Tektronix PG 506 User manual

Tektronoo
COMMITTED TO EXCELLENCE
PLEASE CHECK FOR CHANGE INFORMATION
AT THE REAR OF THIS MANUAL.
PG 506
CALIBRATION
GENERATOR
(S N 804 0000 AND UP)
INSTRUCTION MANUAL
Tektronix, Inc .
P.O.
Box 500
Beaverton, Oregon 97077 Serial
Number _____ _
070-3383-00 First Printing NOV 1980
Product Group 75 Revised DEC 1981

Copy ri ght ©1974 , 19 80 Tektr on ix, I nco All rights reserved.
Cont ents of this pub lic ation may not be reproduced in
anyform without th ewr itt en permissionof Tektronix, Inc.
Products
of Tektroni x, Inc. and its subsidiaries are
covered
by U. S. and foreign patents and/or pending
patent
s.
TEKTRONIX, TE K, SCOPE-M OB IL E, and . are
regi
ste>r ed trademarks of Tektronix, Inc . TELEQ UI P-
MENT is a registered trademark of T
ektronix U.K.
Lim
it ed.
Printed in U.S.
A. Specification and price change
privileges are reserved.

PG 506
(SN B040000 & up)
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS ..... . .. . . .. .... . . ii
LIST OF TABLES ... .. . . . . . . . . . .... . .. . ... . .
Secti
on 1 Specification . . . . . . . . . . . . . . . . .. 1-1
Section 2 Operating Instructions 2-1
I WA RNING I
THE FOLLOWING SERVICE INSTRUCTIONS ARE
FOR USE BY QUALIFIED PERSONNEL ONLY . TO
AVOID PERSONAL INJURY, DO NOT PERFORM
ANY SERVICING OTHER THAN THA T
CONTAINED IN OPERA TlNG INSTRUCTIONS
UNLESS YOU ARE QUALIFIED TO DO SO .
Section 3 Theory of Operation. . . . . . . . . . . . . 3-1
Section 4 Calibration Procedure . . . . . . . . . . .. 4-1
Performance Check . . . . . .. . .. . 4-3
Adjustment Procedure . . . . ... .. 4-12
Section 5 Maintenance ... .. . . ....... ... . 5-1
Section 6 Options .... .... .. . ....... . . . . 6-1
Section 7 Replaceable Electrical Parts . .. . .. . 7-1
Section 8 Diagrams and Illustrations ... .. ....
8-1
Section 9
Replaceable Mechanical Parts . . . .. . 9-1
@

PG 506 (SN 8040000 & up)
LIST OF ILLUSTRATIONS
Fig.
No. Page
PG 506 Calibration Generator. . . . . . . vi
2-1 Plug-in installation and removal ...... , 2-2
2-2 PG 506
controls and connectors ... . .. 2-3
2-3
Output signals from the PG 506 Calibration
Generator ........... . .......... 2-6
2-4 Risetime
derating graph ... . . . . . . . . . 2-7
2-5
Typical waveforms showing correct and
incorrect compensation adjustments ... 2-8
2-6
Typical low frequency response curve " 2-9
2-7
Distortion of square waves caused by low
frequency effects . . . . . . . . . . . . . . . .. 2-9
2-8
Typical waveform showing ringing at front
corner. . . . . . . . . . . . . . . . . . . . . . . . . 2-9
3-1 DVM
timing diagram for a negative input to
the integrator U460 . . . . . . . . . . . . . . .. 3-4
4-1 Attenuator connecti ons for current source 4-4
4-2
Typical response curve of sampling system 4-9
4-3
Typical sampling oscilloscope response
display .... . ..... . ...... . ...... 4-10
4-4
Typical sampling oscilloscope response
display . ....... . ............... 4-10
4-5
Adjustment locations for the A1 Main
circuit board ................... . 4-13
4-6
Adjustment locations for the A2
DVM/Period circuit board ......... . . 4-14
4-7
Adjustment locations for the A3 Fast Rise
Output circuit board. . . . . . . . . . . . . .. 4-16
4-8
Typical response curve as displayed on the
sampling system . . .......... . .... 4-17
4-9
Typical response curve as displayed on the
sampling oscilloscope . ............ . 4-17
5-1 Pin assignments for the PG 506 (rear view,
partial) . . . .
.... . ...... .. ....... 5-3
5-2 Main interface board (partial)
showing
connections. . . . . . . . . . . . . . . . . . . .. 5-4
amplitude and trigger output cable
ii @

