How to Measure Impedance Mismatch Of Active Devices

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Measuring impedance mismatch under hot time-domain reflectometry

Impedance mismatch characterization in a high-speed digital application design and test requires understanding the reflection signals in both the time and frequency domain. The eye diagram is a crucial measurement parameter in the time domain. If the transmitter lacks impedance matching, the signal reflects into the channel, causing eye closure in the diagram when it reaches the receiver. This reflection magnitude can be quantified in the frequency domain through return loss measurements. Given that device characteristics can vary between power-on and power-off states, it is essential to evaluate devices under conditions resembling actual operation.

An advanced network analyzer with enhanced time domain analysis capabilities enables hot time-domain reflectometry (TDR) and hot return loss measurements to be performed with the power-on state. When testing a transmitter in a high-speed digital application, the biggest issue is that the transmitter output signal produces spurious noise. Using a narrow-band receiver in the network analyzer can help mitigate this issue, while the right circuitry within the network analyzer is crucial to protect against an electrostatic discharge (ESD).

Impedance mismatch measurement solution

Measuring the impedance mismatch requires a network analyzer that can offer hot TDR and hot return loss measurements in enhanced time domain analysis software. The Keysight ENA network analyzer is a compact, two-port, USB-connected vector network analyzer with a frequency range from 100 kHz up to 53 GHz. It enables complete device characterization for passive components, amplifiers, mixers, and frequency converters. Combined with the time domain measurement software, the instrument offers ESD protection with a proprietary chip that enables easy measurement and evaluation in both the frequency and time domain.

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