Simulations and measurements show consistency
By Martin Rowe, Senior Technical Editor -- Test & Measurement World, 11/1/2007
Engineers often use both eye diagrams and S-parameters to characterize passive components such as connectors, printed-circuit board (PCB) backplanes, and relays. When engineers Minh Tran and An Trinh of Teledyne Relays wanted to characterize a new design, they worked with customers to verify that both methods could produce the same results. They also showed that different instruments could produce similar results.
| Download the paper by Minh Tran and An Trinh. |
Tran and Trinh measured s 21 on relays in their lab with an Agilent Technologies vector-network analyzer (VNA). They sent their test results to a customer, whose engineers produced a simulated eye diagram from a simulated 29–1 pseudorandom bit sequence (PRBS) signal at 10 Gbps. The customer's engineers repeated the s 21 measurements on an Anritsu VNA and ran the results through the same algorithm, which produced nearly identical results.
The customer's engineers then set out to prove the validity of the simulated eye diagrams by making the measurements directly with an Agilent sampling oscilloscope. The results proved that the s 21-based simulations were valid.
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| The eye diagram on the left was made from s21 measurements on a VNA. The eye on the right was measured with a sampling oscilloscope. Courtesy of Teledyne Relays. |
Not content to stop there, Tran and Trinh approached another customer to measure s 21. This customer used an Agilent VNA and also produced a simulated eye diagram. The measurements proved consistent with those produced by the first customer.
In addition to proving the validity of the s 21 measurements, Tran and Trinh measured the effects that a test board and cables had on the eye diagrams. They also measured insertion loss of the relays at frequencies up to 21 GHz with the Agilent VNA. The test setup used impedance-matched transmission lines between the relays and the VNA. Test results shows a nearly flat response at frequencies up to 19.5 GHz.
