Tektronix 284 User manual

INSTRUCTION
MIAN UAL serial Number 226 2 BI?
Tektronix,
Inc.
S.W.
Millikan
Way
@
P.
©.
Box
500
@
Beaverton,
Oregon
97005
@
Phone
644-0161
@
Cables:
Tektronix
070-0754-00 1067

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Type 284

TYPE 284 PULSE GENERATOR
SOUSARE WAVE AMPLITUDE PERIOD
BATE:
SOS)
SQUARE
Wave
SINE
WAVE
100 av WOns TOMS ode
Ce elllaldiesd INFO 808”
Satta [ie wrioes OR
QUTPUT
eae
~
SINE
WAVE
OUTPUT
TeS
POpey
EF
BOOMV
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| TERTRONIX, INC,
PORTLAND, OREGON, U.S. A
TEKTRONIX
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Fig. 1-1. Type 284 Pulse Generator.
Type
284
@i

Type 284
SECTION |!
SPECIFICATION
Change information, if any, affecting this section will be found at the
rear of the manual.
Introduction
The Tektronix Type 284 Pulse Generator provides special-
ized signals that are defined sufficiently fo allow them to be
used to verify the performance of fast general purpose and
sampling oscilloscopes. Specifically, the signals allow a check
of the vertical amplifier risetime, deflection factor accuracy,
transient response and pulse flatness deviation (aberrations);
plus checking upon the accuracy of horizontal sweep rates.
The fast pulse may be used as a signal source for testing the
risetime of transistors and amplifiers, or for Time Domain Re-
flectometry.
Each signal provides a trigger signal for externally trig-
gering an oscilloscope time base generator. The fast pulser
also generates a trigger in advance of the fast step, provid-
ing the pretrigger signal necessary for some sampling oscil-
loscopes.
Regulated DC power supplies assure stable operation over
a wide range of line voltage and frequency. Circuits are
temperature compensated to maintain both amplitude and
frequency accuracies over a wide temperature range.
The electrical characteristics that follow are divided
into two categories. Information listed in the Performance
Requirement column applies directly to the instrument per-
formance and is a commitment by Tektronix, Inc., to the
customer. Information listed in the Operational Information
column is for clarification and operator convenience and is
not to be used to specify any performance limits for the in-
strument. Characteristics listed in the Performance Require-
ment column are checked by the Performance Check pro-
cedure, Section 5, of this manual. Any instrument not meeting
these performance limits can be brought within specifications
by performing the Calibration Procedure, Section 6 of this
manual. The performance requirements apply over an
ambient temperature range of 0° C to +50°C, at altitudes
up to 5,000 feet, with upper temperature limit decreased
by 1° C per 1000 feet from 5000 feet to 15,000 feet, after
a warm up period of five minutes, providing the convection
cooling holes (bottom and both sides) are not obstructed. The
unit may be stored in temperatures from —40° C to +65° C.
ELECTRICAL CHARACTERISTICS
Characteristic |
Operational Information
Performance Requirement |
SINE WAVE OR SQUARE WAVE OUTPUT
Calibrated PERIOD Signals
Square Wave 10 ws, 1 ws and 100 ns
For checking sweep rates.
Sine Wave 10 ns and J ns
Signal Amplitude Into 500
Square Wave 1V, 100 mV and 10 mV
For checking deflection factors.
Sine Wave 100 mV For checking horizontal timing only.
Accuracies SIGNAL SIGNAL
Square Wave Sine Wave Square Wave
PERIOD 10 ss 1 us 100 ns 10ns | Ins 10us | lps | 100ns
Timing +0.5% +0.5% +0.05% | 1% | 1% | Amplitude accuracies in this col-
Amplitude 1V +0.5% | +05% | 42% umn are based upon DC testing
of attenuators.
100 mV +20% | 20% | +1% +1% +2.5%)
10 mV +1.5% +15% +3%7
Square Wave Duty Factor
48% to 52%
Trigger Output Signa!
Amplitude, into 500
Square Wave
+200 mV, 20%
Sine Wave 200 mV peak to peak, +40%
1Measured 20ns after pulse reaches 100% on Tektronix Type 383 or 453 Sampling Probe Unit.
100% on Tektronix Type 451 Dual Trace Sampling Unit.
®
Measured 30 ns after pulse reaches
1-1

