Time Domain Reflectometry (TDR) and S-parameter Measurements

Closing the gap for simple S-parameter measurements: the DSA8200 vs. the VNA. Watch the video 
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TDR

Time Domain Reflectometry (TDR) is a convenient way to evaluate impedance values and variations along a transmission line such as cables, connectors or a microstrip on a PC board. At speeds of less than 1Gbps, transmission quality can be analyzed in time domain just as the signal integrity of data signals is often analyzed in time domain. Impedance tolerances are contained in the electrical specifications for many of today's digital system components, such as Rambus, USB, Firewire, and many more. If these tolerances are violated, signal integrity issues become apparent.

S-parameters

At speeds of 1Gbps and beyond, frequency domain performance of the interconnect using S-parameters needs to be evaluated as well, which can be easily and efficiently performed using IConnect® software. IConnect employs simplified frequency domain calibration procedures, which provide frequency domain dynamic range suitable for serial data S-parameter measurements, and results in a much faster throughput for S-parameter measurements both in R&D and in manufacturing applications. Fixture-based S-parameter measurements, as required by many serial data standards, using IConnect are also very easy, since IConnect calibration makes fixture de-embedding a simple measurement step.

In addition to impedance and S-parameters measurements, in today's environment, engineers also use modeling tools to design these high-speed circuits. Measurement-based Spice modeling ensures the accuracy of the model by design, since it is compared to measurements and verified as part of the modeling process. Modification can be done easily to correct any characterization issues.

Studies from Intel and Samtec on the correlation between VNAs and TDR-generated S-parameter measurements

• Correlation between VNA and TDR/TDT Extracted S-Parameters (491 kB)
  (Cherry Wakayama, Jeff Loyer) - The purpose of this paper is to validate the use of the IConnect® software in generating these parameters as an alternative to the more widely accepted VNA generated data.
• Comparison of Vector Network Analyzer and IConnect® Generated S-Parameters (161 kB)
  (Kieran Kelly - Samtec, Inc.) - The paper presents the results of comparative analysis done by Samtec between the S-parameters generated by a VNA vs. the S-parameters generated by IConnect.