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LOW-LEAKAGE REPEATERS FOR NETWORK-ON-CHIP INTERCONNECTS

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Physical layer of NoC. Low link utilization. Most links idle most of ... 4 Low-Leakage Repeaters for NoC Communications ISCAS 2005. Leakage Reduction in Logic ... – PowerPoint PPT presentation

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Title: LOW-LEAKAGE REPEATERS FOR NETWORK-ON-CHIP INTERCONNECTS


1
LOW-LEAKAGE REPEATERS FOR NETWORK-ON-CHIP
INTERCONNECTS
Technion Israel Institute of Technology
  • Arkadiy Morgenshtein, Israel Cidon, Avinoam
    Kolodny, Ran Ginosar

QNoC Research Group Electrical Engineering
Department Technion Israel Institute of
Technology Haifa, Israel
2
Highlights
  • Leakage in NoC links with repeaters
  • Selecting the Repeater Type
  • Optimizing Repeater Insertion
  • Utilization-Oriented Analysis

3
Networks-on-Chip (NoC)
  • NoC characteristics
  • Packet-based data routing
  • Multiple Quality-of-Service levels
  • Physical layer of NoC
  • Low link utilization
  • Most links idle most of the time!
  • Leakage power is important

4
Leakage Reduction in Logic
Subthreshold leakage is dominant at high
temperatures
Solutions
  • more

5
Leakage Reduction in Repeaters
Solutions
?
specific solutions needed
6
Existing Repeater Types
LVT Low-Vt Repeaters
  • fast
  • high leakage

HVT High-Vt Repeaters
  • slow
  • low leakage

SVT - Staggered-Vt
  • fast (In 0?1)
  • slow (In 1?0)
  • low leakage (idle)

16 Sylvester et al.
7
Research Outline
Network-on-Chip
Low Varying Utilization
Selecting the Repeater Type
Optimizing Repeater Insertion

Utilization-Dependant Optimal Number of Repeaters
SR Sleep Repeaters
DTD Dual-Vt Domino Repeaters
Utilization-Oriented Analysis
8
Dual-Threshold Domino (DTD) Repeaters
High-Vt Evaluation Transistors
Low-Vt Pre-charge Transistors
synchronized Clk link
9
DTD Repeaters Operation
  • Precharge transistors disconnected
  • CLK line is synchronized with Data
  • Evaluation by HVT transistors slower but
    tolerant to Vt fluctuations
  • Each Evaluation transistor drives only one
    transistor at next stage faster and can be
    down-sized

10
DTD Repeaters Operation
  • Evaluation transistors disconnected
  • Precharge to low-leakage mode
  • Precharge by LVT transistors - fast

11
DTD Repeaters Operation
X
X
0
0
1
1
X
X
X
X
1
0
1
0
X
X
  • HVT transistors are off low leakage

0
1
0
1
12
DTD Repeaters Operation
X
X
X
X
0
0
1
1
X
X
X
X
X
X
X
X
1
0
1
0
X
X
X
X
  • For Data0 - no transition occurs

13
DTD Repeaters Operation
14
DTD Highlights
  • Application of domino and double-Vt techniques
    to low-leakage repeaters

Benefits Effective leakage reduction during
standby Reduced load on each repeater allowing
downscaling and area reduction Tolerance to VT
fluctuations by using HVT evaluation transistors
Drawbacks - Increased dynamic power consumption
due to signaling in domino protocol - Overhead of
clock line and pre-charge wiring
15
Sleep Transistors in Repeaters
MTCMOS
Logic
Evolution
SR
Repeaters
16
MTCMOS in Repeaters
  • Common sleep transistors insertion
  • Both NMOS and PMOS are used
  • All stages enter and exit sleep mode
    simultaneously
  • LARGE sleep transistors
  • High routing complexity and wiring overhead

17
Repeaters with Per-Stage Sleep Transistor
  • Distributed sleep transistors along the link
  • Each stage of repeaters has a separate pair of
    sleep transistors
  • One stage of repeaters is active
  • - others are in low-leakage
  • standby
  • - Sleep Transistor is heavily loaded and has to
    be scaled with link width

18
Repeaters with Per-Stage Sleep Transistor
  • Distributed sleep transistors along the link
  • Each stage of repeaters has a separate pair of
    sleep transistors
  • One stage of repeaters is active
  • - others are in low-leakage
  • standby
  • - Sleep Transistor is heavily loaded and has to
    be scaled with link width

active
sleep
sleep
19
Repeaters with Per-Stage Sleep Transistor
  • Distributed sleep transistors along the link
  • Each stage of repeaters has a separate pair of
    sleep transistors
  • One stage of repeaters is active
  • - others are in low-leakage
  • standby
  • - Sleep Transistor is heavily loaded and has to
    be scaled with link width

active
sleep
sleep
20
Repeaters with Per-Stage Sleep Transistor
  • Distributed sleep transistors along the link
  • Each stage of repeaters has a separate pair of
    sleep transistors
  • One stage of repeaters is active
  • - others are in low-leakage
  • standby
  • - Sleep Transistor is heavily loaded and has to
    be scaled with link width

active
sleep
sleep
21
SR Sleep Repeaters
Parallel link using individual zigzag sleep
transistors
  • One sleep transistor per repeater
  • Smaller sleep transistors
  • Simpler routing
  • Zigzag connection
  • Only to transistors that are off during sleep
  • Number of sleep transistors is reduced by 50

1
0
0
1
0
0
22
Sleep Repeater Highlights
  • Novel Efficient sleep transistors for repeaters

Benefits Effective leakage reduction during
standby Optimized structure according to
specifics of repeater insertion
Drawbacks - Area overhead - Increased dynamic
power consumption due to additional transistors
23
Simulation Setup
  • 65nm BPTM models for transistors and
    interconnect
  • 32-bit link operating at 105C temperature
  • LVT design was used as baseline for repeater
    insertion
  • Scaling factor was adjusted for SVT, DTD and SR
    to meet the delay target equal to LVT
  • Area, delay and energy were obtained for each
    of the compared techniques

24
Total Repeater Area
DTD smallest area - SR largest area
25
Energy vs. Utilization
  • SVT Least energy at high utilization
  • SR Least energy at low utilization

8mm link
26
Utilization-Dependant Optimal Number of Repeaters
Set Target Delay (DltDopt)
Repeaters Sizing for (1ltKltn)
Optimal K for minimal Leakage Power - Kleak
Optimal K for minimal Dynamic Power - Kdyn
!
Calculate Ratio of Total Power for Kdyn and Kleak
vs. Utilization
Find for which utilization rates k_leak or k_dyn
is optimal
27
Optimal Number of Repeaters
example
  • For each k a suitable sizing factor h is found
    to meet the target delay
  • Optimal k for minimal leakage is kleak4
  • Optimal k for minimal dynamic power is kdyn6

kleak
kdyn
Power vs. k for target D309ps (instead of
Dmin280ps), L10mm
28
Number of Repeaters vs. Utilization
example
  • Total power as function of utilization for Kdyn
    and Kleak
  • Power ratio is calculated for Kdyn and Kleak
  • Break-even point is at 40 utilization
  • The results of Kleak are up-to 17 better at
    low utilization rates

Prefer Kleak
Prefer Kdyn
Power ratio of Kdyn vs. Kleak
29
Summary
  • DTD (Dynamic Dual-Threshold) Repeaters
  • SR (Sleep Repeaters)
  • Zig-zag structure
  • SR least power at low utilization
  • Thanks to low leakage
  • Optimal number of repeaters depends on link
    utilization

30
Questions?
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