Power integrity basics in PCB Design - Real Business Scenario

Scenario Mode

👤 Your Role: You are a PCB design engineer working on a new electronic device.

📋 Request: Your manager wants you to analyze the power integrity of the PCB to ensure stable voltage supply and minimize noise.

📊 Data: You have voltage measurements at various test points on the PCB under different load conditions, along with timestamps and load current values.

🎯 Deliverable: Create a report with charts showing voltage stability over time, identify any voltage drops or noise spikes, and provide recommendations to improve power integrity.

Sample Data

Timestamp	Test Point	Voltage (V)	Load Current (A)
10:00	TP1	3.3	0.5
10:00	TP2	3.28	0.5
10:05	TP1	3.25	1.0
10:05	TP2	3.22	1.0
10:10	TP1	3.20	1.5
10:10	TP2	3.18	1.5
10:15	TP1	3.15	2.0
10:15	TP2	3.10	2.0
10:20	TP1	3.12	2.5
10:20	TP2	3.08	2.5

1

Step 1: Load the data into your BI tool and create a table visualization showing Timestamp, Test Point, Voltage, and Load Current.

Use the raw data as is for initial inspection.

Expected Result

A table showing all voltage readings at each test point over time with corresponding load currents.

2

Step 2: Create a line chart with Timestamp on the X-axis and Voltage on the Y-axis. Use Test Point as the legend to show separate lines for TP1 and TP2.

Configure line chart: X=Timestamp, Y=Voltage, Legend=Test Point.

Expected Result

A line chart showing voltage trends over time for TP1 and TP2.

3

Step 3: Add Load Current as a secondary Y-axis on the same chart to see how voltage changes relate to load current.

Configure secondary Y-axis for Load Current with same X-axis (Timestamp).

Expected Result

Combined chart showing voltage drop and load current increase over time.

4

Step 4: Calculate the voltage drop at each test point by subtracting the minimum voltage from the maximum voltage over the time period.

Create measure: Voltage Drop = MAX(Voltage) - MIN(Voltage) grouped by Test Point.

Expected Result

Voltage Drop for TP1 = 3.3 - 3.12 = 0.18 V; for TP2 = 3.28 - 3.08 = 0.20 V.

5

Step 5: Create a bar chart showing voltage drop for each test point.

Configure bar chart: X=Test Point, Y=Voltage Drop measure.

Expected Result

Bar chart showing TP2 has slightly higher voltage drop than TP1.

6

Step 6: Identify any noise spikes by calculating the difference between consecutive voltage readings at each test point.

Create measure: Voltage Change = Voltage at current timestamp - Voltage at previous timestamp, grouped by Test Point.

Expected Result

Voltage changes mostly small except a slight drop at 10:15 for TP2.

7

Step 7: Create a scatter plot with Timestamp on X-axis and Voltage Change on Y-axis, with Test Point as legend.

Configure scatter plot: X=Timestamp, Y=Voltage Change, Legend=Test Point.

Expected Result

Scatter plot showing voltage change spikes over time for each test point.

8

Step 8: Summarize findings in a report: voltage drops increase with load current, TP2 shows slightly worse power integrity, and minor noise spikes occur at higher loads.

Write summary text based on visualizations and calculations.

Expected Result

Clear report explaining voltage stability issues and recommendations.

Final Result

Power Integrity Report

Timestamp  | TP1 Voltage | TP2 Voltage | Load Current
-----------------------------------------------------
10:00     | 3.3 V       | 3.28 V      | 0.5 A
10:05     | 3.25 V      | 3.22 V      | 1.0 A
10:10     | 3.20 V      | 3.18 V      | 1.5 A
10:15     | 3.15 V      | 3.10 V      | 2.0 A
10:20     | 3.12 V      | 3.08 V      | 2.5 A

Voltage Drop (V): TP1=0.18, TP2=0.20

Observations:
- Voltage decreases as load current increases.
- TP2 has slightly higher voltage drop than TP1.
- Minor voltage noise spikes detected at 10:15.

Recommendations:
- Improve power delivery network at TP2.
- Add decoupling capacitors to reduce noise.
- Monitor voltage under peak loads.

✓Voltage at both test points drops as load current increases.

✓Test Point 2 (TP2) experiences a slightly higher voltage drop than TP1.

✓Small voltage noise spikes appear at higher load currents, especially around 10:15.

✓Improving power delivery and adding noise reduction components can enhance power integrity.

Bonus Challenge

Create a DAX measure or equivalent formula to calculate the average voltage for each test point during load currents above 1.5 A.

