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10/27/05 ELEC 5970-001/6970-001 Lecture 16 1
ELEC 5970-001/6970-001(Fall 2005)Special Topics in Electrical EngineeringLow-Power Design of Electronic Circuits
Adiabatic and Charge Recovery Logic
Vishwani D. AgrawalJames J. Danaher Professor
Department of Electrical and Computer EngineeringAuburn University
http://www.eng.auburn.edu/[email protected]
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 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
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 3
Reexamine CMOS Gate
i = Ve-t/RpC/Rp
i2Rp
VV2/Rp
C
Time, t
Po
we
r
Most energy dissipated here
V2e-2t/RpC/Rp
0
Energy = Area = CV2/2
v(t)
V v(t)
v(t
)
3RpC
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 4
Charging with Constant Current
i = K i2Rp
V(t)
C
Po
we
r0
v(t) = Kt/C
Time to charge capacitor to voltage V v(T) = V = KT/C, or T = CV/KCurrent, i = K = CV/T
Ou
tpu
t vo
ltag
e, v
(t)
0
V
Time, t t=CV/K
Kt/C
Power = i2Rp = C2V2Rp/T2
Energy = Power × T = (RpC/T) CV2
C2V2Rp/T2
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 5
Or, Charge in Steps
i = Ve-t/RpC/2Rp
i2Rp
0→V/2→V
V2/4Rp
C
Time, t
Po
we
r
V2e-2t/RpC/4Rp
0Energy = Area = CV2/8
v(t)
V v(t)
v(t
)
V/2
Total energy = CV2/8 + CV2/8 = CV2/4
3RpC 6RpC
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 6
Energy Dissipation of a Step
TE = ∫ V2e-2t/RpC/(N2Rp) dt 0
= [CV2/(2N2)] (1 – e-2T/RpC)
≈ CV2/(2N2) for large T ≥ 3RpC
Voltage step = V/N
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 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 → ∞
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 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.
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 9
Dynamic CMOS Inverter
V
C
v(t)
CK
vin
CK
vin
v(t)
P E P E P E
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 10
Adiabatic Dynamic CMOS Inverter
C
v(t)
CK
vin
A. G. Dickinson and J. S. Denker, “Adiabatic Dynamic Logic,” IEEE J. Solid-State Circuits, vol. 30, pp. 311-315, March 1995.
CK
vin
v(t)
V
0
V-Vf
0
Vf+
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 11
Cascaded Adiabatic Inverters
CK1 CK2 CK1’ CK2’
vin
CK1
CK2
CK1’
CK2’
precharge
input
evaluatehold
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 12
Complex ADL Gate
CK
B
A. G. Dickinson and J. S. Denker, “Adiabatic Dynamic Logic,” IEEE J. Solid-State Circuits, vol. 30, pp. 311-315, March 1995.
AC
AB + C
Vf < Vth
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 13
Quasi-Adiabatic Logic• 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)
D1
D2
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 14
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, i.e. energy is recovered (RESTORE phase)
Quasi-Adiabatic Logic Design
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 15
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.
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 16
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
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 17
Technology Distribution• Microprocessor has a mix of static CMOS
and Quasi-adiabatic components
ALUALU• Adder-subtractor unit• Barrel shifter unit• Booth-multiplier unit
ALUALU• Adder-subtractor unit• Barrel shifter unit• Booth-multiplier unit
Control UnitsControl Units• ARM controller unit• Bus control unit
Pipeline UnitsPipeline Units• ID unit• IF unit• WB unit• MEM unit
Control UnitsControl Units• ARM controller unit• Bus control unit
Pipeline UnitsPipeline Units• ID unit• IF unit• WB unit• MEM unit
Quasi-Adiabatic Static CMOS
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 18
Power AnalysisDatapath
Component
Power Consumption (mW)
Frequency 25 MHz
Power Consumption (mW)
Frequency 100 MHz
Quasi-adiabatic
* Static CMOS
Power Saved
Quasi-adiabatic
* Static CMOS
Power Saved
32-bit Adder Subtracter
1.01 1.55 44% 1.29 1.62 20%
32-bit Barrel Shifter
0.9 1.681 46% 1.368 1.8 24%
32-bit Booth Multiplier
3.4 5.8 40% 5.15 6.2 17%
Power Consumption (mW)
Frequency 25 MHz
Quasi-adiabatic
* Static CMOS
Power Saved
60 mW 85 mW 40%
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 19
Power Analysis (Cont’d.)
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 20
Area AnalysisDatapath
Component
Area (mm2)
Quasi-adiabatic
* Static CMOS Area Increase
32-bit Adder Subtracter 0.05 0.03 66%
32-bit Barrel Shifter 0.25 0.11 120%
32-bit Booth Multiplier 1.2 0.5 140%
Chip Area (mm2)
Quasi-adiabatic
* Static CMOS
Area Increase
1.01 1.55 44%
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10/27/05 ELEC 5970-001/6970-001 Lecture 16 21
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.