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).
Additional resources for measuring impedance mismatch
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