Low-Power CMOS Design

1. Low-Power CMOS Design For Advanced VLSI Design and VLSI Signal Processing Courses 12-04-2002 台大電機系 吳安宇 教授

2. Data Source • “Low-power Circuit Design Basics,” by Prof. Jan M. Rabaey, UC Berkerly, in tutorial of ISCAS, London, 1994. • “Can we simultaneously achieve High Speed and Low Power in IC Design?” by Prof. Wentai Liu in 7th VLSI/CAD Symposium, 1996. • Chapter 17 of Textbook. 台灣大學 吳安宇 教授

3. Low Power Design – An Emerging Discipline • Historical figure of merit for VLSI design – performance (circuit speed) and chip area (circuit density/cost). But • Power dissipation is now an important metric in VLSI design. • No single major source for power savings across all design levels – Required a new way of THINKING!!! • Companies lack the basic power-conscious culture and designers need to be educated in this respect. • Overall Goal – To reduce power dissipations but maintaining adequate throughput rate. 台灣大學 吳安宇 教授

4. Motivation - Microprocessor 台灣大學 吳安宇 教授

5. Motivation - Microprocessor 台灣大學 吳安宇 教授

6. Competitive Reasons – Low Power • Battery Powered Systems – Extended Battery Life and reduce weight and size. • High-Performance Systems • Cost • Package (chip carrier, heat sink, card slots, plenum, …) • Power Systems (supplies, distribution, regulators, …) • Fans (noise, power, reliability, area, …) • Operating cost to customer – Energy Star issue. • Reliability • Failure rate increase by 4X for Tj @ 110C vs 70C • Mission critical operation at 100C • Size and Weight – Product footprint (office and deskspace) 台灣大學 吳安宇 教授

7. The Power Crisis : Portability Expected Battery Lifetime increase Over next 5 years: 30-40% PDA, Cellular Phone, Notebook Computer,etc. 台灣大學 吳安宇 教授

8. A Multimedia Terminal – The Infopad Present day battery technology (year 1990) – 20 lbs for 10hrs 台灣大學 吳安宇 教授

9. IC Design Space 台灣大學 吳安宇 教授

10. Low Power Design • Source of power disspation • P = P switching + P short-circuit + Pleakage + P static • Definitions: • Switching power P = CV2fα • Short circuit power P = IscV • Leakage power P = IleakageV • Static power P = IstaticV • α : switching activity factor • Low power design would look at the trade-offs of the above issues 台灣大學 吳安宇 教授

11. Dynamic Power Consumption • Not a function of transistor sizes! • Need to reduce CL, Vdd, and f ti reduce power • Reduce the probability, P0 -> 1 Energy/transition = CL * Vdd2 Power = Energy/transition * f = CL * Vdd2 * f 台灣大學 吳安宇 教授

12. Dynamic Power Consumption - Extended • Power = Energy/transition * transition rate = CL * Vdd2 * f0->1 = CL * Vdd2 * P0->1 * f = CEFF * Vdd2 * f • Power Dissipation is Data Dependent Function of Switching Activity • CEFF = Effective Capacitance = CL * P0->1 台灣大學 吳安宇 教授

13. Ultra Low Power System Design • Power minimization approaches: • Run at minimum allowable voltage • Minimize effective switching capacitance 台灣大學 吳安宇 教授

14. Process • Progress in SOI and bulk silicon • (a) 0.5V operation of ICs using SOI technology • (b) 0.9V operation of bulk silicon memory, logic, and processors • Increasing densities and clock frequencies have pushed the power up even with reduce power supply 台灣大學 吳安宇 教授

15. Choice of Logic Style 台灣大學 吳安宇 教授

16. Choice of Logic Style • Power-delay product improves as voltage decreases • The “best” logic style minimizes power-delay for a given delay constraint 台灣大學 吳安宇 教授

17. Power Consumption is Data Dependent • Example : Static 2 Input NOR Gate Assume : P(A=1) = ½ P(B=1) = ½ Then : P(Out=1) = ¼ P(0→1) = P(Out=0).P(Out=1) =3/4 * 1/4 = 3/16 CEFF = 3/16 * CL 台灣大學 吳安宇 教授