Specifications—Type 284
ELECTRICAL CHARACTERISTICS (cont)
PULSE GENERATOR
Characteristic
Performance Requirement
Operational Information
Repetition Rate 50 kHz, +10% 20 ws period
Risetime, 10% to 90% | <70 ps
Amplitude
into
500
>
+200
mV
Step
beginning
adjusted
to
zero
volts
during calibration.
Pulse Flatness Deviation
During first 2s after pulse reaches 100%
amplitude: <3% p-p total deviation over
a range from +3% to —3%. After 2ns:
<2% p-p total deviation over a range
from +2% to —2%.
Aberrations
Internal Pulser Assembly Signal
Reflections due to changes of im-
pedance
<+5%, measured by Tektronix Type 182
TDR unit.
L BS, +50%, —0%
Pulse Duration, 50% to 50%
TRIGGER OUTPUT SIGNAL WHEN USING PULSE GENERATOR
Amplitude +200 mV, +20%
Risetime, 10% to 90% <3 ns
Pulse Duration, 50% to 50% >10 ns
Trigger Pulse Occurrence In Ad-
vance of PULSE OUTPUT Signal
5 ns or 75 ns, 5 ns?
Selectable by LEAD TIME switch
POWER LINE REQUIREMENTS
Line Voltage Ranges
115 Volt Line
90 VAC to 136 VAC
230 Volt Line
180 VAC to 272 VAC
Frequency Range
48 Hz to 440 Hz
Maximum Power Consumption
Approximately 6.5 Watts at 115 VAC 60 Hz
Fuse Data
Use Fuses listed in Parts List
MECHANICAL CHARACTERISTICS
Dimensions
Height 63/, inches
Width 41/, inches
Length 15 inches
Approximate dimensions include knobs and connectors.
Construction—Aluminum alloy chassis with epoxy laminated
circuit boards. Front panel is anodized aluminum.
Accessories—An illustrated list of the accessories supplied
with the Type 284 is at the end of the Mechanical Parts
List pullout pages.
Serial numbers BO10100-B020235; 5 ns or 50ns, +5 ns.
1

Type 284
SECTION 2
OPERATING INSTRUCTIONS
Change information, if any, affecting this section will be found at the
rear of the manual.
General
This section of the manual provides the basic information
required for operation of the Type 284. Instructions include
function of the front panel controls and connectors, first time
operation, general operating infromation, and basic appli-
cations.
AC Power Considerations
The Type 284 can be operated from either a 115 or a
230-volt line, at frequencies from 48 to 440Hz. The AC
line voltage selector panel and fuse holder is located on
the rear panel of the Type 284.
CAUTION
The Type 284 should not be operated with the volt-
age selector in an incorrect position for the nominal
line voltage applied. Operation of the instrument
in a wrong voltage range will either provide incor-
rect operation or damage the instrument.
The AC line voltage selector panel on the rear of the Type
284 indicates nominal line voltage selected. See Fig. 2-2.
Check to see that the plastic indicating tab of the line se-
lector is protruding through the selector panel, indicating
that its position is proper for applied nominal line voltage
(115 or 230 AC Volts).
The selector assembly cover can be removed to change the
nominal line from 115 Volts to 230 Volts or vice versa, or
to replace the fuses. Use the following procedure:
1. Disconnect the instrument from the power source.
2. Loosen the two captive screws which hold the cover
onto the voltage selector assembly, then pull to remove the
cover.
3. To convert from 115-volt to 230-volt nominal line volt-
age or vice versa, pull out the Voltage line selector switch
bar; turn it 180° and plug it back into the remaining holes.
Change the line cord to fit the power source receptacle or use
a line cord adapter.
4, It is not necessary to change fuses if the range is
changed; however, in the 230 volt range both fuses are in
use. Also in checking the fuses, the upper fuse (1/10 A) for
the 115 volt range has a nominal resistance of approximate-
ly 80 ohms, and the lower fuse (1/16 A) for the 230 volt range
has a nominal resistance of approximately 150 ohms.
5. Re-install the selector assembly cover and tighten the
two captive screws.
6. Before applying power to the instrument, check that
the indicating tab of the line selector is protruding through
@
the selector panel indicating that its position is proper for
the applied nominal line voltage range (115 or 230). In
the 115 volt nominal range, the regulating range is from 90
to 136 volts. In the 230 volt nominal range the regulating
range is from 180 to 272 volts.
Handle and Stand
The bail-type handle of the Type 284 can be pulled out
for convenient carrying of the instrument. When not in use,
the handle folds out of the way into the trim of the instru-
ment cabinet. See Fig. 2-1.
The bail-type stands are mounted beneath the cabinet.
The stands permit the Type 284 to be tilted for convenient
operation as shown in Fig. 2-1. The instrument may also
be set on the rear feet either for operation or storage.
Fig. 2-1. Type 284 showing handle and stand.
CONTROLS AND CONNECTORS
A brief description of the function and operation of the
front and rear panel controls and connectors follows. Fig.
2-2 shows the front and rear panels of the instrument. More
detailed operation is given in this section under General
Operating Information.
2-1

