Download - Low-Power SRAM Using 0.6 um Technology
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Low-Power SRAM Using0.6 um Technology
Andrew AshworthJonathan ChenMatt Williams
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Introduction
• Metrics: Power(mW), Delay(ns), Area(mm2)• Low Power SRAM:
(total power)2 * delay * area
• SRAM size of 1 Mb• Word size of 32 bits• One read or one write access per cycle
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Clock
• Two-phase non-overlapping clock generator
CLK CLK1
CLK2
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Array Architecture• Block Selector, Transmission Gates, and Positive
Edge Triggered Register
5:32
<4:7>
<0:3>
<8:11>
<12:15>
<16:19>
<20:23>
<24:27>
<28:31>
0 1 2 3
4 5 6 7
8 9 10 11
12 13 14 15
16 17 18 19
20 21 22 23
24 25 26 27
28 29 30 31
A14A13A12A11A10
Word-line Enable Bit
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Block Architecture
• Hierarchical word line with divided bit line
Local BL
Local BLB
Local WL
Local WL
Transistors use 0.5 um technology. Sizes shown represent widths of devices.
1.5um1.5um
1.5um
4.5um
4.5um
To local word-line
Numbers shown by inverters are ratios relative to minimum sized inverter
1 4
A9A8A7A6
A5A4A3A2
Enable bit from 5:32 Decoder
4:16
4:16
1 4
1 4
Enable bit
Enable bit
4:16
4:16
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Block Architecture Continuedfrom Figure 5
Global Bit-Line Global Bit-Line Bar
Divided bit line approach with 16 bit cells per local bit line
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Drowsy Cache
•An extra 6t bit cell holds whether block is asleep or awake and selects corresponding Vdd•Requires extra dc-dc converters on chip
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Layout
• Horizontal bit cell to maintain square block• We should have learned SKILL
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Challenges
• Drivers• Clock generation – iterated through 3 designs
before finally settling on a pulsed NOR design.• Designing sense amp enable driver
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Simulation
• Extracted parasitic capacitances from layout to build accurate array model
• Simulated model of one block to represent entire array
• Began with worst case 50C and SS to find stable clock
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Results
• The SRAM correctly performed a write followed by a read at all process corners, and temperatures
• As VDD is scaled down, leakage power decreases by orders of magnitude. We have no reliable numbers as power simulations returned unrealistic results for 5V VDD
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Results II
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Metric
• Total Size: about 500mm^2• Average Power: about 9mW• Delay: about 35ns• Total Metric: 1.458 million
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Questions?