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Poktronix. Inc.
P-0. BOX 500
Beaverton, Oregon 97005 Serial Number
@/973
070.1598-00
PG 502
Ii,
"B:I@ TABLE
I OF CONTENTS
SECTION 1 OPERATING INSTRUCTIONS Page
Introduction l-l
Instrument Description 1-l
installation and Removal l-1
Operating Considerations 1.2
Output Terminations and Connections 1.2
Maintaining Pulse Fidelity I-2
Impedance Matching I-2
RisetimE Measurements In Linear Systems 1.4
Variable Pulse Delay 1.4
Operating Mode?. 1.5
Period and Duration Selection 1.5
output Levels I-5
External Trigger 1-5
External Duration l-5
Eunctions Available at Rear Connector l-6
Definitions Of Pulse Characteristics 1-6
Specifications 1~8
Performance Conditions l-8
SECTION 2 THEORY OF OPERATION 2-l
Introduction 2-l
Low Frequency Period Generator 2-l
4ns Period Generator 2.1
External Trigger Duration Buffer 2-I
Manual Trigger Multivibrator 2-2
Period and Trigger Out Buffers 2.2
Trigger Shaper 2-2
Duration Generator 2-2
Output Buffer 2-2
Output Driver 2"2
Output Amplifier 2-2
output Level Programmer 2.2
Power Supply 2-3
SECTION 3 SERVICE INFORMATION
Symbols and Reference Designators 3.1
Rear Interface Connector Assignments 2-2
Electrical Parts List 3-3
Internal Adjustment Procedure
Timing Board Parts Location Grid
Front Panel Controls and Connectors
Block Diagram
Output Board Parts Location Grid
Generators and Trigqer Schematic
Output Schematic
Switch Details and Power Supply Schematic
Mechanical Parts List
Exploded View
Accessories and Repackaging
m
PG 502
Section l-F% 502
OPERATING
INSTRUCTIONS
INTRODUCTION
Instrument Description The front panel is color coded for easy reference to
controls and their associated functions. Orange denotes
The PG 502 is a 250 MHz general purpose pulse genera-
pulse duration controls and settings; green. `triggering
tw for use in the TM 500 series power modules. Major
functions; and yellow is used for an operating caution note.
capabilities of this instrument include high repetition rate,
Alpha-numerics done in red are the frequency equivalents
narrow pulse width, fast risetime, and independent pulse for the pulse period settings.
top and bottom level controls. Front panel controls provide
manual trigger, square wave output, and complementary
pulse output for high duty factors. Installation and Removal
The PG 502 is calibrated and ready for use when
received. It operates in any compartment of a TM 500
A selectable 50 11 back termination in the pulse output series power module. See the power module instruction
circuitry is also provided. All other inputs and outputs are manual for line voltage requirements and power module
internallv terminated in 50 fl. operation. Fig. 1-l shows the installation and removal
procedure. Check that the PG 502 is fully inserted in
the power module. Pull the power switch on the power
module. The POWER light on the PG 502 front panel
Triggers preceding the output pulse are available at the should "ow be on. Refer to the Controls and Adjustments
fr'ont panel. The pulse output may also be externally foldout page in Section 3 of this manual, for a complete
triggered. description of the front panel controls.
Operating Instructions-PG 502
I.
OPERAT `ING CONSIDERATIONS I
Q
Output Terminations arid Connections
The output of the PG 502 operates as a 100 mA current
reflections. For maximum fidelity. use ths special three
foot long 50 .Q coaxial cable with special BNC connectors
supplid %s % standard `accessory (Tektronix Part No.
I
source. It is designad to operate into an external 50 $I load. 012-0482-00). Us% the internal back termination whenever
An unterminated
aberrations
or improperly terminated
Loads less than 5Ofi reduce the pulse amplitude.
output causes
on the output pulse (see Impedance Matching).
Loads
oossible.
