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Engineer's summary: Tuned articles of signal integrity design experience
2021-08-20
View：54
Author：IPCB

1. The signal rise time is about 10% of the clock cycle, that is, 1/10x1/Fclock. For example, the rise time in 100MHZ is about 1NS.

2. The amplitude of the Nth harmonic of the ideal square wave is approximately 2/(N pie) times the side value of the clock voltage. For example, the amplitude of the first harmonic of a 1V clock signal is about 0.6V, and the amplitude of the third harmonic is about 0.2V.

3. The relationship between signal bandwidth and rise time is: BW=0.35/RT. For example, if the rise time is 1NS, the bandwidth is 350MHZ. If the bandwidth of the interconnection line is 3GHZ, the shortest rise time it can transmit is about 0.1NS.

4. If the rise time is not known, it can be considered that the signal bandwidth is approximately 5 times the clock frequency.

5. The resonance frequency of the LC circuit is 5GHZ/sqrt (LC), the unit of L is NH, and the unit of C is PF.

6. In 400MHZ, axial pin resistance can be regarded as ideal resistance; in 2GHZ, SMT0603 resistance can be regarded as ideal resistance.

7. The ESL of the axial lead resistance (lead resistance) is about 8NH, and the ESL of the SMT resistance is about 1.5NH.

8. The resistance per unit length of the near bonding wire with a diameter of 1MIL is about 1 ohm/IN.

9. The diameter of 24AWG wire is about 20MIL, and the resistivity is about 25 milliohms/FT.

10. The sheet resistivity of the 1 ounce barrel line is about 0.5 milliohms per square.

11. At 10MHZ, 1 ounce of copper lines begin to have a skin effect.

12. The capacitance of a 1IN spherical surface is about 2PF.

13. A pair of parallel plates the size of a coin. When air is filled between the plates, the capacitance between them is about 1PF.

14. When the distance between the capacitor measuring plates is equal to the width of the plate, the capacitance generated by the edge is equal to the capacitance formed by the parallel plate. For example, when estimating the parallel plate capacitance of a microstrip line with a line width of 10MIL and a dielectric thickness of 10MIL, the estimated value is 1PF/IN, but the actual capacitance is about twice the above, that is, 2PF/IN.

15. If you don't know anything about the properties of the material, but only know that it is an organic insulator, it is considered that its dielectric constant is about 4.

16. For a chip with a power of 1W, the decoupling capacitor (F) can provide charge to make the voltage drop less than 5% for the time (S) is C/2.

17. In a typical circuit board clock, when the dielectric thickness is 10MIL, the coupling capacitance between the power supply and the ground plane is 100PF/IN square, and it is inversely proportional to the dielectric thickness.

18. If the bulk dielectric constant of the 50 ohm microstrip line is 4, then its effective dielectric constant is 3.

19. The local inductance of a round wire with a diameter of 1MIL is about 25NH/IN or 1NH/MM.

20. A toroidal coil with a diameter of 1IN is made from a 10MIL thick line. Its size is equivalent to that of a thumb and an index finger enclosed together, and its loop inductance is about 85NH.

21. The inductance per unit length of a ring with a diameter of 1IN is approximately 25NH/IN or 1NH/MM. For example, if the package lead is part of a loop wire and the length is 0.5IN, its inductance is about 12NH.

22. When the center distance of a pair of round rods is less than 10% of their respective lengths, the local mutual inductance is about 50% of their respective local mutual inductances.

23. When the center distance of a pair of round rods is equal to their own length, the local mutual inductance between them is less than 10% of their respective local mutual inductance.

24. The loop inductance of SMT capacitors (including surface wiring, vias and the capacitor itself) is about 2NH, and it takes a lot of work to reduce this value to below 1NH.

25. The loop inductance per unit area on the plane pair is 33PHx the dielectric thickness (MIL).

26. The larger the diameter of the via, the lower its diffusion inductance. A diffused inductance with a diameter of 25MIL via is about 50PH.

27. If there is a sand hole area, when the free area occupies 50%, it will increase the loop inductance between the plane pairs by 25%.

28. The skin depth of copper is inversely proportional to the square of the frequency. At 1GHZ, it is 2UM. Therefore, at 10MHZ, the skin of copper is 20UM.

29. In a 50 ohm 1 ounce copper transmission line, when the frequency is about higher than 50 MHz, the loop inductance per unit length is a constant. This shows that when the frequency is higher than 50MHZ, the characteristic impedance is a constant.

