Tektronix S-4 User manual

TEK aaa
070-0896-01
Product Group 42
S-4
SAMPLING HEAD
Please Check for
CHANGE INFORMATION
at the Rear of This Manual
First Printing JAN 1969
—,_ Revised OCT 1986

Copyright © 1969, 1983 Tektronix, Inc. All rights reserved.
Contents of this publication may not be reproduced in any
form without the written permission of Tektronix, Inc.
Products of Tektronix, Inc. and its subsidiaries are covered
by U.S. and foreign patents and/or pending patents.
TEKTRONIX, TEK, SCOPE-MOBILE, and oi are
registered trademarks of Tektronix, Inc. TELEQUIPMENT
is a registered trademark of Tektronix U.K. Limited.
Printed in U.S.A. Specification and price change privileges
are reserved.
INSTRUMENT SERIAL NUMBERS
Each instrument has a serial number on a panel insert, tag,
or stamped on the chassis. The first number or letter
designates the country of manufacture. The last five digits
of the serial number are assigned sequentially and are
unique to each instrument. Those manufactured in the
United States have six unique digits. The country of
manufacture is identified as follows:
BO00000 Tektronix, Inc., Beaverton, Oregon, USA
100000 Tektronix Guernsey, Ltd., Channel Islands
200000 Tektronix United Kingdom, Ltd., London
300000 Sony/Tektronix, Japan
700000 Tektronix Holland, NV, Heerenveen,
The Netherlands

S-4 Sampling Head
CONTENTS
Section 1 Specification
Section 2 Operating Instructions
THE FOLLOWING SERVICING INSTRUCTIONS
ARE FOR USE BY QUALIFIED PERSONNEL ONLY.
TO AVOID PERSONAL INJURY, DO NOT PERFORM
ANY SERVICING OTHER THAN THAT CONTAINED
IN OPERATING INSTRUCTIONS UNLESS YOU ARE
QUALIFIED TO DO SO.
Section 3 Circuit Description
Section 4 Performance Check/Calibration
Section 5 Maintenance
Section 6 Options
Section 7 Electrical Parts List
Section 8 Diagrams
Section 9 Mechanical Parts List Information
Mechanical Parts List Illustrations
Accessories
Abbreviations and symbols used in this manual
are based on or taken directly from IEEE Stan-
dard 260 “Standard Symbols for Units,” MIL-
STD-12B and other standards of the electronics
industry. Change information, if any, is located
at the rear of the manual.

S-4 Sampling Head
mVOLTS/DIV
TYPE S-4
SAMPLING HEAD
fe anton +5v MAX
TEKTRONIX® 4
Fig. 1-1. Type S-4 Sampling Head.
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Section 1—S-4 Sampling Head
TYPE S-4 SPECIFICATION
GENERAL INFORMATION
The type S-4 Sampling head is an input signal processing
unit for Tektronix sampling units. Input characteristics of the
sampling system are determined by the Type S-4. The Type
S-4 has an input impedance of 50 Q and rise time of 25 ps
or less.
The Type S-4 can be installed directly into a sampling
unit or used remotely on optional 3 foot or 6 foot extender
cable. A portion of the signal delivered to the sampling head
input is coupled to the sampling unit for use as an internal
trigger signal. Use of this trigger pickoff signal is dependent
upon the type of vertical sampling unit and sampling sweep
unit used in the system. See the instruction manual for your
vertical sampling unit and sampling sweep unit for further
information.
The vertical deflection factor of the sampling system is
labeled at the top of the Type S-4 as mVOLTS/DIV. The
label refers to the sampling unit Units/Div switch.
NOTE
The electrical characteristics in this section are appli-
cable for an instrument calibrated with ambient tem-
peratures between +20°C and +30°C, and after a 5
minute warm-up. Unless otherwise stated, electrical
characteristics apply over an operating temperature
range from 0°C to +50°C and to an altitude of
15,000 feet. Supplemental information items are for
information only and are not specifications.
Table 1-1
SPECIFICATIONS
Characteristic
Performance Requirements
Supplemental Information
Step Response
Displayed Noise
Risetime 25 ps or less
Observed with
S-50 or S-52 35 ps or less
Aberrations Time From Step
With S-50 or With 284
S-52
0 - 400 ps 400 ps - 25ns After 25 ns
—10%, +10% 0%, +10% or +2%, —2% Ol
or less; total less; total less less; total less
less than 20% than 10% p-p than 4% p-p
p-p
5 mV or less, measured tangentially
1-1