Operating Instructions—Type 284
(A) Front Panel
TYPE 284 PULSE GENERATOR
SQUARE WAVE AMPLITUDE PERIOD
ARTO Sa SQUARE WAVE SINE WAVE
WOO nv 2ANNMV
WDOns 100s
— NTO SON
ns
> SQUARE WAVE.
_ PULSE i
SINE“ WAVE -OUTPUT
font 500: oo:
OUTPUT
TB Wipe = +AODAN
(B}) Rear Panel
bes FREQ: 48-TO 440Hz
LING FUSE > -
- (LRea SOW }
80 re 138
{BU-to 272 30
_ PABA SLOW
AMP: (MAK) 0:05
“oe AAT. TBV-60H2)
Nominal 115 AC Line V position
Nominal 230 AC Line V position
Fig. 2-2. Front and rear-panel controls and connectors.
@2

Front Panel
SQUARE WAVE
AMPLITUDE
PERIOD
MODE
PULSE OUTPUT
TD BIAS
LEAD TIME
TRIGGER
OUTPUT
SQUARE WAVE
OR SINE WAVE
OUTPUT
POWER
Rear Panel
Line voltage
selector
Power
Connector
Selects three amplitudes of square wave
output signal voltages: 10mV, 100 mV,
and 1 V (into a 50Q load).
Selects the time periods of the SQUARE
WAVE OR SINE WAVE outputs. The
SQUARE WAVE output time periods are
10 ys, 1 ys and 100ns with amplitude
selected by the SQUARE WAVE AMPLI-
TUDE switch. The SINE WAVE time peri-
ods are 10ns and Ins with approximate
amplitudes of 100 mV (into a 50 Q load).
Selects either the PULSE OUTPUT or the
SQUARE WAVE OR SINE WAVE OUT-
PUT to their respective connectors.
Output connector for the PULSE OUTPUT
(rise time < 70 ps, amplitude > 200 mV).
Adjusts the bias of the tunnel diode af-
fecting the PULSE OUTPUT.
Selects either 5ns or 75ns of LEAD TIME
of the TRIGGER OUTPUT signal with ref-
erence to the PULSE OUTPUT signal.
Output connector for the trigger signal
pickoff, a portion of the signal from either
the PULSE OUTPUT or the SQUARE WAVE
OR SINE WAVE OUTPUT depending upon
the position of the MODE switch.
Output connector for the SQUARE WAVE
OR SINE WAVE OUTPUT as selected by
the SQUARE WAVE AMPLITUDE and PERI-
OD switches.
Light: Indicates when POWER switch is
ON and the instrument is connected to a
power source.
Switch: Applies power to the instrument.
Switching assembly to select the nominal
operating voltage (115V or 230V). This
assembly also includes the line fuses.
Input connector for line power.
FIRST-TIME OPERATION
The following steps will demonstrate the use of the con-
trols and connectors of the Type 284. It is recommended
that this procedure be followed for familiarization with this
instrument. In this procedure a Tektronix Type 561A Oscil-
loscope is used with a Type 3S] Dual-Trace Sampling Unit
and a Type 3T2 Sampling Sweep Unit. If other equipment
is used the control settings and the procedure will be dif-
ferent. If you are not familiar with the operation of the
oscilloscope with its sampling plug-in units, read the First
Time Operation portions of the manuals for these instruments
before proceeding.
@1
Operating Instructions—Type 284
Setup information
1. Set controls as follows:
Type 284
SQUARE WAVE
AMPLITUDE
PERIOD
MODE
LEAD TIME
Type 3581
Display Mode switch
Smooth-Normal switch
A Position
B Position
DC Offset +1 V,
Channel A
DC Offset -E1 V,
Channel B
mVolts/Div, Channel A
mVolts/Div, Channel B
Variable mVolts/Div
(both channels)
Invert-Norm switch,
Channel A
Invert-Norm switch,
Channel B
Internal Trigger
Sampling Mode
Type 372
Time Position
Time Position Fine
Horiz Position
Samples/Div
Range
Start Point
Display Mag
Time Magnifier
Time Magnifier Variable
Display Mode
Trigger Sensitivity
Recovery Time
Polarity
Source
Samples/Div (an Internal
Switch)
1.0 V
10 ps
SQUARE WAVE OR SINE
WAVE OUTPUT
(to right)
5ns
Chan A
Normal
Midrange
Midrange
Midrange (5 turns from
one end)
Midrange (5 turns from
one end)
200
200
Cal
Norm
Norm
Off
Triggered
Fully Clockwise
Fully Clockwise
Midrange
Midrange
10 us
With Trigger
X1
x1
Cal
Normal
Fully Clockwise
Midrange
Ext
100 (up position)
2. Connect the Type 284 to a power source that meets
the voltage and frequency requirements of the instrument.
Check to see that the plastic indicating tab on the line se-
lector panel on the rear of the instrument is protruding
through the selector panel indicating that its position is
2-3