18. Transition Probability of 2-input NOR Gate as a function of input probabilities 台灣大學 吳安宇 教授

19. Switching Activity (α) : Example 台灣大學 吳安宇 教授

20. Glitching in Static CMOS 台灣大學 吳安宇 教授

21. At the Datapath Level… Irregular Reusable 台灣大學 吳安宇 教授

22. Balancing Operations 台灣大學 吳安宇 教授

23. Carry Ripple 台灣大學 吳安宇 教授

24. Data Representation 台灣大學 吳安宇 教授

25. Low Power Design Consideration (cont’) (Binary v.s. Gray Encoding) 台灣大學 吳安宇 教授

26. Resource Sharing Can Increase Activity (Separate Bus Structure) 台灣大學 吳安宇 教授

27. Resource Sharing Can Increase Activity (cont’d) 台灣大學 吳安宇 教授

28. Operating at the Lowest Possible Voltage • Desire to operate at lowest possible speeds (using low supply voltages) • Use Architecture optimization to compensate for slower operation Approach : Trade-off AREA for lower POWER 台灣大學 吳安宇 教授

29. Reducing Vdd 台灣大學 吳安宇 教授

30. Lowering Vdd Increases Delay • Concept of Dynamic Voltage Scaling (DVS) 台灣大學 吳安宇 教授

31. Architecture Trade-offs : Reference Data Path 台灣大學 吳安宇 教授

32. Parallel Data Path 台灣大學 吳安宇 教授

33. Pipelined Data Path 台灣大學 吳安宇 教授

34. A Simple Data Path : Summary 台灣大學 吳安宇 教授

35. Computational Complexity of DCT Algorithms 台灣大學 吳安宇 教授

36. Power Down Techniques • Concept of Dynamic • Frequency Scaling (DFS) 台灣大學 吳安宇 教授

37. Energy-efficient Software Coding • Potential for power reduction via software modification is relatively unexploited. • Code size and algorithmic efficiency can significantly affect energy dissipation • Pipelining at software level- VLIW coding style • Examples - 台灣大學 吳安宇 教授

38. Power Hunger – Clock Network (Always Ticking) • H-Tree – design deficiencies based on Elmore delay model • PLL – every designer (digital or analog) should have the knowledge of PLL • Multiple frequencies in chips/systems – by PLL • Low main frequency, But • Jitter and Noise, Gain and Bandwidth, Pull-in and Lock Time, Stability … • Local time zone • Self-Timed • Asynchronous => Use Gated Clocks, Sleep Mode 台灣大學 吳安宇 教授

39. Power Analysis in the Design Flow 台灣大學 吳安宇 教授

40. Human Wearable Computing - Power • Wearable computing – embedding computer into clothing or creating a form that can be used like clothing • Current computing is limited by battery capacity, output current, and electrical outlet for recharging 台灣大學 吳安宇 教授

41. Conclusions • High-speed design is a requirement for many applications • Low-power design is also a requirement for IC designers. • A new way of THINKING to simultaneously achieve both!!! • Low power impacts in the cost, size, weight, performance, and reliability. • Variable Vdd and Vt is a trend • CAD tools high level power estimation and management • Don’t just work on VLSI, pay attention to MEMS – lot of problems and potential is great. 台灣大學 吳安宇 教授

42. Applications • Portable Multimedia Terminal • Wireless C&C • System on Chip (From Dr. Yang of Windbond) 台灣大學 吳安宇 教授

43. Applications IWireless Computing/Communication 台灣大學 吳安宇 教授

44. Applications IIA Portable Multimedia Terminal 台灣大學 吳安宇 教授

45. Applications IIISystem Value of IC Product • Concept of lays 台灣大學 吳安宇 教授

46. Applications IVSystem on Chip • Entire system function • Logic + Memory • More than two types of devices • Allow more freedom in architecture • Const/Performance trade-off 台灣大學 吳安宇 教授

47. Applications VNew Opportunity for Taiwan IC Industry • PAST • Digital IC • µ P • IBM Compatible + MD-DOS • FUTURE • System On Chip • Reduce head-on competition on standard products • Technology will be available • Manufacturing Service available • Same starting point as other countries • Can have more R/D focus 台灣大學 吳安宇 教授