Summary of Every PCB Designer Needs To Know This About PCB Track Impedance | TDR | Eric Bogatin

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00:00:00 - 01:00:00

This video explains impedance in PCB design and how to measure it using a TDR. The author warns against connecting the TDR to the output of the circuit, as this could cause damage.

  • 00:00:00 This video explains impedance in PCB design, and how understanding it can help you do better PCB layout and design. Eric Bogatin discusses ddr (distortion-dissipation ratio) and how it helps measure the impedance of a transmission line. Characteristic impedance is one value of impedance that characterizes a transmission line, and is what we care about when engineering interconnects. By keeping the impedance constant, we can ensure that reflections do not occur, and transmit signals more reliably.
  • 00:05:00 When designing PCB tracks, it is important to keep in mind the impedance of the signal traveling on them. If the impedance of the track is too high, reflections can cause distortion and interference.
  • 00:10:00 PCB track impedance is really high and can cause reflections at the source and receiver, which can ruin your day if not managed. The target impedance for PCB track impedance is a trade-off of many factors, including device technology and power consumption. 50 ohms is a good balance for most scenarios.
  • 00:15:00 This YouTube video provides an overview of the characteristics of a PCB track's impedance. It explains that a 50 ohm impedance is a reasonable compromise for most circuits, and that there are trade-offs involved when choosing an impedance for a PCB. The video also mentions that noise levels can be reduced by closer proximity of the return plane to the signal lines.
  • 00:20:00 This video discusses the importance of knowing the impedance of PCB tracks, and how a 50 ohm impedance is a good starting point for designers. It goes on to say that Intel parameterized a bus using a variable line width and dielectric thickness and spacing, and used a variable dielectric constant, variable length, and different impedances for the receiver and transmitter. 400,000 monte carlo simulations were conducted to determine the most important terms. They found that the line width and dielectric thickness and spacing were the most important terms, and that a via with an impedance of 85 ohms was a better match to the impedance of vias.
  • 00:25:00 The video discusses the trade-off between tightly coupling differential pairs versus loosely coupling them. It argues that, strictly speaking, differential impedance between the n and p lines is the same regardless of the distance between the traces. The video concludes with a mention of a upcoming technical workshop on using Altium's built-in 2D field solver to calculate differential and single-ended impedance.
  • 00:30:00 PCB designers need to know that the differential impedance of tracks is the same no matter the coupling. Tightly coupled transmission lines produce the highest interconnect density possible, while wider lines sacrifice conductor loss for impedance. If the loss is more important to the designer than interconnect density, then a wide line is the best option.
  • 00:35:00 The video discusses how PCB track impedance is important and how a tdr can be used to measure it. The author explains how the impedance of the cable entering the transmission line has been calibrated out, and then shows a simulation of a waveform travelling down a transmission line.
  • 00:40:00 The video demonstrates the use of the TDR to identify the impedance line and reflections in a transmission line. The video also provides an example of how to use a low impedance driver and a high impedance receiver to create ringing.
  • 00:45:00 The TDR helps PCB designers estimate the instantaneous impedance of a signal source. PCB designers use the TDR to see reflections of discontinuities in the electrical environment. This information helps PCB designers understand how the signal sees the electrical environment and makes corrections to the design of the cable to ensure a uniform line is seen in the reflection.
  • 00:50:00 This video explains how PCB track impedance affects the signal sent down a cable. It also shows how to measure the impedance of a cable. Finally, it demonstrates how to connect two components and measure the signal.
  • 00:55:00 The author discusses the importance of impedance in PCB design, and explains how to measure it using a TDR. He also warns against connecting the TDR to the output of the circuit, as this could cause damage.

01:00:00 - 01:25:00

The TDR is a tool used to measure the electrical environment a signal sees, and is particularly useful for identifying discontinuities in a circuit. This video explains how to use a TDR to measure the impedance of PCB tracks. This is important for verifying the impedance of PCB lines and for designing systems that meet performance requirements.

  • 01:00:00 The TDR is a tool used to measure the electrical environment a signal sees, and is particularly useful for identifying discontinuities in a circuit.
  • 01:05:00 This video explains how PCB track impedance can be evaluated using a scope and 3D field solver. The impedance profile of the interconnect can be seen as a discontinuity in the received signal.
  • 01:10:00 This video explains how TDRS (time-domain reflectometry) can be used to identify problems with cable connections, such as broken clocks. TDRS can also be used to determine the characteristic impedance of a cable.
  • 01:15:00 This video explains how to use a TDR to measure the impedance of PCB tracks. This is important for verifying the impedance of PCB lines and for designing systems that meet performance requirements.
  • 01:20:00 PCB track impedance is important to consider when designing a PCB, especially for high-speed applications. Minimizing stubs and non-functional pads in vias can improve impedance. While 10 gigabits per second is in volume production, optimizing the design of vias at higher frequencies is still necessary.
  • 01:25:00 PCB designers should be aware of the Track Impedance (TDR) test and how it can be used to check the performance of their designs. The test measures the impedance of a PCB track and can be used to diagnose problems with the track and the circuit it connects to.

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