controller unit • Bus control unit • Pipeline Units • ID unit • IF unit • WB unit • MEM unit ELEC 5270-001/6270-001 Lecture 13

19. Power Analysis ELEC 5270-001/6270-001 Lecture 13

20. Power Analysis (Cont’d.) ELEC 5270-001/6270-001 Lecture 13

21. Area Analysis ELEC 5270-001/6270-001 Lecture 13

22. Summary • In principle, two types of adiabatic logic designs have been proposed: • Fully-adiabatic • Adiabatic charging • Charge recovery: charge from a discharging capacitor is used to charge the capacitance from the next stage. • W. C. Athas, L. J. Swensson, J. D. Koller, N. Tzartzanis and E. Y.-C. Chou, “Low-Power Digital Systems Based on Adiabatic-Switching Principles,” IEEE Trans. VLSI Systems, vol. 2, no. 4, pp. 398-407, Dec. 1994. • Quasi-adiabatic • Adiabatic charging and discharging • Y. Ye and K. Roy, “QSERL: Quasi-Static Energy Recovery Logic,” IEEE J. Solid-State Circuits, vol. 36, pp. 239-248, Feb. 2001. ELEC 5270-001/6270-001 Lecture 13