IEC 62783-1-2:2025

Overview - IEC 62783-1-2:2025 (Twinax cables, Time‑domain Impedance)

IEC 62783-1-2:2025 specifies a time‑domain test method for measuring impedance of twinax cables and twinax cable assemblies used in digital communications. The standard defines different time‑domain impedance types (differential, common‑mode, odd‑mode, even‑mode), explains the principle of time‑domain reflectometry (TDR) measurement, and sets out the measurement, calibration and reporting requirements for accurate time‑domain impedance characterization.

Key topics and technical requirements

• Impedance definitions: Clear definitions of reflection coefficient (ρ), differential‑mode and common‑mode impedance, and the single‑ended odd/even mode characteristic impedances used in balanced pair testing.
• Measurement principle: Differential TDR principles - launching step signals (differential or common‑mode) and observing incident and reflected waves to determine impedance and locate discontinuities.
• Test methods and equipment: Requirements for test equipment and accessories, including step generators, wide‑band receivers (oscilloscopes), and options for using modern VNAs with IFFT for time‑domain analysis.
• Calibration procedures: Two calibration approaches are covered (coaxial calibration kits and air‑line/standard termination methods) to ensure traceable impedance measurement.
• Practical measurement parameters: Guidance on system rise/fall time, device‑under‑test (DUT) length, propagation delay/velocity calculations for distance localization, and techniques to distinguish resistive/inductive/capacitive discontinuities.
• Reporting and requirements: Minimum test report content and pass/fail or measurement requirement criteria (see Clause 7–8 for details).
• Normative references: Integrates requirements from IEC 62783-1 (generic specification) and IEC 62783-1-1 (general time‑domain test requirements).

Applications and who uses it

• Cable and connector manufacturers: For product qualification, batch testing, and design verification of twinax cables used in high‑speed data links.
• Test laboratories and compliance engineers: For standardized TDR measurements, calibration, and reproducible reporting of impedance characteristics.
• System integrators and PCB designers: To locate and diagnose impedance discontinuities in short‑reach, high‑frequency interconnects (connectors, cable assemblies, PCB traces).
• R&D and QA teams: To optimize differential and common‑mode behavior, improve signal integrity, and support fault localization.

Keywords: IEC 62783-1-2, twinax cables, time domain, impedance, TDR, differential impedance, odd‑mode, even‑mode, common‑mode, time domain reflectometry, calibration, vector network analyzer.

Related standards

• IEC 62783-1:2023 - Twinax cables for digital communications - Part 1: Generic specification
• IEC 62783-1-1:2022 - Twinax cables for digital communications - Part 1-1: Time‑domain test methods - General requirements