In high-speed digital circuit debugging, many engineers utilize eye diagram analysis to assess signal integrity. By capturing eye diagrams with an oscilloscope, engineers can intuitively evaluate key metrics such as inter-symbol interference and noise margin. This article discusses the setup of eye diagrams using mainstream oscilloscopes like Tektronix.
1. Hardware Connection and Basic Setup
① Probe Configuration
Use a differential probe with a bandwidth of over 1GHz, connecting the signal output of the device under test to oscilloscope channel 1.
Use a spring ground lead connection, keeping the length within 3cm to reduce loop interference.
② Trigger System Configuration
Trigger Mode: Select “Pattern Trigger” or “Sequence Trigger”.
Trigger Level: Set within the 45%-55% range of the signal amplitude.
Trigger Position: Adjust the horizontal time base to achieve a pre-trigger depth of 30%.
③ Time Base and Sampling Rate
Sampling Rate: ≥2 times the signal baud rate (for example, testing a 5Gbps signal requires a sampling rate of 10GSa/s).
Storage Depth: Enable “Deep Storage Mode” to ensure capturing data over 100,000 unit intervals (UI).
2. Eye Diagram Generation/Settings
① Clock Recovery Configuration
Recovery Method:
Constant Frequency Mode: Suitable for fixed pattern signals like NRZ.
Phase-Locked Loop Mode: Select a second-order phase-locked loop with a damping factor set to 0.707.
Reference Clock: Preferably use the embedded clock within the signal; external clock error must be controlled within ±50ppm.
② Eye Diagram Overlay Parameters
Overlay Count: Set to ≥1000 overlays, using color temperature mode to enhance depth perception.
Mask Testing: Load standard templates such as PCIe Gen5/USB4 and enable real-time violation detection.
③ Advanced Measurement Options
Eye Height Measurement: Measure the vertical amplitude in the central 20% UI area of the eye diagram.
Eye Width Measurement: Measure the time span within ±5% UI range at the crossing points of the eye diagram.
Jitter Decomposition: Enable RJ/DJ separation algorithm, setting histogram bar width ≤2ps.
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