Operating Instructions—Type 284
proper for the applied nominal line voltage (115 V or 230 V).
See AC Power Considerations in this section for instructions
to change the nominal line voltage if necessary.
3. Set the Power switch to ON on the Type 284 and also
on the Test Oscilloscope, and allow five minutes warm up
before proceeding.
Square wave output
4. Connect the Type 284 SQUARE WAVE OUTPUT signal
through a 50 coaxial cable with GR type connectors to
the A input Connector on the Type 3S1. Connect the TRIG-
GER OUTPUT signal through a 509 BNC type coaxial
cable
to the 50Q Trigger Input connector on the Type 3712.
5. Turn the Trigger Sensitivity fully counterclockwise, then
slowly clockwise until a stable display is obtained. See
Fig. 2-3A. Normal slight changes of the Samples/Div con-
trol on the Type 312, the A Position control on the Type
3S1 may be necessary to display this waveform.
Fig. 2-3. Typical SQUARE WAVE OUTPUT display (1 Volt into
502 load) for two time periods.
2-4
6. Change the Type 284 PERIOD switch to 1 us and change
the Type 3T2 Range switch to 1 us (Time/Div 100 ns). Ob-
serve a similar display to that in preceeding step.
7. Change the Type 284 PERIOD switch to 100ns and
change the Type 312 Range switch to 100ns (Time/Div 10
ns). Observe a display similar to Fig. 2-3B.
8. Change the Type 284 SQUARE WAVE AMPLITUDE
switch to 100mV and change the Type 3S1 Channel A
mVolts/Div switch to 50. Observe a 2 division display sim-
ilar to the 5 division display in Fig. 2-3B.
9. Change the Type 284 SQUARE WAVE AMPLITUDE
switch to 10 mV and change the Type 3S1 Channel A mVolts/
Div switch to 5. Observe 2 divisions of display with the nor-
mal noise of the Type 381 showing up at this sensitivity.
Sine Wave Output
10. Move the trigger signal coaxial cable on the Type
312 from the 50Q input connector to the 1 MQ/UHF Sync
connector. Set the Type 284 PERIOD switch to 10 ns SINE
WAVE and set the Channel A mVolts/Div switch on the
Type 3S1 to 50. Slight change in the Trig. Sensitivity control
on the Type 312, and in the A Position contro] on the Type
3S] may be necessary to obtain a display similar to Fig.
2-4A.
11. Set the PERIOD switch to 1 ns SINE WAVE on the Type
284 and set the Time Magnifier switch on the Type 312
to X10 (Time/Div 1 ns). Observe the 1 ns period sine wave
similar to Fig. 2-4B. Slight change in the Trig. Sensitivity
control, and the Recovery Time control on the Type 312
may be necessary to obtain a stable display.
Pulse Output
12. Move the signal coaxial cable on the Type 284 to
the PULSE OUTPUT connector, and set the MODE switch to
the PULSE OUTPUT position (to the left). Set the Time Mag-
nifier switch on the Type 312 to X1 (Time/Div 10 ns), and
turn the Trig. Sensitivity switch fully counterclockwise then
clockwise for a stable trace. Change the LEAD TIME switch
to 75ns position and note the change in delay time of ap-
proximately 70 ns as shown in Fig. 2-5B.
NOTE
Since the tunnel diode pulse generator is an inte-
gral part of the PULSE OUTPUT connector, mechan-
ical strain on the PULSE OUTPUT connector will
cause slight mechanical changes in the tunnel di-
ode assembly. Slight adjustment of the TD BIAS
control, a screwdriver adjustment on the front
panel, will correct the display. For the TD BIAS
adjustment procedure see the General Operating
Instructions.
CONTROL SETUP CHART
Fig. 2-6 is a control setup chart for the front and rear
panels of the Type 284. This figure may be reproduced
and used as a test setup record for special applications or
procedures. It may also serve as a training aid to facilitate
control operation.

Fig. 2-4. Typical SINE WAVE OUTPUT display showing (A) 10 ns
and (B) 1ns time period.
GENERAL OPERATING INFORMATION
Mode Switch
The MODE switch selects one output with its trigger signal.
The MODE switch always turns the power off on one output
which prevents both trigger signals from appearing at the
TRIGGER OUTPUT at the same time.
Square Wave Output
Tne SQUARE WAVE OUTPUT amplitude is selected by
the SQUARE WAVE AMPLITUDE switch, and the time period
is selected by the PERIOD switch on three of its positions.
Note that the other two positions of the PERIOD switch
select the SINE WAVE time period. In order to maintain the
output selected by the SQUARE WAVE AMPLITUDE switch,
an output load of 509 is required. For further loads use
the following formula to calculate the output voltage:
Rioad
ut
Rioad
+
50
x
(
Operating Instructions—Type 284
Pare
a a
Fig. 2-5. Typical PULSE OUTPUT display, showing a double ex-
posure of two positions of LEAD TIME switch.
(E is the Voltage selected by the SQUARE WAVE AMPLI-
TUDE switch)
Fig. 2-7 shows the time period and amplitude measurement
points. In this display the output of the Type 284 is properly
terminated by being coupled to the 50Q input of a sam-
pling oscilloscope. Disregard the overshoot at the top
corner of the square wave in making amplitude measure-
ments. The time period measurement (here a period of
100 ns) is the time of one cycle of the square wave.
The square wave output desired can be selected for am-
plitude from 1V, 100mV or 10 mV and for the time period
from 10 ps, 1 us or 100 ns.
Sine Wave Output
The SINE WAVE OUTPUT is selected by the PERIOD
switch. The period switch selects either a 10ns or a Ins
sine wave time period. The time period is the time of one
cycle of the sine wave. The amplitude is approximately
100 mV when it is connected into a 50Q load.
2-5