PG 506 (SN 8040000 & up)
LIST OF TABLES
Table
No .
1-1
1-2
1-3
2-1
4-1
4-2
4-3
4-4
4-5
4-6
5-1
5-2
@
Electrical Characteristics. . . . . . . . . ..
Environmental Characteristics . . . . . ..
Physical Characteristics . . . . . . . . . ..
Output Load Vs . Voltage Out . . . . . . . .
Test
Equipment Required. . . . . . . . . .
Standard Amplitude (into 1 MO) Within
0.25%, ±1 jN . . . . . . . . . . . . . . . . . ..
100 V dc Range DEFLECTION ERROR %
Resolution Tolerances ... ... .. . . ..
10 V dc Range DEFLECTION ERROR %
Resolution Tolerances .... . ..... . .
Standard Amplitude into a 50 0 Load..
Fast Rise and High Amplitude Output
Period. . . . . . . . . . . . . . . . . . . . . . ..
Selected Component Criteria . . . . . . . .
Relative Suscepti bility to Static Discharge
Damage. . . . . . . . . . . . . . . . . . . . . ..
Page
1-1
1-3
1-3
2-5
4-1
4-3
4-5
4-5
4-5
4-7
5-1
5-5
iii

iv
PG 506 (SN 8040000 &up)
OPERATORS SAFETY SUMMARY
The general safety information in this part of the summary
is for both operating and servicing personnel. Specific
warnings and cautions will be found throughout the
manual where
they apply, but may not appear in this
summary.
TERMS
In This Manual
CAUTION statements identify conditions or practicesthat
could result in damageto the equipment or other property .
WARNING statements identify conditions or practices
that
could result in personal injury or loss of life.
As Marked on Equipment
CAUTION indicates a personal injury hazard not im-
mediately accessible as one reads the marking, or a
hazard to
property including the equipment itself.
DANGER indicates a personal
injury hazard immediately
accessible as one reads the marking.
SYMBOLS
In This Manual
This symbol indicates where applicable
cautionary or other information is to be
found.
As Marked on Equipment
DANGER - High voltage.
Protective
ground (earth) terminal.
ATTENTION -refer to manual.
Power Source
This product is intended to operate from a power source
that will not apply more than 250 volts rms between the
supply conductors or between either supply conductor
and ground. A protective ground connection by way of the
grounding conductor in the power cord is essential for
safe operation.
Grounding the Product
This product is grounded through the grounding conduc-
tor of the power cord. To avoid electrical shock, plug the
power cord into a properly wired receptacle before
connecting to the product input or output terminals. A
protective
ground connection by way of the grounding
conductor in the power cord is essential for safe opera-
tion.
Danger Arising From Loss of Ground
Upon loss of the protective-ground connection , all
accessible
conductive parts (including knobs and con-
trols that may appear to be insulating) can render an
electric shock.
Use the Proper Fuse
To avoid fire hazard, use only the fuse of correct type,
voltage rating and
current rating as specified in the parts
list for
your product.
Refer fuse replacement to qualified service personnel.
Do Not Operate in Explosive Atmospheres
To avoid explosion, do not operate this product in an
explosive
atmosphere unless it has been specifically
certified for such operation .
Do Not Operate Without Covers (for TM 500 plug-
ins only)
To avoid personal injury, do not operate this product
without covers or panels installed. Do not apply power to
the plug-in via a plug-in extender.
@

PG 506 (SN 8040000 & up)
S ER VI CE SAFETY SUMMAR Y
FOR QUALIFIED SERVICE PERSO NN EL ONLY
Re fer a/so to the preceding Operators Safety S ummary.
Do Not Service Alone
Do not perform internal service or adjustment of this
product unless another person capable of rendering first
aid and resuscitation is present.
Use Care When Servicing With Power On
Dangerous voltages exist at several points in this product.
To avoid personal injury, do not touch exposed connec-
tions and components while power is on.
@
Disconnect power before removing protective panels,
soldering, or replacing components.
Po wer Source
This product is intended to operate from a power source
that will not apply more than 250 volts rms between the
supply conductors or between either supply conductor
and ground. A protective ground connection by way of the
grounding conductor in the power cord is essential for
safe operation.
v

vi
PG 506 (SN 8040000 & up)
faA CALIBRATING
INTO 50 II USE
10V TO 0 2mV
AND DIV I DE
VOLTAGE BY 2
HIGH
PG 506 CALIBRATIDN GENERATOR
DEflECTI DN ERRDR
1740 - 01
PG 506 Calibration Generator
@

