Download Advanced VLSI Design - Washington State University

EE 587
SoC Design & Test
Partha Pande
School of EECS
Washington State University
[email protected]
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Final Exam Review
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System Level Design Issues
• SoC Interconnection Architectures
– Drawback of bus-based systems in terms of timing, power
and other relevant parameters
• Role of parallelism
• Problem with long wires
– Buffer Insertion
– Problems with classical buffer insertion
– How to deal with that
• Multi-processor SoC (MP-SoC) platform design
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Signal Integrity
• Crosstalk Avoidance
– Comparative study of different CAC schemes
– How to cascade multiple CAC blocks for a wide bus so that
there is no crosstalk between two sub blocks
• Except coding what are the different methods of reducing
coupling
• Effect of inductance on buffer insertion
• Effect of inductance on propagation delay
• Electromigration
• L di/dt noise
• Decoupling capacitance
• IR drop in power lines
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Clock & Power Routing
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How to control IR drop and L di/dt noise
What is the advantage of interleaved power & ground routing
Different ways of reducing power in clocking
Different clock routing mechanisms
Advantages Tapered H-tree
Configuration of gated clock
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SoC Testing
• What are the principal challenges in SoC testing
• Design of scan flip-flop
• How can you modify a pass transistor-based latch to make it
scanable
• JTAG instructions
• LFSR pattern generation
• Given a polynomial you need to derive the LFSR configuration
• How you can modify a BILBO for different modes of operations
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IDDQ Testing
• What is bridging fault and how you can detect it
• Applicability of IDDQ test in SoCs, what is the challenge?
• How to switch off static current dissipating components for IDDQ
testing. You need to explain with the help of proper circuit level
design details
• Relation between JTAG and IDDQ testing
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Iddq Testing in SoC
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Methods of Reducing Power
• Architectural Decisions – has the highest impact (parallelism,
pipelining, low activity designs, lower frequency operation )
• Circuit Techniques – gated clocks, low glitch circuits, reduce
capacitances, reduce activity
• Recent developments – Vdd scaling, VT adjustments
• Software – low power instructions, algorithms
• CAD tools to implement low-power techniques
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Circuit Design Styles
• Nonclocked Logic
– CMOS, Pseudo-NMOS, Differential Cascade Voltage Switch
(DCVS), Pass-Transistor
• Clocked Logic
– Domino, Differential Current Switch Logic (DCSL)
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Circuit Design Styles
• Advantages of DCSL gates
• Principle of skewed CMOS
• Dependence of short circuit current & leakage current on the
skew ratio
• Role of Vdd and Vt scaling
• Principle of MTCMOS
• Difference between logic and memory circuits in terms of Vdd
and Vt scaling
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MTCMOS
• In active mode, low-VT MOSFET’s achieve high speed.
• In standby mode when St'by signal is high, high-VT MOSFET’s in series to
normal logic circuits cut off leakage current.
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Issues in MTCMOS
• Virtual ground not actual ground (lose some noise margin)
• Can increase width of sleep transistor to reduce voltage at virtual ground but
it will also increase subthreshold leakage and area of sleep transistor
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Variable Threshold-CMOS
• Threshold voltage of both devices are increased by adjusting the body-bias
voltage in order to reduce subthreshold leakage current in standby mode
• Requires twin-tub technology so that substrates of individual devices can be
adjusted
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Low Swing Interconnects
• Dynamically Enabled Drivers
• Low Swing Bus
• Different level converter circuits
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Dynamic Power Management
• Dynamically reconfigures an electronic system to provide the
requested services and performance levels with a minimum
number of active components or a minimum load on such
components
• Selectively turns off or reduce the performance of idle or
partially unexploited components
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DPM Techniques
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Predictive Technique
Static Technique
Adaptive Technique
Clock gating
Supply shut down
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Low Power SRAM Design
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Banked Organization
Divided Word Line
Pulsed Word line
Bit Line Isolation
Suppressing leakage in SRAM
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Power & BIST
• Modern design and package technologies make external testing
increasingly difficult, and BIST has emerged as a promising
solution to the VLSI testing problem
• BIST is a DFT methodology aimed at detecting faulty
components in a system by incorporating test logic on chip.
• In BIST, an LFSR generates test pattern
• LFSR-generated tests tend to take longer to reach acceptable
levels of fault coverage, which increases the total energy
consumption
• Test vectors applied at nominal operating frequency will have a
higher average power dissipation than normal mode. This is
because in normal mode, successive functional input vectors
applied to a given circuit have significant correlation; the
consecutive vectors of an LFSR generated test sequence have
a lower correlation.
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Final Exam
• 6-7 questions
• Wire Engineering, SoC Design & Test, Low Power Design
– These broad topics will be equally represented
• Try to answer as much as you can
• I will be testing you on whatever I have taught
• Class Notes are very important
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