Show Hint

Filter the data where Load Current > 1.5 A, then calculate the average Voltage grouped by Test Point.

Practice

1. What is the main goal of power integrity in PCB design?

easy

A. To reduce the size of the PCB

B. To increase the speed of the PCB signals

C. To ensure clean and stable power supply to electronic components

D. To improve the color of the PCB silkscreen

Solution

1. Step 1: Understand power integrity concept

   Power integrity focuses on providing clean and stable power to electronic parts.

2. Step 2: Compare options with the concept

   Only To ensure clean and stable power supply to electronic components matches the goal of power integrity; others relate to different PCB aspects.

3. Final Answer:

   To ensure clean and stable power supply to electronic components -> Option C

4. Quick Check:

   Power integrity = stable power [OK]

Hint: Power integrity means stable power, not speed or size [OK]

Common Mistakes:

• Confusing power integrity with signal speed
• Thinking power integrity affects PCB size
• Mixing power integrity with PCB appearance

2. Which of the following is the correct way to describe a decoupling capacitor in power integrity?

easy

A. A component that stores data temporarily

B. A device that filters noise from the power supply

C. A resistor that limits current flow

D. A connector for external power

Solution

1. Step 1: Define decoupling capacitor role

   It filters out noise and stabilizes voltage in power lines.

2. Step 2: Match options to definition

   A device that filters noise from the power supply correctly describes the noise filtering function; others describe unrelated parts.

3. Final Answer:

   A device that filters noise from the power supply -> Option B

4. Quick Check:

   Decoupling capacitor = noise filter [OK]

Hint: Decoupling capacitors filter noise, not store data [OK]

Common Mistakes:

• Confusing capacitors with resistors
• Thinking capacitors store data like memory
• Mixing connectors with capacitors

3. Given a PCB power supply with a sudden current spike, what is the expected effect on the voltage if no power integrity measures are applied?

medium

A. Voltage will drop causing potential device errors

B. Voltage will remain perfectly stable

C. Voltage will increase steadily

D. Voltage will oscillate randomly without pattern

Solution

1. Step 1: Understand current spike impact

   A sudden current spike can cause voltage drop if power integrity is poor.

2. Step 2: Analyze options for voltage behavior

   Voltage will drop causing potential device errors correctly states voltage drop causing errors; others are incorrect or unlikely.

3. Final Answer:

   Voltage will drop causing potential device errors -> Option A

4. Quick Check:

   Current spike without integrity = voltage drop [OK]

Hint: Current spikes cause voltage drops without protection [OK]

Common Mistakes:

• Assuming voltage always stays stable
• Thinking voltage rises with current spike
• Believing voltage oscillates randomly

4. A PCB designer notices noise on the power line causing device resets. Which of these fixes is most likely to solve the problem?

medium

A. Use thinner copper layers on the PCB

B. Increase the trace length of the power line

C. Remove all capacitors from the power line

D. Add more decoupling capacitors near the device

Solution

1. Step 1: Identify cause of noise and resets

   Noise on power lines can cause device resets due to unstable voltage.

2. Step 2: Evaluate fixes for noise reduction

   Adding decoupling capacitors near devices reduces noise; other options worsen or ignore the issue.

3. Final Answer:

   Add more decoupling capacitors near the device -> Option D

4. Quick Check:

   Decoupling capacitors reduce noise [OK]

Hint: Add capacitors close to devices to fix noise [OK]

Common Mistakes:

• Increasing trace length increases noise
• Removing capacitors removes noise filtering
• Thinner copper increases resistance and noise

5. In a complex PCB design, how can simulation tools help improve power integrity before manufacturing?

hard

A. By predicting voltage drops and noise to optimize capacitor placement

B. By automatically routing all signal traces

C. By increasing the PCB size to reduce noise

D. By changing component values without user input

Solution

1. Step 1: Understand simulation tool purpose

   Simulation tools analyze power quality issues like voltage drops and noise.

2. Step 2: Match tool benefits to options

   By predicting voltage drops and noise to optimize capacitor placement correctly describes using simulation to optimize capacitor placement and power integrity.

3. Final Answer:

   By predicting voltage drops and noise to optimize capacitor placement -> Option A

4. Quick Check:

   Simulation predicts power issues for fixes [OK]

Hint: Simulate to find and fix power issues early [OK]

Common Mistakes:

• Thinking simulation auto-routes signals
• Assuming simulation changes PCB size
• Believing simulation changes components without input