LOW POWER DESIGN VLSI

about low power VLSI

1. LOW POWER DESIGN VLSI Presented By: Ameena Khatun Nishi 2013-2-55-030 Md.Rabiul Islam Tamim 2014-1-55-037 Md Nurujjaman 2013-3-53-006 Mohammad Touhidul Islam 2014-1-55-018

2. CONTENT Abstract INTRODUCTION Importance Of Low Power Design Sources of Power Dissipation Basic principle of low power Design Low Power Design Space Supply voltage reduction Physical Capacitance Switching Activity Low Power Strategies Low power techniques ,CAD Methodologies and Techniques , Power Minimization Techniques Advantages and Disadvantages Conclusion

3. Abstract The recent trends in the developments and advancements in the area of low power VLSI Design are surveyed in this paper. Though Low Power is a well established domain, it has undergone lot of developments from transistor sizing, process shrinkage, voltage scaling, clock gating, etc., to adiabatic logic. This paper aims to elaborate on the recent trends in the low power design.

4. INTRODUCTION Due to integration of components increased the power comes in lime light It is much important that handheld devices must possess low power devices For better performance For long run time (Battery time)

5. Importance O f Low P ower Design Power is considered as the most important constraint in embedded systems Low power design is essential in: High-performance systems ( reason : excessive power dissipation reduces reliability and increases the cost imposed by cooling systems and packaging) portable systems ( reason : battery technology cannot keep the pace with large demands for devices with light batteries and long time between recharges)

6. Sources of Power Dissipation The power dissipation in circuit can be classified into three categories as described below . Dynamic power consumption Short-circuit current Leakage current

7. Dynamic power consumption : Due to logic transitions causing logic gates to charge/discharge load capacitance. Short-circuit current:  In a CMOS logic P-branch and N-branch are momentarily shorted as logic gate changes state resulting in short circuit power dissipation. Leakage current:  This is the power dissipation that occurs when the system is in standby mode or not powered. There are many sources of leakage current in MOSFET. Diode leakages around transistors and n-wells, Sub threshold Leakage, Gate Leakage, Tunnel Currents etc. Increasing 20 times for each new fabrication technology. Went from insignificant to a dominating factor.

8. Principle of low power design Using the lowest possible supply voltage Using the smallest geometry, highest frequency devices but operating them at the lowest possible frequency. Using parallelism and pipelining to lower required frequency of operation. Power management by disconnecting the power source when the system is idle. Desigining systems to have lowest requirements on subsystem performance for the given user level functionality.

9. Low Power Design Space Three parts that we can perform low power techniques to reduce power dissipation Voltage Physical Capacitance Switching activity

10. Supply voltage reduction Voltage reduction offers an effective means of power reduction A factor of two reduction in supply voltage yields a factor of four decreases in power consumption But the performance is also getting reduced To avoid the above stated problem, Threshold voltage should be scaled down

11. Physical Capacitance Dynamic power consumption depends linearly on the physical capacitance being switched So minimizing capacitance offers another technique to for minimizing power consumption The capacitor can be kept as small by.. Minimum logic Smaller devices Fewer and shorter wires

12. Switching Activity There are two components to switching activity : which determines the average periodicity of data arrivals E ( sw ) which determines how many transitions each arrival will generate Switching activity is reduced by Selecting proper algorithms architecture optimization, Proper choice of logic topology Logic level optimization which results in less power

13. Calculation of Switching Activity Input Pattern Dependence Logic Function Logic Style Circuit Structure

14. Low Power Strategies

15. Low power techniques

16. Low power techniques Clock Gating To reducing dynamic power dissipation works by taking the enable conditions attached to registers, and uses them to gate the clocks Power Gating High Vt sleep transistors which cut off VDD from a circuit block when the block is not switching Also known as MTCMOS - Multi-Threshold CMOS

17. CAD Methodologies and Techniques Low power VLSI design can be achieved at various levels of the design process System Design inactive hardware modules may be automatically turned off to save power Behavioral Synthesis The behavioral synthesis process consists of three steps: Allocation Assignment and scheduling These steps determine how many instances of each resource are needed Logic Synthesis Physical Design

18. Power Minimization Techniques Reducing chip and package capacitance Process development such as SOI with partially or fully depleted wells Advanced interconnect substrates such as Multi-Chip Modules (MCM). Scaling the supply voltage Very effective But often requires process technologies Employing better design techniques The investment to reduce power by design is relatively small Using power management strategies Various static and dynamic power management techniques

19. Conclusion Low power VLSI is needed Increasing of handheld devices Increasing of complex device structure Long battery life Long device life