S-4

Template:Plugin Sidebar 2 The Tektronix S-4 is a sampling head for 7000- and 3S-series samplers. It was designed by George Frye and introduced in 1968. It is the fastest of the S-series plug-in samplers.

Key Specifications

Rise time	25 ps (observed with S-50 or S-52, 35 ps)
Bandwidth	14.5 GHz
Input impedance	50 Ω (terminated SMA connector)
Input range	1 Vp-p (operating)
Maximum input	±5 V max. non-destructive
Noise	< 5 mV
Features	trigger signal pick-off for internal triggering

Internals

The S-4 sampling gate is based upon a traveling wave trapped-charge transmission line in which the sampling window is set by the propagation time of a pulse edge through a thick-film transmission line. This technique requires only a sharp pulse edge rather than a precise pulse width, which is harder to generate. The sampling diodes are housed in a special coaxial connector that provides a high bandwidth signal path.

To disassemble the sampler hybrid, first remove it from the sampler board as per the manual. Remove the input connector using a 7/32" wrench and remove the 20 dB attenuator with small pliers. The ceramic board is held to the housing using roll pins that can be pressed out with a 0.030" pin punch. The hybrid has six diodes, each about 0.75mm square. The cathodes are glued to the gold substrate with conductive epoxy and the anodes are wire-bonded (twice) over a gap to the next step in the strobe line. It appears that a standard beam-lead diode may fit across the gap but cleanly removing a failed diode without damaging the substrate would be quite difficult.

Links

• S-4 page @ amplifier.cd
• James R. Andrews, Comparison of Ultra-Fast Rise Sampling Oscilloscopes. Picosecond Pulse Labs App Note AN-2a, 1989

Pictures

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  Top view of the S4 plug-in

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  Left view

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  Right view

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  Schematic

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  Sampler board, strobe side

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  Sampler board, preamp side

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  Sampler board, disassembled with parts orientation

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  Microphotograph of sampler hybrid

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  S-4 in 7S11

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  S-4 in 7S11