Operating Instructions—Type 284
(— )
TYPE 284 PULSE GENERATOR
SQUARE WAVE AMPLITUDE PERIOD
UNTO S081 SQUARE WAVE SINE WAVE
100mV 100ns 10ns = 100m
INTO son
10mV
Py
10us
MoprE SQUARE WAVE
PULSE cr sarees ans OR
OUTPUT ae SINE WAVE OUTPUT
7, S 70ps, = +200mV
Bias
(cc
=)
2)
©
(“=r
050
TRIGGER
OUTPUT
LEAD TIME
Sas (_L js.
SERIAL = 500 TEKTRONIX, INC.
SY PORTLAND, OREGON, U.S. A.
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(A) FRONT PANEL
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@
LINE FUSE
[ex stow |p
230V FUSE
[izza stow |p
FREQ 45 TO 440Hz
90 To 136
()
\} 180 10 272 230 G
NS Ya
WATTS (Max) 6.5
AMP = (MAX) 0.05
(AT T15V-60Hz)
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386-128 ())
(B) REAR PANEL
2-6
Fig. 2-6. Control setup chart.
@2

Mm 200 mV/Div
Fig. 2-7. Typical display showing amplitude and period measure-
ments. A 1 Volt amplitude, 100 ns time period pulse from the
Type 284 into 502 input of Sampling oscilloscope.
Pulse Output
The Pulse Output power is turned on by setting the Mode
switch to its left position. The pulse is generated by a tun-
nel diode in a coaxial environment and connected directly
to the PULSE OUTPUT connector. A screwdriver adjustment
marked TD BIAS (tunnel diode bias) on the front panel is
used to adjust the optimum voltage of the tunnel diode.
Mechanical strain on the front panel connector may change
the tunnel diode environment and a slight adjustment of the
TD BIAS may be necessary. To obtain the power adjustment
of the TD BIAS, it is necessary to observe the display on a
sampling oscilloscope. Following is a setup procedure us-
ing a Tektronix Type 561A with a Type 381 Dual-Trace
Sampling Unit and a Type 3T2 Sampling Sweep Unit. If
other equipment is used, the control settings and the pro-
cedure will be different.
NOTE
An internal TD Bias adjustment (R133) is provided
for coarse adjustment of tunnel diode bias. If the
tunnel diode is replaced or if the front panel con-
trol doesn't provide a satisfactory setting adjust the
TD Bias (internal) in the manner given in the Cali-
bration section of this manual.
1. Set the controls as follows:
Type 284
MODE switch Pulse Output (to (left)
LEAD TIME 5 ns
POWER ON
Type 351
Display Mode switch Chan A
Smooth-Normal switch Normal
A Position Midrange
DC Offset +1 V, Midrange (5 turns from
Channel A one end)
Operating Instructions—Type 284
mVolts/Div, Channel A 50
Variable mVolts/Div Cal
(Channel A)
Invert-Norm switch, Norm
Channel A
Sampling Mode switch Triggered
Type 312
Time Position
Time Position Fine
fully clockwise
fully clockwise
Horiz Position Midrange
Samples/Div Midrange
Range 100 ns
Start Point with Trigger
Display Mag Xx
Time Magnifier x1
Time Magnifier Variable Cal
Display Mode Normal
Trigger Sensitivity Fully clockwise
Polarity +
Source Ext
Samples/Div (an internal 100 (up position)
switch}
2. Connect the Type 284 PULSE OUTPUT signal through a
50 coaxial cable with GR type connectors to the A input
connector on the Type 3S1. Connect the TRIGGER OUTPUT
signal through a 500 BNC type coaxial cable to the 50
Trigger Input connector on the Type 372.
3. If the TD BIAS is at optimum adjustment you will ob-
serve an untriggered display of about 4 divisions or about
200 mV peak to peak as in Fig. 2-8A, and upon turning the
Trigger Sensitivity control almost fully counterclockwise,
observe a clean triggered step display similar to Fig. 2-8B.
Normal slight changes to the’ Type 3T2 Samples/Div control
and the Type 3S1 A Position control may be necessary to
display this waveform.
4. If upon turning the Trigger Sensitivity control almost
fully counterclockwise a trace display appears showing the
position of the upper portion of the pulse, this indicates that
the TD BIAS control is clockwise from the optimum adjust-
ment. See Fig. 2-8C (upper trace). Slight counterclockwise
rotation of the TD BIAS control will be necessary to obtain
a display similar to Fig. 2-8B.
5. Fig. 2-8C (lower trace) display indicates that the TD
BIAS control is counterclockwise from the optimum adjust-
ment. If the display as in Fig. 2-8B cannot be attained with
clockwise rotation of TD BIAS control, refer to the calibration
section of this manual.
The PULSE OUTPUT of the Type 284 has an amplitude of
approximately +200 mV into a 50 load. The pulse width
is approximately 1 ys out of a pulse period of about 20 us.
The rise time of the pulse is equal to or less than 70 ps. With
these specifications, several precautions should be considered
when connecting the Type 284 PULSE OUTPUT signal to a
test device or to a display oscilloscope.
Cable Considerations
The cables that conduct the output to the device under
test should be low-loss 509 coaxial cables to assure that
all information contained in the pulse will be delivered to
the test point without distortion. The physical and electrical
2-7

