S-4
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.
During the development of the S-4, the velocity gate theory was tested using a length of transmission line between diodes. This led to a aperture time that depended upon twice the propagation delay of the length of transmission line.
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 |
|
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.
Prices
1979: $1,435 (~$5,600 in 2022 Dollars)
According to an internal memo, in 1979 annual sales were estimated at 150 units.
