High-speed signal routing basics in PCB Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is controlled impedance important in high-speed signal routing?

In high-speed PCB design, maintaining controlled impedance is crucial. What is the main reason for this?

A To simplify the routing process by ignoring signal timing

B To ensure signal integrity by minimizing reflections and signal loss

C To increase the power consumption of the circuit

D To reduce the physical size of the PCB

💡 Hint

Think about what happens when signals reflect back on a trace.

Controlled impedance helps keep signals clean by preventing reflections and losses, which can cause errors in data transmission.

❓ dax_lod_result

intermediate

Calculate the average trace length per layer

You have a dataset of PCB trace lengths per layer. Using DAX, which measure correctly calculates the average trace length per layer?

PCB Design

TraceLengthTable = DATATABLE("Layer", STRING, "Length_mm", DOUBLE, {{"Top", 120.5}, {"Bottom", 95.3}, {"Inner1", 110.0}, {"Inner2", 105.7}})

// Which measure is correct?

A AverageTraceLength = AVERAGE(TraceLengthTable[Length_mm])

B AverageTraceLength = AVERAGEX(VALUES(TraceLengthTable[Layer]), CALCULATE(SUM(TraceLengthTable[Length_mm])))

C AverageTraceLength = SUM(TraceLengthTable[Length_mm]) / COUNTROWS(TraceLengthTable)

D AverageTraceLength = CALCULATE(AVERAGE(TraceLengthTable[Length_mm]), ALL(TraceLengthTable))

💡 Hint

Think about the simplest way to get the average of a column.

AVERAGE directly calculates the mean of the Length_mm column. Other options either overcomplicate or produce incorrect results.

❓ visualization

advanced

Best visualization for signal integrity over multiple layers

You want to show how signal integrity varies across different PCB layers and trace lengths. Which visualization is best?

A Stacked bar chart showing signal integrity score per layer

B Line chart with layers on the x-axis and signal integrity on the y-axis

C Scatter plot with trace length on x-axis and signal integrity on y-axis, colored by layer

D Pie chart showing percentage of signal integrity issues per layer

💡 Hint

Consider how to show relationships between two numeric variables and a category.

A scatter plot lets you see how trace length relates to signal integrity and how layers differ by color, giving a clear multi-dimensional view.

🔧 Formula Fix

advanced

Identify the error in this DAX measure for total signal delay

Given the DAX measure below, what is the error?

TotalSignalDelay = SUMX(SignalTable, SignalTable[Length_mm] * SignalTable[Delay_ns])

A The measure is correct and will calculate total delay properly

B SUMX cannot multiply two columns directly; a calculated column is needed first

C SignalTable[Delay_ns] should be wrapped in CALCULATE() inside SUMX

D SUMX requires a table expression, but SignalTable is a column reference

💡 Hint

Recall how SUMX works with tables and row context.

SUMX iterates over the table SignalTable, multiplying Length_mm by Delay_ns for each row, then sums the results. This is valid syntax and logic.

🎯 Scenario

expert

Optimizing PCB layer stack for minimal crosstalk

You have a 6-layer PCB with high-speed signals on layers 2 and 5. To minimize crosstalk, which layer stack arrangement is best?

A Alternate signal and power planes without ground planes to reduce interference

B Place power planes adjacent to signal layers 2 and 5, with ground planes in the middle layers

C Place all signal layers consecutively in the middle, with ground and power planes on outer layers

D Place ground planes adjacent to signal layers 2 and 5, with power planes in the middle layers

💡 Hint

Think about how ground planes help shield signals and reduce noise.

Ground planes next to signal layers provide a return path and shield signals, reducing crosstalk and noise effectively.