Operating Instructions—Type 284
Fig. 2-8. Typical display showing adjustment of TD BIAS control.
characteristics of the cable determine the characteristic im-
pedance, velocity of propagation and nature of signal loss.
Since the signal losses caused by energy dissipation in the
dielectric are proportional to the signal frequency, any very
high frequency information in a fast-rise pulse will be lost
in a very few feet of cable. Therefore it is important to use
cables or airlines that are as short as possible.
2-8
Impedance Matching
To provide a smooth transition between devices of differ-
ent characteristic impedance, each device must encounter a
total impedance that is equal to its own characteristic im-
pedance. Thus, when the OUTPUT PULSE signal of the Type
284 is applied to a load other than 509, a suitable im-
pedance matching device must be provided. If the imped-
ances are not matched, reflections and standing waves in the
cables will result in distortion of the signal at the load. In
many cases the load required will be 509, then with the
use of available attenuators, 2X, 5X and 10X (10X
Attenuator, Tektronix Part No. 017-0078-00) will attenuate
the signal and provide the impedance match.
Fig. 2-9 illustrates a simple resistive impedance-matching
network that provides minimum attenuation. To match im-
pedances with the network, the following conditions must
exist:
(Ri + Za) Re must equal Z,; and R, + ZiRe
must
(Ri + Zs) + Re Zi + Re
equal Zo».
Therefore:
RiRo = Z,Z. and RyZ; = Re (Z2 — Z;,)
or Ry = Zp (Zp — Zy);
and R, = Z, 3
As an example, to match a 50-ohm system to a 125-ohm
system:
Z, = 50 ohms; and Z, = 125 ohms.
Therefore:
R, = 125 (125 — 50) = 96.8 ohms
_ 125 _
Ro — 50 125 — 50. = 64.6 ohms
Z, E, R, E. Z5
—> e— ° w—9) <~—.
_ Ro =
~ Z, <Z
To match impedances:
or: R, =y Zo (Z, — Z,) and R, = Z, 2,
2 Vz, —2,
Fig. 2-9. Simple resistive impedance-matching network providing
minimum attenuation.
(1

