ELEC 5970-001/6970-001(Fall 2005)
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ELEC 5970-001/6970-001(Fall 2005) Special Topics in Electrical Engineering Low-Power Design of Electronic Circuits Power Consumption in a Memory. Vishwani D. Agrawal James J. Danaher Professor Department of Electrical and Computer Engineering Auburn University

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ELEC 5970-001/6970-001(Fall 2005)Special Topics in Electrical EngineeringLow-Power Design of Electronic CircuitsPower Consumption in a Memory

Vishwani D. Agrawal

James J. Danaher Professor

Department of Electrical and Computer Engineering

Auburn University

http://www.eng.auburn.edu/~vagrawal

[email protected]

ELEC 5970-001/6970-001 Lecture 18


Intuitive architecture
Intuitive Architecture

M bits

S0

Word 0

Word 1

Storage cell

Word 2

N words

Word N-2

Word N-1

SN-1

Input-Output (M bits)

ELEC 5970-001/6970-001 Lecture 18


Memory organization
Memory Organization

Bit line

2L-K

Storage cell

AK

AK-1

AL-1

Word line

M.2K

Sense amplifiers/drivers

A0

AK-1

Column decoder

Input-Output (M bits)

ELEC 5970-001/6970-001 Lecture 18


Cell array power management
Cell Array Power Management

  • Smaller transistors

  • Low supply voltage

  • Lower voltage swing (0.1V – 0.3V for SRAM)

    • Sense amplifier restores the full voltage swing for outside use.

ELEC 5970-001/6970-001 Lecture 18


Sense amplifier
Sense Amplifier

VDD

Full voltage

swing

output

bit

bit

SE

Sense ampl. enable:

Low when bit lines

are precharged and

equalized

ELEC 5970-001/6970-001 Lecture 18


Sram cell
SRAM Cell

VDD

Precharge

circuit

PC

EQ

WL

BL

BL

Output

bit

Sense

amplifier

bit

ELEC 5970-001/6970-001 Lecture 18


Hierarchical organization
Hierarchical Organization

Block 0 Block 1 Block P-1

Row

addr.

Column

addr.

Block

addr.

Global data bus

Control

circuitry

Global amplifier/driver

Block selector

I/O

ELEC 5970-001/6970-001 Lecture 18


Power saving
Power Saving

  • Block-oriented memory

    • Lengths of local word and bit lines are kept small.

    • Block address is used to activate the addressed block.

    • Unaddressed blocks are put in power-saving mode; sense amplifier and row/column decoders are disabled. Power is maintained for data retention.

ELEC 5970-001/6970-001 Lecture 18


Static power
Static Power

1.3μ

1.1μ

900n

700n

500n

300n

100n

8-kbit SRAM

0.13μ CMOS

Leakage current (Amperes)

7x increase

0.18μ CMOS

0.0 0.6 1.2 1.8

Supply voltage

ELEC 5970-001/6970-001 Lecture 18


Adding resistance in leakage path
Adding Resistance in Leakage Path

VDD

Low-threshold transistor

sleep

VDD.int

SRAM

cell array

SRAM

cell array

SRAM

cell array

VSS.int

sleep

GND

ELEC 5970-001/6970-001 Lecture 18


Lowering supply voltage
Lowering Supply Voltage

VDD

VDDL= 100mV for 0.13μ CMOS

Sleep = 1, data

retention mode

sleep

SRAM

cell array

SRAM

cell array

SRAM

cell array

GND

ELEC 5970-001/6970-001 Lecture 18


References
References

  • K. Itoh, VLSI Memory Chip Design, Springer-Verlag, 2001.

  • J. M. Rabaey, A. Chandrakasan and B. Nikolić, Digital Integrated Circuits, Upper Saddle River, New Jersey: Pearson Education, Inc., 2003.

ELEC 5970-001/6970-001 Lecture 18


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