Type S-4 Specification—S-4 Sampling Head
Table 1-1 (cont)
Characteristic
Performance Requirements
Supplemental Information
Dot Transient Response
Within 5% for input signals up to 500 mV P-P
Plug-in unit may require adjustment of
DOT RESPONSE control when switch-
ing Units Div. Avalanche voltage may
have to be readjusted with extreme
ambient temperature.
Signal Voltage
Maximum Operating
1V P-P
Maximum DC limits which may be dis-
played depend on DC OFFSET range
and Deflection Factor
Safe Overload
Do not exceed + or —5 V limits
Input R
50 2 within 5%
Baseline Shift With
Repetition Rate Change
10 mV or less from 30 Hz to 50 kHz
Temperature
Nonoperating —40°C to +65°C
Operating 0°C to +50°C
Altitude
Nonoperating To 50,000 feet
Operating To 15,000 feet
Vibration
Operating 15 minutes along each axis at 0.015”. Vary
the frequency from 10 to 50 to 10 c/s in
1-minute cycles. Three minutes at any
resonant point or at 50 c/s
Shock
Nonoperating 1000 g’s, 1/2 sine, 1/2 ms duration,
2 shocks per axis. Total of 6 shocks
Transportation Qualifies under National Safe Transit
Committee Test Procedure Category IV
(48 inch drop)
—,

Section 2—S-4 Sampling Head
OPERATING
INSTRUCTIONS
General Information
This section provides the basic information required for
operation of the Type S-4 Sampling Head.
The Type S-4 can be used on an extender cable without
compromising the response of the measurement system.
Signals are applied to the 50 Q input of the samping head
through a 3 mm, 50 2 coaxial connector.
Unity loop gain can be obtained with input signals of up
to 0.5 volt (peak-to-peak). Unity loop gain ensures the most
accurate displays during fast changes in input signal ampli-
tude. See the Basic Sampling Principals Section of your
sampling unit manual for further information.
The Type S-4 may be used with input signals up to 1 volt
(peak-to-peak). Specifications for the Type S-4 Sampling
Head are given in Section 1 of this manual.
NOTE
Attenuators, with threaded 3mm connectors, are
available as optional accessories. These attenuators
are useful in reducing the amplitude of large signals.
Other optional accessories with 3mm connectors in-
clude coaxial cables, a 50 2 termination, and adapters
for interconnecting various types of connectors.
Installation instructions are located in the vertical sam-
pling unit instruction manual.
Effect of Excessive Input Voltage
A maximum operating signal voltage of 1 volt (peak-to-
peak) is specified for the Type S-4 in Section 1 of this man-
ual. Signals having an amplitude of more than 1 volt (P-P) at
the Type S-4 input may be distorted by the samping head.
Large signals must be reduced in amplitude to not more
than 1 volt (P-P) at the Type S-4 input.
Signals in excess of plus 5 volts or minus 5 volts may
destroy the sampling diode bridge.
A 15 volt (P-P) signal can be reduced to a suitable ampli-
tude at the Type S-4 input by inserting a series combination
of 10X and 2X attenuators in the coaxial line delivering the
signal. A series combination of 10X and 5X attenuators
would also be satisfactory.
See the discussion on Sine Wave Signal measurements
later in this section for information on signal amplitude affect
upon display amplitude accuracy.
Risetime Measurements
Accurately determining risetime from an observed display
requires that the position of the 10% and 90% points be
accurately known and that the horizontal distance between
these points be accurately measured. The timing accuracy
of the sampling sweep unit must also be known. Switching
the sampling sweep unit from one oscilloscope to another
requires readjustment of the horizontal gain control on the
sampling sweep front panel. See your sampling sweep unit
instruction manual for timing accuracy specifications and
complete instructions for checking timing.
Displayed Risetime and Actual Risetime
Differences in displayed and actual signal risetime will
result unless the risetime of the sampling system is about
four times faster than the risetime of the signal to be mea-
sured. As used in this discussion, the sampling system is
considered to be made up of the sampling head and any
coaxial line, connectors or accessories between the signal
source and the sampling head. Displayed risetime is depen-
dent upon the risetime of the sampling head, the risetime of
the pulse generator, and the risetime of the cable and con-
necting components between the generator and sampling
head. With signals as fast as about 100 ps arriving at the
Type S-4 input, the displayed risetime will be very close to
the actual signal risetime.
Since the risetime of the Type S-52 Pulse Generator out-
put signal is much faster than 100 ps, the displayed risetime
(with this pulse applied to the Type S-4 input) will not be the
actual signal risetime.
The risetime of signals that are faster than 100 ps can
still be determined using the Tektronix Type S-4 Sampling
head. However, the signal risetime is calculated using for-
mula (2-2). Signal risetime calculated using formula (2-2) will
provide a close approximation of the actual signal risetime.
2-1

