Circuit Technology Services Provides TDR Impedance Testing for PCB Signal Integrity Analysis

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Circuit Technology Services Inc., a provider of PCB testing, analysis and rework services for the electronics manufacturing industry, provides TDR impedance testing to help identify PCB impedance issues that can affect performance and reliability. The company states that more PCBs require impedance testing to ensure proper signal function.

Controlled Impedance

Circuit Technology Services explains that signal integrity in PCBs becomes increasingly important as clock speeds and data rates increase. At high speeds, PCB traces act as transmission lines and electrical energy can reflect back and forth. Controlled impedance traces are designed to minimize electrical reflections and support signal transmission throughout the PCB.

The company states that PCB designers typically attempt to match the characteristic impedance of the signal traces to the actual load the trace will receive when the PCB functions in a working system to maximize signal transfer.

Uncontrolled Impedance

When there is a mismatch between characteristic or inherent impedance and working impedance, signal loss and reflection can occur, resulting in reduced signal quality, including low gain, noise and random errors. The company compares this to impedance mismatch between a television antenna and coax cable, which can result in poor television picture quality and multiple images due to reflection.

Time Domain Reflectometry (TDR) Test

Circuit Technology Services uses Time Domain Reflectometry (TDR) testing to verify PCB impedance. The TDR test applies a fast electrical step signal to the PCB or coupon through a controlled impedance cable and probe. When impedance values change, part of the signal power is reflected back to the TDR tester.

The company records and graphs the data to display impedance values over the distance of the PCB or coupon under test. Data including average, standard deviation, minimum and maximum values are also displayed.

Circuit Technology Services provides TDR impedance testing with capabilities including:

• 0-150 Ohms
• Single and differential readings
• Coupons and PCBs
• 1% tolerance at 50 ohms
• Bandwidth up to 7 gigahertz
• Comprehensive graphs and reports
• Risetime of 70 picoseconds

Click here to learn more about the TDR impedance testing.