I
greater than 50 $1 increaae the amplitude. An external 50 $2 When signal comparison tne%sur%ments or time differ.
load also urovides a DC return path for the output current. ence determinations are made, the two signals from the test
device should travel through coaxial cables with identical
10s~ and time delay characteristics.
I
A selectable 50 .S2back termination is provided [pull the
button tabled BACK TERM (PULL) on the front panel].
The back termination
output v&age
also helps to absorb reflections. The
is divided by two when using the back
Make certain the attenuators
safely handle the maximum
and terminations used can
PG 502 power output of
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termination. The back termination provides the DC return 0.5 Watts.
path for the outp,ut when driving high impedance or
capacitively-coupled loads. If the output of the PG 502
drives a high impedance load using the back termination, When making connections that %re not in a 5Ofi
the output voltage is limited to approximately f5 V. environment, keep all lead lengths short, l/4 inch or lass.
Accessory filters to increase risetimes and reduce the need
for high quality attenuators and terminations are'available.
I
A DC current in the 50 51 output load CBUSS the output
See your Tektronix Representative for more information.
pulse to be offset.. Do not apply voltages greater than plus
or minus 5 V to the output of the PG 502. If the load has %
DC voltage across it greater than the maximum allowed,
I
connect a blocking capacitor in series with the OUTPUT
connector and the load. Us% the back termination
provide a PC return path for the output current. Make
certain the time constant of the capacitor and the load is
to Impedance Matching
A mismatch, or different impedance in a transmission
el
line, generates a reflection back along the line to the source.
I
large enough TO, maintain pulse flatness. The output
The amplitude and polarity of the reflection ar% determined
circuitry of the PG 502 is fully protected against any
by the load impedance in relation to the characteristic
voltage transients in the output resulting from passive loads.
impedance of the cable. If the load impedance is higher
than the characteristic impedance of the line, the reflection
Under cenain conditions,
PG 502 into a high impedance
it is possible to operate the
load without using the
will be of the wna polarity as the applid
lower, the reflection
reflections
signal. If it is
will be of opposite polarity.
add or subtract from the amplitude
These
of the
I
internal termination. Pulse amplitudes up to about 18 V
incident pulse causing distortion and irregular pulse shapes.
(-9 V to +9 VI can be obtained in this manner with load
impedances in excess of 180 .Q. The PG 502 is not specified
when operating in this mode. To we the instrument in this
A simple resistive minimum attenuation impdsncs-
I
manner, view the output with an oscilloscope while
adjusting the OUTPUT
waveform.
(VOLTS) control,s for the desired
matching network that can be used to match the PG 502
output into relatively low impedances is shown in Fig. 1-2.
To match impedances with the illustrated network, the
.I
following conditions must exist:
Maintaining Pulse Fideky
Due to the extremely fast pulse r$etimes obtained from
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the PG 502, special consideration must be given to prewva- (R, +q R,
tion of pulse fidelity. Even et low repetition rates, 1 GHz rm5t equal 2,
frequency components are pr%s%nt in the output waveform. Rl+z,*R=
Use high quality coaxial cables, %tt%nuators. and termina- and
tions.
I
RG 58 type coaxial cable and typical BNC connectors a
exhibit impedance tolerances which may cause visible
,I
I-2
1,
Operating Instructions--PG 502
Therefore:
A,
=
and
I R,
=
z,
For example; to match a 5Oa system to a 125R
system. Z, equals 50 s-1 and 2, equals 125 R.
I Therefore:
R, = 125(125 - 50) = 96.8 ohms,
The illustrated network ten be modified to provide
and different attenuation ratios by adding another resistor (less
than R,) between 2, and the junction of A, and R,.
R, = 50 f ,;;T50 = 64.6ohms.
When constructing such a device, the environment
surrounding the components should also be designed to
Though the network in Fig. 1.2 provides minimum provide smooth transition between the impedances. Accept-
w attenuation, for B purely resistive impedance-matching able performance can be obtained with discrete eompo-
device, the attenuation as seen from one does not equal rents using short lead lengths; however, a full coaxial
that wn from the other end. A signal (E, ), applied from environment is preferred.