Operating Instructions—S-4 Sampling Head
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Fig. 2-1. Special S-4/S-52 system risetime measurement
technique.
The relationship between displayed risetime, signal
risetime, signal path risetime, and sampling head risetime is
shown by formula (2-1). T, of signal path, and T, of Type S-4
in formula (2-1). T, of signal path includes the combined
risetime of all coaxial cables, connectors, or accessories be-
tween the signal source and the Type S-4 input. If the signal
path consists of a coaxial cable having a risetime of 8 ps
and connectors and accessories having a risetime of 6 ps,
the combined signal path risetime is
(8)? + (6)? = 10 ps
T, (displayed) ~
V(T, signal)? + (T, of sig. path)? + (T, of Type S-4)? (2-1)
For example, assuming an input signal having a risetime
of 25 ps; connecting cable, accessories, and connectors
having a risetime of 10 ps; and a sampling head with a
risetime of 25 ps gives:
T,
(displayed)
~
V(25)
+ (10
+
(25)
T,
(displayed)
~
y625
+
100
+
625
T,
(displayed)
~
37
ps
Transposing formula 2-1 to permit calculation of signal
risetime when the displayed risetime, signal path risetime,
and sampling head risetime is known gives:
T, (signal) ~
(T, displayed)? + (T, of Type S-4)* — (T, of sig. path)?
(2-2)
Additional information concerning the effect of connect-
ing cables on the displayed signal risetime may be found
under Cable and Accessory Considerations later in this
section.
2-2
Sine Wave Signal measurements
The parameters of the Type S-4 are specified using pulse
or time domain parameters and nomenclature. The fre-
quency response characteristics of the unit, while not speci-
fied, are such that it may be used for relative sine wave
measurements through its calculated upper 3 dB rolloff
point of 14 GHz.
Because of the traveling wave gate used in the Type S-4,
it is capable of handling very large signals as compared to
other microwave samplers. Even so, the peak to peak signal
amplitude should be held to as low level as possible con-
sistent with good signal to noise ratio when making checks
in the 5 to 15 GHz region to avoid compression effects.
Cable and Accessory Considerations
When connecting a signal to the Type S-4 it is important
that the signal coupling cable, connectors, attenuators and
any other devices between the signal source and sampling
head have the correct characteristic impedance, be capable
of handling the signal frequency without causing excessive
loss or distortion, and be of high quality. Care must be taken
to firmly tighten all connectors, or unwanted reflections may
result.
Accurate displays of signals containing very fast transi-
tions or very high frequencies are possible only if the cables
carrying the signal to the sampling head do not distort the
signal. The Type S-4 input resistance is 50 2 and requires
the use of high quality, low loss, 50 2 coaxial cables and
attenuators between the signal source and the sampling
head input cohnector. Using an adapater to change from
3 mm to a larger diameter coaxial cable will result in a loss
of
system bandwidth.
The Type S-4 sampling head is useful from DC up to at
least 14 GHz. Standard and optional 3mm accessories
available from Tektronix are intended for use at frequencies
to 18GHz and are generally useful at frequencies to
25 GHz. Since any accessories in the path between the sig-
nal source and the Type S-4 input will increase the displayed
signal risetime, use only high quality accessories of ade-
quate high frequency capability. Accessories (3 mm) sup-
plied with the Type S-4, or available as optional equipment,
include flexible and rigid coaxial cable, attenuators, adapters
to change from 3mm to larger size coaxial cable, and a
power divider.
The physical and electrical characteristics of the cable
determine the characteristic impedance, velocity of propa-
gation and nature of signal losses.
It is important to use cables or airlines, in the signal-
handling side of the system, that are as short as possible.

