Transcript Pr cis

A Prototype FPGA Tile for SubthresholdOptimized CMOS
Peter Grossmann, Miriam Leeser
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Low power systems benefit from FPGAs
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Improved energy efficiency/performance vs. microcontroller
Improved design via reconfigurability
Lower cost vs. ASIC
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State of the art low power FPGAs: 10s to 100s of mW
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Ultra-low power applications require 10s to 100s of µW
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Wireless sensor networks
RFID
Digital hearing aids
Ultra-low power budgets motivate extreme voltage scaling
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Subthreshold supply voltages yield peak energy efficiency
This work is funded by the Lincoln Scholars Program, MIT Lincoln Laboratory. The Lincoln Laboratory portion of
this work was sponsored by the United States Government under Air Force contract number FA8721-05-C0002. The opinions, interpretations, conclusions and recommendations are those of the authors and are not
necessarily endorsed by the United States Government.
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Subthreshold vs. Superthreshold
Circuits
H yp o th e tic a l M O S I-V C u rv e
Key Tradeoffs in
Subthreshold Operation:
0 .0 0 1
0 .0 0 0 1
· High energy efficiency
D ra in C u rre n t (A )
1 E -0 5
1 E -0 6
· Large circuit delays
1 E -0 7
VTH
1 E -0 8
1 E -0 9
· High sensitivity to
process variation
1 E -1 0
1 E -1 1
1 E -1 2
0
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
G a te -S o u rc e V o lta g e (V )
ID  I0
W
L
V GS  V TH
e
nV T
 V DS

V
1  e T

Subthreshold
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ID  I0
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V GS
 V TH
2
· Low sensitivity to
transistor size
· High sensitivity to
supply voltage
Superthreshold
MIT Lincoln Laboratory
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Prototype Tile Architecture
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2-input CLB
Tile Boundary
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4 routing channels
24
SRAM,
Programming
Circuitry
ASEL[1]
ASEL[0]
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YSEL[0]
A
32 programming bits
YSEL[1]
CLB
ASEL[0]
Y
YSEL[2]
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BSEL[0]
Flexible I/O
BSEL[1]
YSEL[3]
B
BSEL[0]
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Prototype Tile Demonstration
A
B
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10
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0
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10
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D
Q
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Functional verification of all tile
components through
implementation of serial adder
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Tile average power ≈ tens of
nanowatts
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Enables useful circuits on sub-mW
power budgets
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Implementation of 6x6 tile array on
test chip currently in fabrication at
Lincoln Laboratory
SUM
CIN
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10
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Serial Adder
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COUT
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