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Optically coupled electrical sampling system with 4‐GHz bandwidth

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3 Author(s)
Samaan, S.B. ; Tektronix Inc., M/S 50‐276, P. O. Box 500, Beaverton, Oregon 97077 ; Pearson, L.Wilson ; Smith, Charles E.

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A new approach to the design of a fiber‐optic interface that links a commercial sampling head to its matching time‐domain reflectometer (TDR)/sampler oscilloscope plug‐in unit is reported. Three fiber‐optic links replace the wired signal paths of the original design that convey the vertical error signal, the feedback signal, and the horizontal sampling command signal between the sampling head and the oscilloscope sampling plug‐in. The dielectric fiber pigtails allow the use of the sampling head inside objects that need to be electromagnetically insulated from the instrumentation system. Low‐frequency analog links are used to convey the error and feedback signals. The sampling command signal is conveyed via a link where a powerful, fast‐rise infrared laser pulse is generated. The laser pulse is used to trigger an avalanche transistor in the strobe generator circuit of the sampling head by directly coupling the optical energy to the transistor chip. This direct method of detection minimizes the time jitter introduced to the strobe signal, resulting in a bandwidth of 4 GHz. Some of the results of the tests which were carried out on the system are reported.

Published in:

Review of Scientific Instruments  (Volume:58 ,  Issue: 1 )