30. The speed of electrons in copper is extremely slow, equivalent to the speed of an ant, which is 1CM/S.

31. The speed of the signal in the air is about 12IN/NS. The signal speed in most polymer materials is about 6IN/NS.

32. In most rolled materials, the line delay 1/V is about 170PS/IN.

33. The spatial extension of the signal is equal to the rise time X speed, that is, RTx6IN/NS.

34. The characteristic impedance of the transmission line is inversely proportional to the capacitance per unit length.

35. In FR4, the capacitance per unit length of all 50 ohm transmission lines is about 3.3PF/IN.

36. In FR4, the inductance per unit length of all 50 ohm transmission lines is about 8.3NH/IN.

37. For the 50 ohm microstrip line in FR4, the dielectric thickness is about half of the line width.

38. For the 50 ohm strip line in FR4, the spacing between the planes is twice the signal line width.

39. In much less than the return time of the signal, the impedance of the transmission line is the characteristic impedance. For example, when driving a 3IN 50 ohm transmission line, all driving sources with a short rise time and 1NS will experience a 50 ohm constant load during the transmission along the line and the rising transition time.

40. The relationship between the total capacitance and time delay of a section of transmission line is C=TD/Z0.

41. The relationship between the total loop inductance and time delay of a section of transmission line is L=TDxZ0.

42. If the width of the return path in the 50 ohm microstrip line is equal to the width of the signal line, its characteristic impedance is 20% higher than the characteristic impedance when the return path is infinitely wide.

43. If the return path width in the 50 ohm microstrip line is at least 3 times the signal line width, the deviation of its characteristic impedance from the characteristic impedance when the return path is infinitely wide is less than 1%.

44. The thickness of the wiring can affect the characteristic impedance. When the thickness is increased by 1MIL, the impedance will be reduced by 2 ohms.

45. The solder mask thickness of the fixed part of the microstrip line will reduce the characteristic impedance. The thickness will increase by 1MIL and the impedance will decrease by 2 ohms.

46. In order to obtain an accurate lumped circuit approximation, at least 3.5 LC sections are required in the spatial extension of each rise time.

47. The bandwidth of the single-cell LC model is 0.1/TD.

48. If the transmission line delay is shorter than 20% of the signal rise time, there is no need to terminate the transmission line.

49. In a 50 ohm system, the reflection coefficient caused by a 5 ohm impedance change is 5%.

50. Keep all sudden changes (IN) as short as possible than the magnitude of the rise time (NS).

51. The remote capacitive load will increase the rise time of the signal. 10-90 rise time is about (100xC)PS, where the unit of C is PF.

52. If the abrupt capacitance is less than 0.004XRT, it may not cause a problem.

53. The corner capacitance (Ff) of a 50 ohm transmission line is twice the line width (MIL).

54. Capacitive mutation will increase the 50% point delay by about 0.5XZ0XC.

55. If the abrupt inductance (NH) is less than 10 times the rise time (NS), no problem will occur.

56. For signals with a rise time of less than 1NS, the axial pin resistance with a loop inductance of about 10NH may produce more reflected noise. In this case, it can be replaced with a chip resistor.

57. In 50 ohm system, 4PF capacitor is needed to compensate 10NH inductance.

58. At 1GHZ, the resistance of 1 ounce copper wire is about 15 times its resistance in DC state.

59. At 1GHZ, the attenuation produced by the resistance of the 8MIL wide line is equivalent to the attenuation produced by the dielectric material, and the attenuation produced by the dielectric material changes faster with frequency.

60. For 3MIL or wider lines, the low-loss state all occurs at frequencies above 10MHZ. In the low loss state, the characteristic impedance and signal speed have nothing to do with loss and frequency. There is no dispersion phenomenon caused by loss in the common level interconnection.

61. The -3DB attenuation is equivalent to reducing the initial signal power to 50% and the initial voltage amplitude to 70%.

62. -20DB attenuation is equivalent to reducing the initial signal power to 1% and the initial voltage amplitude to 10%.

63. When in the skin effect state, the unit length of the signal path and the return path in series is approximately (8/W)Xsqrt(f) (where the line width is W: MIL; the frequency is F: GHZ).

64. In a 50 ohm transmission line, the attenuation per unit length produced by the conductor is about 36/(Wz0)DB/IN.

65. The dissipation factor of FR4 is about 0.02.

66. At 1GHZ, the attenuation produced by the dielectric material in FR4 is about 0.1DB/IN, and it increases linearly with frequency.

67. For the 8MIL wide, 50 ohm transmission line in FR4, the conductor loss is equal to the dielectric material loss at 1GHZ.

68. Restricted by the loss factor, the bandwidth of the FR4 interconnection line (the length of which is LEN) is about 30GHZ/LEN.