,",,
!j the lower impedance source, encounters a voltage attenua-
tion (A,1 which is greater than 1 and less than 2, as
follows: The characteristic impedance of a coaxial device is
determined by the ratio between the outside diamter of the
inner conductor to the inside diameter of the outer
A, -Li=El+, conductor expressed as:
E2 *2
138
A signal (E2) applied from the higher impedance source Z, =F log, ,, D/d,
(Z,) encounters a greater voltage attenuation (A,1 which is
greater than 1 and less than 2(2,/Z, ):
The relative dielectric constant is e (e,,, = l), D is the
inside diameter of the outer conductor and d is the
diameter of the inner conductor.
Further information on attenuator design may be found
in Reference Data For Radio Engineers, Fifth Edition,
Howard W. Sams& Co. Ir~c., New York, N.Y.. Chapt. 10, or
In the example of matching 50 Q to 126 .Q, other suitable reference work.
96.8
A, = 125 + 1 = 1.77
Consider carefully the effects of impedance mismatches
or discontinuities in transmission lines and terminations.
and Short lengths of wire exhibit inductance causing pulse
aberrations. Use 50 fi environments or, if this is impossible,
96.8 96.8 keep ail lead lengths as short as possible (l/4 inch or
A, =64.6+50 + 1 =4.43
shorter).
1-3
If the QG 502 is driving the 1 Ma capacitively-shunted R, equals the overall rise or falltime of the entire
vertical input of a" oscilloscope, connect a 50 a termina- measurement system and R,, R,. R,, etc. are the risetimes
tion to the oscilloscope input. Connect the coaxial cable or falltimes of the individual componentc comprising the
from the PG 502 to a 50 a 10X attenuator, and connect system. - rrl
the attenuator to the termination. The attenuator isolates
I
the input capacity, providing a" improved termination for
the cable. Another method is to back terminate the PG 502 I
by pulling The BACK TERM (PULL) pushbutton on the Variable Pulse Delay
front panel, and connecting the coaxial cable to the
oscilloscope input through a 50 fi termination. Variable pulse delays may be obtained using another
PG 502, or other suitable pulse generator. For example,
using two PG 502s. push the COMPLEMENT button and,
using a" oscilloscope, set the OUTPUT (VOLTS) LOW
LEVEL control on rhe delay generator for 0 V. Set the
Risatima Measurements in Linear Systems
HIGH LEVEL control for +I V. Some fine luning of the
Consider the rise and fallfime of associated equipment output levels of this generator may be necessary to achieve
when measuring the rise or falltime of a linear device. If the 250 MHz operation. Connect the OUTPUT from the delay
risetime of the device tinder tesl is at least ten times slower generator to the +TRIE/DURATION INPUT connector on
than the combined risetimes of the QG 502. the monitoring the output. generator. Take the pulse output from the I
oscilloscope, and acsociated cables, the error introduced OUTPUT connection on the output generator, and the
will not exceed I%, and usually may be ignored. If the rise trigger from the + TRIG OUT connector on the delay
or falltime of the test device is less than ten times slower generator.
than the combined risetimes of the testing sysw", deter"
mine the actual risetime of the device under test by using
the following formula:
The PERIOD controls on the delay generator now set
the period of the output waveform, and the DURATION
controls set the delay. The output pulse duration and
I
voltage levels are set by the appropriate controls on the
R, = YH , + H 2 + R 3 output generator. See Fig. I-3
Instructions-PG 502
OPERATI NG MODES
Period and Duration Selection External Trigger
The period generator free runs at the rate 5et by the The period generator is disabled when the PERIOD
PERIOD selector and the PERIOW VARIABLE control in selector is in the EXT TRIG position. An external
all modes except SO WAVE and EXT DURATION. The positive-going signal applied to the TRIG/DURATION IN
duration of the output pulse is set by the PULSE connector, triggers the duration generator. The pulse
DURATION selector and its associated PULSE DURA. duration of the output pulse varies with the front"panel
TION VARIABLE control. The PERIOD and PULSE Pulse DURATION selector and VARIABLE CQtltlOl. The
DURATION selectors are mechanically coupled, so the period of the output waveform is the period of the
duty factor cannot exceed 50% with the VARIABLE triggering signal. See Fig. l"4. The external trigger signal
controls in the Xl positions. Under most circumstances. must remain above the recognition threshold for at lwst
duty factors far in except of the specified 50% may be 2 ns. It must also remain below the reset threshold for at
obtained in the NORM mode using the VARIABLE least 2 ns to reset the generator for the next trigger.
