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.
|Rise time||25 ps (observed with S-50 or S-52, 35 ps)|
|Input impedance||50 Ω (terminated SMA connector)|
|Input range||1 Vp-p (operating)|
|Maximum input||±5 V max. non-destructive|
|Noise||< 5 mV|
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.
1979: $1,435 (~$5,600 in 2022 Dollars)
According to an internal memo, in 1979 annual sales were estimated at 150 units.
- S-4 page @ amplifier.cd
- James R. Andrews, Comparison of Ultra-Fast Rise Sampling Oscilloscopes. Picosecond Pulse Labs App Note AN-2a, 1989