- 7.1 Forget the Word Ground
- 7.2 The Signal
- 7.3 Uniform Transmission Lines
- 7.4 The Speed of Electrons in Copper
- 7.5 The Speed of a Signal in a Transmission Line
- 7.6 Spatial Extent of the Leading Edge
- 7.7 “Be the Signal”
- 7.8 The Instantaneous Impedance of a Transmission Line
- 7.9 Characteristic Impedance and Controlled Impedance
- 7.10 Famous Characteristic Impedances
- 7.11 The Impedance of a Transmission Line
- 7.12 Driving a Transmission Line
- 7.13 Return Paths
- 7.14 When Return Paths Switch Reference Planes
- 7.15 A First-Order Model of a Transmission Line
- 7.16 Calculating Characteristic Impedance with Approximations
- 7.17 Calculating the Characteristic Impedance with a 2D Field Solver
- 7.18 An n-Section Lumped-Circuit Model
- 7.19 Frequency Variation of the Characteristic Impedance
- 7.20 The Bottom Line
- End-of-Chapter Review Questions

## End-of-Chapter Review Questions

The answers to the following review questions can be found in Appendix D, “Review Questions and Answers.”

**7.1**What is a real transmission line?**7.2**How is an ideal transmission line model different from an ideal R, L, or C model?**7.3**What is ground? Why is it a confusing word for signal integrity applications?**7.4**What is the difference between chassis and earth ground?**7.5**What is the difference between the voltage on a line and the signal on a line?**7.6**What is a uniform transmission line, and why is this the preferred interconnect design?**7.7**How fast do electrons travel in a wire?**7.8**What is the difference between conduction current, polarization current, and displacement current?**7.9**What is a good rule of thumb for the speed of a signal on an interconnect?**7.10**What is a good rule of thumb for the aspect ratio of a 50-Ohm microstrip?**7.11**What is a good rule of thumb for the aspect ratio of a 50-Ohm stripline?**7.12**What is the effect called when the dielectric constant and the speed of a signal are frequency dependent?**7.13**What are two possible reasons the characteristic impedance of a transmission line would be frequency dependent?**7.14**What is the difference between the instantaneous impedance and the characteristic impedance and the input impedance of a transmission line?**7.15**What happens to the time delay of a transmission line if the length of the line increases by 3x?**7.16**What is the wiring delay of a transmission line in FR4?**7.17**If the line width of a transmission line increases, what happens to the instantaneous impedance?**7.18**If the length of a transmission line increases, what happens to the instantaneous impedance in the middle of the line?**7.19**Why is the characteristic impedance of a transmission line inversely proportional to the capacitance per length?**7.20**What is the capacitance per length of a 50-Ohm transmission line in FR4? What happens to this capacitance per length if the impedance doubles?**7.21**What is the inductance per length of a 50-Ohm transmission line in FR4? What if the impedance doubles?**7.22**What can you say about the capacitance per length of an RG59 cable compared to an RG58 cable?**7.23**What do we mean when we refer to “the impedance” of a transmission line?**7.24**A TDR can measure the input impedance of a transmission line in a fraction of a nanosecond. What would it measure for a 50-Ohm transmission line, open at the end, that is 2 nsec long? What would it measure after 5 seconds?**7.25**A driver has a 10-Ohm output resistance. If its open circuit output voltage is 1 V, what voltage is launched into a 65-Ohm transmission line?**7.26**What three design features could be engineered to reduce the impedance of the return path when a signal changes return path planes?**7.27**Which is a better starting model to use to describe an interconnect up to 100 MHz: an ideal transmission line, or a 2-section LC network?**7.28**An interconnect on a board is 18 inches long. What is an estimate of the time delay of this transmission line?**7.29**In a 50-Ohm microstrip, the line width is 5 mils. What is the approximate dielectric thickness?**7.30**In a 50-Ohm stripline, the line width is 5 mils. What is the length of the transmission line?