controls. Excessive duty factor is indicated by any of the
following pulse abnormalities: (1) pulse output period in
multiples of the trigger output period, and (2) alternate
pulses with durations less than the pulse duration setting.
Wuty factors approaching 100% may be obtained by
switching to the complement mode. Set the PULSE
DURATION control for a pulse width equal to thedesired
pulse off time and push the front panel COMPLEMENT (-1
pushbutton.
In the square wave mode, the duration is automatically
set to approximately 50% of the period setting.
Output Levels Entwnal Trigger Signal
The output amplitude and offset are selected by
independent pulse HIGH LEVEL and pulse LOW LEVEL
controls. Use the front panel voltage calibration marks
when the load resistance is 50 ti. and the back termination
is not. used. The output voltage is one half of the voltage
indicated by thedial calibration when the back termination
is used. The OUTPUT (VOLTS) controls are interlocked 50
that it is impossible to set the HIGH LEVEL control more A manual trigger is available for single pulse operation.
negative than the low level. It is also impossible fo set the Disconnect any external trigger input when not in use.
controls for more than about 5.5 V P-P outpuf amplitude
into 50 Il. Pulse amplitude always equals the pulse high
level minus the pulse low level. Offset may be the high level External Duration
or the low level, whichever is used as rhe baseline reference
level. The flexibility of this method of controlling the The period generator and duration generator are disabled
output amplitude and offset is useful in certain applications when the DURATION selector is in the EXT DURATION
such as logic testing, i.e.. cither the hiqh or low level can be position. A voltage exceeding the recognition level applied
varied wifhout disturbing the other. to the TRIG/OURATION INPUT connector will activate
the outpuf of the PG 502. The period and duration of the
output will depend on the period and duration of the
Use of the Inormal complement function allows inter- externally-applied voltage. See Fig. 1.5. When operating in
changing the pulse on-off times without varying the voltage this mode, the output of the PG 502 is activated as long as
ICVPIS. the MAN TRIG pushbutton is depressed
1-5
Operating Instrucfions-PG 502
Refer to the rear connector assignment illustration in the To obtain Trigger/Duration input capabilities at the rear
Service Section at the rear of this manual for suggested pin interface connector, remove the coaxial cable from the
assignments. These connections are not factory wired. front panel connetior and the coaxial corm&or on the I
Timing Board. Use a new piece of coax about ten inches
long with suitable connection. Solder the free end of this
cable to the rear interface pads located as shown in the I
To obtain a trigger out signal complementary to the illustration.
front panel trigger out pulse, connect one end of a coaxial
cable to the pads on the Timing Board marked Internal Trig
Out. Connect the other end to appropriate pins as shown in Remember, when planning to use the rear interFace I
the illustration. Connections made to the Infernal Trig Out connectors, pulse fidelity may be disturbed due to the
pads do not +erfere with the front panel f TRIG OUT impedance mismatch the signals are subjected to in passing
signals. A one-half volt signal into 50 fi is available at the through the connectors. I
Internal Trig Out pads.