Though the network in Fig. 2-9 provides minimum attenu-
ation for a purely resistive impedance-matching device, the
attenuation as seen from one end does not equal that seen
from the other end. A signal applied from the lower im-
pedance source (Z,) encounters a voltage attenuation {(A;)
that may be determined as follows:
EF, — E Ep
Since: Ip, = Iza; ———— =
‘ Ry Zo
Therefore: A, = Es = Ry
E.
1; (1 << Ar < 2)
A signal applied from the higher impedance source (Z.)
will encounter a greater voltage attenuation (Az) that may
be determined similarly:
E. _ Ey __ E, 4 E,
Since Ir1 = Ire + !21; R, =~ RR, Z,
Therefore:
_ & | R Ry . 22,
Ag — E, — Ro + 1; (1 < Az < Z, )
In the example of matching 50 ohms to 125 ohms,
96.8
Ai = 125 + ] = 1.77;
968 96.8 _
and A, = oA6 + 50 +1= 444
Note that if the 50-ohm source were used for pulsing a
high-impedance load, R; would approximately equal the
impedance of the load (high R} and R, would approximately
equal the 50 ohms of the pulse source. In this situation,
voltage attenuation would be about 2.
If a low-impedance load (<Q 50 ohms} were to be en-
countered, the 50-ohm pulse source would be the Z, source.
If the load impedance were to approach 0 ohms, the value
of R, would then approach the load impedance (low R).
Voltage attenuation in this case would become quite signif-
icant;
2Z, =
Z.
The illustrated network can “he modified to provide dif-
ferent attenuation ratios by adding another resistor (<Q Rj)
in series between Z, and the junction of Ry and Ro.
Attenuation = (very high)
Risetime Considerations
If the PULSE OUTPUT signal from the Type 284 is to be
used for determining the risetime of a test device or a dis-
play oscilloscope, the risetime of the Type 284 may have to
be taken into consideration. Generally the risetime of the
applied pulse (Type 284 PULSE OUTPUT) should be four
times or more faster than the risetime to be measured. If the
risetime of the applied pulse approaches the risetime of the
system under test the actual risetime may be approximated
from the following equation:
T, measured ~ (T, pulse}? + T, (system)? (2)
Calculations are not necessary if the oscilloscope system or
device system under test or a combination of the device
system
under test and the oscilloscope system has a rise-
time of more than four times the applied pulse (70 ps—Type
284) or 280 ps. The above system includes a short coaxial
Operating Instructions—Type 284
connecting cable and matching attenuators. For long coaxial
cables, a display measurement is recommended because of
the losses introduced by different types of cables.
Trigger Output
The TRIGGER OUTPUT signal is selected with the MODE
switch at the same time and synchronized with either the
PULSE OUTPUT or the SQUARE WAVE OR SINE WAVE
OUTPUT. The amplitude of the TRIGGER OUTPUT signal is
about 200 mV into a 50Q load in all positions. With the
SQUARE WAVE OUTPUT, the 200 mV square wave trigger
signal facilitates easy triggering, especially for the 10 mV
SQUARE WAVE AMPLITUDE. The TRIGGER OUTPUT signal
is a 1 or 10ns sine wave, when the PERIOD and the MODE
switch are selected for 1 or 10ns SINE WAVE OUTPUT.
With the MODE switch in the PULSE OUTPUT position, the
TRIGGER OUTPUT signal leads the PULSE OUTPUT signal
by 5ns or 75ns as selected by the LEAD TIME switch. See
Fig. 2-10.
|) ft | |
TRIGGER OUTPUT
PULSE
OUTPUT|
OUTPUT
LEAD
TIME
10 ns/Div
|i) )i [| ==
TRIGGER OUTPUT
B) SN BO30236 - up.
Fig. 2-10. Typical display showing TRIGGER OUTPUT signal, with
PULSE OUTPUT signal in two positions of the LEAD TIME switch.
2-9

Operating Instructions—Type 284
End Line |
Termination |
Fig. 2-11. Setup for Amplitude checks for (A) 502 system, (B)
Sampling Probe and (C)} Typical waveform.
2-10
BASIC APPLICATIONS
General
The Type 284 is a source of Square Wave, Sine Wave
and Pulse output signals useful to verify the deflection factor
and timing accuracies of Sampling Oscilloscopes. It is also
useful as a signal source for other applications. This part of
the operating instructions will show basic uses of the Type
284.
Checking Amplitude
The Type 284 SQUARE WAVE OUTPUT signal amplitudes
are 1 V, 100 mV, and 10 mV into 50 Q with a selection of the
time PERIOD of 10 ys, 1 us, and 100 ns.
Fig. 2-11A shows Type 284 connected to the Channel A
input of the Type 381 Dual Trace Sampling Unit, used in
the Type 561A Oscilloscope with the Type 3T2 Sampling
Sweep Unit. The vertical deflection factor of other 5092
input oscilloscope can be checked with this simple connection.
Since the Type 284 uses the input of the Sampling unit as a
load, the accuracy of the voltage presented to the input
depends upon the accuracy of the input resistance. The DC
input resistance can be measured with an accurate bridge
with the oscilloscope power off. If external attenuators are
used, their accuracies must be taken into account. Exter-
nally triggering the sampling oscilloscope from the Type 284
permits higher trigger amplitude (200 mV) with 100 mV and
10 mV square wave output.
Fig. 2-11B shows a method of connecting into sampling
oscillosopes with a high impedance input or sampling probe.
The Type VP-2 voltage pickoff adapter permits use of the
high impedance sampling probe to look at signals within a
closed 50 system, with a minimum effect upon the signal.
Then by using an accurate end line termination with the VP-2,
accurate amplitudes are conveyed to the Sampling Probe.
Other high impedance input oscilloscopes can be checked
with the Type 284 if an accurate 50Q termination is pro-
vided and the proper adapter is connected to the oscillo-
scope input.
Fig. 2-11C shows a typical display of a 1 Volt Square
Wave Output 100ns signal used in checking the vertical
deflection of the sampling units.
Checking Equivalent Time Bases
Signals available from the Type 284 for checking time
bases include square waves with time periods of 10 us, 1 ps,
and 100 ns, and sine waves with time periods of 10 ns and
Ins. The amplitude of the signal is not important in check-
ing equivalent time bases-as long as the signal is adequate
to obtain a stable display; however, with the SQUARE WAVE
output, amplitude as well as time verification can be made.
An example of fast verification of the amplitude and time
checks is shown with the Type 182 Sampling Plug-In Fig.
2-12B. A display is shown of the Type 284 SQUARE WAVE
OUTPUT of 1 volt amplitude at a time period of 100 ns. The
SQUARE WAVE signal is connected through a 502 coaxial
cable
to one of the Thru Signal Channel 50 connectors on
the Type 182. The other Thru Channel 509 connector is
terminated with the End Line termination (Tektronix Part No.
017-0083-00). The Trigger Output signal from the Type 284
is connected through a BNC coaxial cable and a BNC to GR
adapter to the Ext. Trig Input connector on the Type 152.
See Fig. 2-12A.
Fig. 2-12C is a display of the 10ns PERIOD SINE WAVE
on the Type 182. The Type 182 is set for 10 ns/Div (Horizon-
tal Units) with .05 Volts/Div (Vertical Unit).
(B)1