69. The shortest time that the FR4 interconnection line can propagate is 10PS/INxLEN.

70. If the interconnection line length (IN) is greater than 50 times the rise time (NS), the degradation of the rising edge caused by loss in the FR4 dielectric board cannot be ignored.

71. In a pair of 50 ohm microstrip transmission lines, when the line spacing is equal to the line width, the coupling capacitance between the signal lines accounts for about 5%.

72. In a pair of 50 ohm microstrip transmission lines, when the line spacing is equal to the line width, the coupling inductance between the signal lines accounts for about 15%.

73. For the rise time of 1NS, the saturation length of the near-end noise in FR4 is 6IN, which is proportional to the rise time.

74. The load capacitance of a line is a constant and has nothing to do with the proximity of other lines nearby.

75. For a 50 ohm microstrip line, when the line spacing is equal to the line width, the near-end crosstalk is about 5%.

76. For a 50 ohm microstrip line, when the line spacing is twice the line width, the near-end crosstalk is about 2%.

77. For a 50 ohm microstrip line, when the line spacing is 3 times the line width, the near-end crosstalk is about 1%.

78. For a 50 ohm strip line, when the line spacing is equal to the line width, the near-end crosstalk is about 6%.

79. For a 50 ohm strip line, when the line spacing is twice the line width, the near-end crosstalk is about 2%.

80. For a 50 ohm strip line, when the line spacing is 3 times the line width, the near-end crosstalk is about 0.5%.

81. In a pair of 50 ohm microstrip transmission lines, when the spacing is equal to the line width, the far-end noise is 4%Xtd/rt. If the line delay is 1ns and the rise time is 0.5ns, the far-end noise is 8%.

82. In a pair of 50 ohm microstrip transmission lines, when the spacing is twice the line width, the far-end noise is 2%Xtd/rt. If the line delay is 1ns and the rise time is 0.5ns, the far-end noise is 4%.

83. In a pair of 50 ohm microstrip transmission lines, when the spacing is 3 times the line width, the far-end noise is 1.5% Xtd/rt. If the line delay is 1ns and the rise time is 0.5ns, the far-end noise is 4%.

84. There is no far-end noise on the stripline or fully embedded microstrip line.

85. In a 50-ohm bus, whether it is a strip line or a microstrip line, to make the far-end noise in the most pregnant case less than 5%, the line spacing must be greater than twice the line width.

86. In a 50-ohm bus, when the distance between lines is equal to the line width, 75% of the interference on the victim line comes from the two adjacent lines on both sides of the victim line.

87. In a 50 ohm bus, when the distance between lines is equal to the line width, 95% of the interference on the victim line comes from two lines on each side of the victim line that are closest to each other.

88. In a 50-ohm bus, when the distance between lines is twice the line width, 100% of the interference on the victim line comes from the two adjacent lines on both sides of the victim line. This is to ignore the coupling with all other lines in the bus.

89. For surface wiring, increase the distance between adjacent signal lines to be enough to add a protective wiring, crosstalk will often be reduced to an acceptable level, and it is not necessary to increase protective wiring. Adding protective wiring with short-circuit terminals can reduce crosstalk to 50%.

90. For the strip line, the use of a protective line can reduce the crosstalk to 10% of that when the protective line is not used.

91. In order to keep the switching noise at an acceptable level, the mutual inductance must be less than 2.5nhx rise time (ns).

92. For connectors or packages limited by switching noise, the maximum usable clock frequency is 250MHZ/(NxLm). Among them, Lm is the mutual inductance between the signal/return path pair (nh), and N is the number of museums opened at the same time.

93. In the LVDS signal, the common mode signal component is more than 2 times that of the differential signal component.

94. If there is no coupling, the differential impedance of the differential pair is twice the impedance of any single-ended line.

95. For a pair of 50 ohm microstrip lines, as long as the voltage of one follower line remains high or low, the single-ended characteristic impedance of the other follower line is completely independent of the distance between adjacent lines.

96. In a tightly coupled differential microstrip line, compared with the coupling when the line width is equal to the line spacing, when the lines are far apart without coupling, the differential characteristic impedance will only be reduced by about 10%.

97. For wide-side coupled differential pairs, the distance between the lines should be at least larger than the line width. The purpose of this is to obtain an impedance of up to 100 ohms.

98. The FCC Class B requirement is that at 100MHZ, the far-field intensity at 3M should be less than 150UV/M.

99. Adjacent single-ended attack secondary lines produce 30% less differential signal crosstalk on a strongly coupled differential pair than on a weakly coupled differential pair.

100. The common mode signal crosstalk generated by the adjacent single-ended attack secondary line on the strongly coupled differential pair is 30% more than that on the weakly coupled differential pair.