A slot between pins 23 and 24 on the rear connector
identifies the PG 502 as a member of the signal source
To, obtain the + TRIG OUT signal at the rear interface family. A barrier may be inserted in the corresponding
connector, disconnect the coaxial cable from the front position of the power module jack to prevent other than
panel + TRIG OUT connector and the coaxial connector signal source plug-ins from being used in that compartment.
labeled Trig, Out on the Timing Board. Replace this cable This protects the plug-in should specialized connections be
with another 500 cable about ten inches long, with a made fo that compartment. Consult the Building A System
similiar coaxial ~nnector on one end. Solder the other end Section of the power malule manual for further informa-
to the holes located as shown in the illustration. tion.
DEFINITIONS OF PULSE CHARACTERISTICS
The following is a glossary of common pul~l characteris- Amplitude. The maximum absolute peak value of a
tics used in this manual. They are illustrated in Fig. 1.6. pulse measured from the baseline regardless of sign, and
Operating Instructions-PG 502
Pulre Period
T = ,/Rate
t--
Duly Facto* = Pulse DurationlPulsa Period
excluding unwanted aberrations or overshoot. Measurement High Level. The most positive value of a pulse, regard-
points are at 50% of the pulse duration time (pulse high less of unwanted aberrations or overshoot, measured at a
IevelJ and on rhe baseline (pulse low level) at 50% of rhe off point that is located at 50% of the pulse duration.
time (the pulse period minus the pulse duration).
Low Level. The most negative value of a pulse. regard-
Aberrations. Unwanted deviations or excursions in the less bf unwanted aberrations or overshoot, measured at a
pulse shape from an ideal ~uare corner and flat top, i.e.. point fhat is at 50% of the off time.
overshoot. undershoot or rounding, ringing, and tilf or
dope.
Offset. A DC potential of either polarity applied to the
waveform to bias the baseline to an amplitude other than
zero.
Baseline. The quiescenf DC voltage reference level of
the pulse waveform,
Overshoot. The short term'pulse excursion (0; tran-
si@nT) above the pulse top or below the baseline, which is
Complementary Pulse. Normal pulse with high and low simultaneous to the leading or trailing edge of the pulse.
levels inrerchanged. Pulse on-time becomes pulse off-time.
Period. The time interval for B full pulse cycle. inverse
Duty Factor. Sometimes referred to es duty cycle. The of frequency or repetition rate, or the interval between
ratio of pulse duration to period, or the product of pulse corresponding pulse amplitudes of two consecutive un.
duration and pulse repefifion rate. Duty fector in % = delayed or delayed pulses. Generally measured between the
Duration/Period X 100. 50% amplitude levels of two consecutive pulses.
Falltime. The time interval. et rhe pulse trailing edge, Preshoot. A transient excursion rhat precedes the Step
for the pulse amplitude to fall from the 90% amplitude function. II may be of the same or opposite polarity as the
level to the lOPA amplitude level. pulse.
Flatness. The absence of long rerm variations to the Pulse Duration. The time interval between the leading
pulse top; excluding overshoot. ringing or pulse rounding. and trailing edge of a pulse at which rhe instantaneous
Sometimes referred to a5 tilt or slope. amplitude reaches 50% of the peak pu,lse amplitude.
8 1-7
,Operating:I"9tructions--PG:502
m3
Polarity. The direction from the baseline of the pulse Rounding or Undershoot. The rounding of the pulse
excursio", either positiveqoing (+) or negativegoing (6). corners at the &es of a step function.
Ri"gin,g. Periodic aberrations that dampen in time,
following the overshoot.
Risetime. The time interval, at the step function Tilt or Slope. A distortion of e" otherwise flat~toppql
lesding edge, for the'pulse to rise from the 10% to the 90% pulse, characterized by either a decline or a rise of the pulse I
amplitude levels. top. (see Flatness). *
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SPECIFICATIONS
I
Performance Conditions Accuracv: 5% from 5 ns to .5 ms, 15% of 5 mr range,
with both period and duration variables in calibrated
The electrical characteristics ere valid only if the PG 502
positions. Duration may vary not more than 3% +
is calibrated at a" ambient temperature betwew+20*C and
0.5 ns for any duty factor less than 50%.
+30