Use of the optional 3 foot or 6 foot head extender cable
permits locating the Type S-4 near the signal source and
thereby keeps the input coaxial cable short and signal
losses to a minimum. Signal losses along a coaxial line, due
to skin effect or dielectric loss, result in a loss of high-fre-
quency signal amplitude as the signal travels along the line.
Dielectric loss along the coaxial line also results in an in-
crease in the displayed risetime of fast step pulses. Dielec-
tric and skin effect losses increase with signal frequency
and the length of the coaxial cable. Fig. 2-2A shows the
displayed waveform when the 25 ps output pulse of the
Type S-52 is fed to the Type S-4 input through a rigid 3 mm
coaxial line. In Fig. 2-2B the 25 ps pulse is fed to the S-4
input through a 5 ns length of flexible 3 mm coaxial cable.
Fig. 2-2C shows the risetime of the displayed signal when
the same 25 ps pulse is sent through a 5 ns length of good
quality coaxial cable similar to Type RG-58/U. The impor-
tance of using a short length of the proper type coaxial be-
tween the signal source and the Type S-4 input is apparent
from comparison of the waveforms of Fig. 2-2.
Another factor that can result in loss of signal in a coaxial
cable is use of coaxial cable having a diameter that is large
compared to the wavelength of the highest frequency com-
ponents of the signal. The Type S-4 input connector is in-
tended for use with Teflon dielectric coaxial cable having an
outer conductor with an outside diameter of 0.141 inches.
Resistive losses in large diameter coaxial cable is less
than in smaller diameter cable for frequencies below the crit-
ical value.
The two coaxial lines listed under part numbers 015-
1015-00 and 015-1005-00 must be treated with care
to obtain maximum life and least signal distortion. The
rigid line may not have its shape changed and still
have the propagation delay and Z, guaranteed. In
cases where the line is not used at its maximum per-
formance limits, small amounts of bending can be
made providing mating connectors are on each end
before bending. If bent to a curve radius of 1 1/2
inches, the line may be made totally inoperative. The
flexible cable must not be given a bend radius less
than 10 times its OD, or approximately 2 1/4 inches.
Flexible cables may suffer outer conductor breakage
by tighter bending. Few flexures assure longer life.
Operating Instructions—S-4 Sampling Head
a
eae ror
eee ee
20 ps/div
100 mV/div
20 ps/div
100 mV/div
bi.
aes
Me
LL
(C) 5ns length of cable similar to RG 58/U.
0896-05
Fig. 2-2. Effect of cable length, diameter, and quality on dis-
played risetime.
2-3

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