Meaning
An electrical characterization method utilizes fast-rise-time voltage steps to measure the characteristic impedance profile of a transmission line. This diagnostic procedure, called tdr testing, evaluates the reflected waveform returned from the trace to determine the location and magnitude of impedance mismatches. It is widely used during board fabrication and assembly to verify that high-speed signal lines comply with specified trace geometry, ensuring reliable signal propagation at gigabit frequencies.
Impedance Measurement
Launching a step stimulus into the trace reveals the instantaneous impedance at every point along its length. During tdr testing, the amplitude of the reflected signal indicates whether the trace is too narrow, too wide or suffers from manufacturing defects such as copper voids. This measurement helps confirm that the circuit board conforms to the high-frequency design specifications.
Fault Localization
Pinpointing the exact position of a broken trace or short circuit is made possible by calculating the time delay of the returned signal. With tdr testing, engineers can isolate physical damages inside multi-layer structures without resorting to destructive cross-sectioning. This non-destructive diagnostic speed accelerates failure analysis during product development.
Calibration Verification
Accuracy depends on compensating for the loss in the test cables and probes. Using reference standards before running tdr testing establishes a reliable baseline. This step minimizes measurement errors across different test locations.
