1. Day 31: November 26, 2012 Inductive Noise
ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems
Day 31: November 26, 2012
Inductive Noise
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2. Today Inductive Responses Calculating L Where do inductances show up
Impact of inductance on digital circuits
How address
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3. Response
What happens here?
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4. LC Response V2
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5. LC Response
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6. LC Response
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7. LC Response
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8. LC Response
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9. LC Response
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10. LC Response
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11. LC Response
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12. Response?
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13. RLC Response V2
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14. RLC Response
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15. RLC Response
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16. Solving for w
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17. RLC
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18. RLC
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19. RLC For What happens? What else happens? Oscillation Decay
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20. RLC Response (R=100)
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21. When Oscillate For what R does this particular circuit oscillate?
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22. RLC Response
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23. Inductance of Wire
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24. Inductance: Wire over Ground Plane
Inductance per cm with h=3mil, w=5mil?
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25. Lwire
C and L per unit length
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26. Chip Inductance Cwire = 0.16 pF (for the 1mm) Cwire = 0.16nF/m
Permeability m0≈ mSi02=12.6×10-7H/m
Permitivity eox=3.5×10-11F/m
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27. On Chip Cwire = 0.16 pF (for the 1mm) Cwire = 0.16nF/m
Permeability m0≈ mSi02=12.6×10-7H/m
Permitivity eox=3.5×10-11F/m
276 pH (for 1 mm)
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28. Comparisons 5mil trace on PCB Protoboard wires (0.6mm diameter)
About 7nH/cm
On chip wire
0.28nH/mm = 2.8nH/cm
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29. Inductors Bond pads Chip leads Long wire runs Cables
Src:
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30. Where Arise
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31. Signal Path
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32. Power Ground
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33. Shared Power/Ground Example: 74x04
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34. Estimate Req, Ceq for gates in parallel 250 gates switching at clock
R0 = 25K W
C0 = 0.01 fF
say 10C0=0.1fF for typical load
250 gates switching at clock
Req = 100W Ceq=25fF
Assume L=1nH
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35. Power Ground
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36. RLC Response
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37. Today’s Chips
How many gates?
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38. Multiple Power/Ground Pins
Use many power/ground pins
How many pins on a package?
Divide switching gates by pins
To get effective load on each pin
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39. How Improve
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40. Minimize the L Make wires short Use power and ground planes
Think of power plane as a very wide wire
Impact on C and L?
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41. Add Good C’s Bypass Capacitors – inside the inductances On board
On package
On chip
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42. Bypass Capacitor Example
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43. Bypassed Supplies (@ transistor)
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44. Bypassed Output
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45. Minimize Current Draw More Power/Ground Pins Slower rise/fall times
Spread out switching
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46. Idea Long wires are inductive Bypass capacitors help Avoid them
Especially on power supplies
Bypass capacitors help
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47. Admin Wednesday Lecture Thursday: Project 2 due Friday in Lab
Lab instructions out Wednesday
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