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


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.

During the development of the S-4, the velocity gate theory was tested using a length of transmission line between diodes. This led to an aperture time that depended upon twice the propagation delay of the length of transmission line.

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 0.75 mm². 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 (~$6,000 in 2023 dollars)

According to an internal memo, annual sales were estimated at 150 units in 1979.


Documents Referencing S-4

Document Class Title Authors Year Links
Service Scope 53 Dec 1968.pdf Article Digital Systems Come Of Age John Bowne 1968
Service scope dec 1968 ocr.pdf Article Digital Systems Come of Age John Bowne 1968
Service Scope 52 Oct 1968.pdf Article The State of the Art in Sampling Al Zimmerman 1968
Service Scope 52 Oct 1968.pdf Article A New Approach to Fast Gate Design George Frye 1968
42W-5850.pdf Application Note Preventing Sampling Head Overdrive and Static Damage Gary Mott 1985

Patents that may apply to S-4

Page Title Inventors Filing date Grant date Links
Patent US 3629731A Sampling system George Frye 1968-07-12 1971-12-21



Some Parts Used in the S-4

Part Part Number(s) Class Description Used in
152-0335-00 152-0335-00 Discrete component step recovery diode S-4 S-6
152-0335-01 152-0335-01 Discrete component 150 ps step recovery diode 1502 S-2 S-4 S-6
155-0001-00 155-0001-00 Hybrid integrated circuit gate assembly S-4