502 SOQ
Ceaxial Cable = BNC Coaxial Cable
: i
Sar ieee
4
}
:
t
oe
| |
110 ns/DIV.
| a
(C) Display of 10 ns SINE WAVE.
Fig. 2-12. Setup for display showing timing and Amplitude meas-
urements for Type 152.
Checking Risetime |
The Pulse output from the Type 284 has a risetime of <70
ps, a width of about 1 us, and a repetition rate of about
50 kHz. Risetime verification of Vertical Sampling units with
risetimes equal to or longer than four times the Type 284
applied pulse can be made without calculations. At four
times greater risetime, the error (by using equation 2 in this
®1
Operating Instructions—Type 284
on
|
|
’ Fig, 2-13. Typical displays showing risetime checks.
section) is +3% of the displayed signal. Four times 70 ps
(Type 284 risetime) or about 280 ps, or slower risetime ver-
ticals units can be verified directly.
Fig. 2-13A shows a typical display with the Type 284 Pulse
Output signal connected through a 5ns coaxial cable to one
input connector of the Type 3S1. A Type 561A Oscilloscope
with a Type 31T77A Sampling Sweep Unit was used with the
2-11

Operating Instructions—Type 284
Type 3S1. The risetime is verified from 10% to 90% of the
full amplitude to be equal to or less than 350 ps. Fig. 2-13B
shows a display of the Pulse Output signal fed through a 60
ns 509 coaxial cable. Here the measurement of the display
risetime is taken from the 10% to 90% points of a lower
amplitude. The Pulse does not reach full amplitude in this
display of 100 ps/div.
By changing the equivalent time to 5times slower or .5
ns/div, note the long, gradual slope (Fig. 2-13C) after the
initial rise in the waveform. This distortion is referred to as
“dribble up” characteristic of the coaxial cable. The risetime
is measured from the 10% to the 90% points of the initial
ramp portion of the displayed signal not including the dribble
up portion. The risetime, dribble up and other character-
istics of coaxial cables can be evaluated with a known rise-
time generator and sampling oscilloscope system.
Risetime verification of a system including the display
oscilloscope whose risetime approaches the risetime of the
Type 284 applied pulse, can be approximated by equation
(2) in this section.
Checking Fast Oscilloscope Vertical
Response to a Fast Step Pulse
A fast step pulse will show up various responses in ampli-
fiers due to terminations, mechanical layout, and characteris-
tics of input circuits. The following displays (Fig. 2-14 through
2-21) were taken showing the characteristics of some ver-
tical amplifiers when subjected to the Type 284 Pulse.
The Pulse Output signal of the Type 284 is connected through
a 20Cm, 500 Airline (Tektronix Part No. 017-0084-00} to
the 50Q input sampling oscilloscopes. External triggering
was used with the trigger signal from the Type 284 Trigger
output connector through a BNC coaxial cable to the Ex-
ternal Input of the sampling sweep unit. With the sampling
probe type of sampling oscilloscopes, the output of the Type
284 is connected to a Type VP-2, and an End Line Termination
(Tektronix Type 017-0081-00). The Sampling Probe was in-
serted in the Type VP-2.
Other high impedance oscilloscopes required an accurate
50 Q termination and an adapter to connect to the input.
Fig. 2-14. Typical Type 284 PULSE OUTPUT signal display using Type 451 Vertical Sampling Unit.
tp pe
Fig. 2-15. Typical Type 284 PULSE OUTPUT signal display using Type 4$2A Vertical Sampling Unit.
2-12
©!

Operating Instructions—Type 284
Fig. 2-18. Typical Type 284 PULSE OUTPUT signal display using Type 353 Vertical Sampling Unit.
® 2-13