Section 1-PG 506 (SN B040000 & up)
SPECIFICATION
Performance Conditions Items
listed in the Performance Requirements column
The electrical characteristics are valid only if the
of the Electrical Characteristics are verified by completing
PG 506 has been calibrated at an ambient temperature
the Performance Check in the Service Section of this
between
+20
0 C and
+30
0 C and isoperating at an ambient manual.
Items listed in the Supplemental Information
temperature between O°C and
+50°C. Forced air circula-
column are not verified in this manual. They are either
tion is required for am bient temperatures above +40
0
C.
explanatory notes or performance characteristics for
which no limits are specified.
SPECIFICATION
Table 1-1
ELECTRICAL CHARACTERISTICS
Characteristics Performance Requirements Supplemental Information
STANDARD AMPLITUDE OUTPUT
Range (Peak-to-Peak)
1 MQ Load
Accuracy
500 Load
Accuracy
Period
200 IN to 100 V
Within 0. 25% ± 1 jJV
100 jJV to 5 V
Within 0.25% ±1 jJV
Approximately 1 ms
(1 kHz square wave,
chopped DC)
Deflection Error Readout
Range
Resolution
+ and -
7.5%
Within 0. 1%
HIGH AMPLITUDE OUTPUT
Amplitude (Peak-to-Peak)
Unterminated
500 Load
Polarity
~ 6 V to :;:60 V
~ 0.5 V to :;:5 V
Positive,
measured from a negative
potential to ground .
1·1
REV DEC 1981

1-2
Specification-PG 506 (SN 8040000 & up)
Table 1-1 (cont)
, Characteristics
600 0
Output Resistance
Output Period
1
JiS to 10 ms
Variable
Duty Cycle
Rise Time
Unterminated
500 Load
Leading Edge
Aberrations
during first 50 ns
Performance Requirements Supplemental Information
Within 5%
Within 5%
Extends output period to at least 100 ms.
X1 to greater than X10 range for each
decade step.
Approximately 50% .
~ 100 ns
~ 10 ns
Within 2% of Signal peak-to-peak
amplitude, or 50 mV, whichever is
greater.
FAST RISE
OUTPUTS
Amplitude (Peak-to-Peak)
500 Load ~
100 mV to > 1 V
Polarity
Simultaneous positive and negative.
Positive is measured from a negative
potential to ground. Negative is
measured from a positive potential to
ground .
Output Resistance, 50 0
Within 3% At either Fast Rise connector.
Risetime, 50 0 Load ~
1 ns
Leading Edge
Aberrations ,
first 10
ns
Within 2% of Signal peak-to-peak
amplitude, or 10 mV, whichever is
greater.
Flatness
Within 0. 5% after first 10 ns
Output Period 1 s to 10 ms In decade steps.
Accuracy Within 5%
Variable Extends output period to > 100 ms. X1 to
greater than X10 range for each decade
step .
Duty Cycle Approximately 50%.
TRIGGER OUTPUT
+ Trigger Out ;::: 1 V peak-to-peak into a 50 0 load. Trigger out function available for HIGH
Fixed amplitude . AMPL and FAST RISE modes. Output Signal
leads
HIGH AMPL pulse by about 18 ns and
leads FAST RISE pulse by
about 8 ns.
REV DEC 1981

Specificalion-PG 506 (SN 8040000 & up)
Table 1-2
ENVIRONMENTAL CHARACTERISTICS
Characteristics Information
Temperature Test
to procedures of MIL-STD-810C Methods 502.1 and 501.1
using
Procedure I as specified in MIL-T-28800B paragraph 4.5.5.1.3 and
4.5.5.1.4.
Operating 0° C to +50 °C.
Non-operati ng -55
0 C
to + 75° C.
Humidity
Operating + 50° C to 95% relative humidity.
Non-operati ng + 60° C to 95% relative humidity.
Test to MIL-STD-810C Method 507.1 Procedure IV, modified as specified
in MIL-T-28800B paragraph 4.5.5.1.1. 2.
Altitude
Test to MIL-STD-810C Method 500.1
Procedure I as specified in MIL-T-
28800B paragraph 4.5.5.2.
Operating
To 15 ,000 feet.
Non-operati ng To 50,000 feet.
Vibration
Operating and
Non-operating With the instrument operating, the vibration frequency is swept from
10 to 55 to 10 Hz. Vibrate 15 minutes in each of the three major axes
at 0.015" total displacement . Hold 10 minutes at any major resonance ,
or if none, at 55 Hz. Total time , 75 minutes .
Shock
Non-operat ing 30 g's 1/2 sine, 11 ms duration, 3 shocks in each direction along 3
major axes, for a total of 18 shocks.
Transportation
Qualified under National Safe Transmit Committee Test Procedure 1 A,
Category II.
Table 1-3
PHYSICAL CHARACTERISTICS
Characteristics Information
Maximum Overall Dimensions
Height
Width
Length
4.969
inches (12.621 cm).
2.638
inches (6.701 cm).
12.088
inches (30.704 cm).
Front Panel
Finish
Anodized aluminum .
Net
Weight
= 2 Ibs. 4 oz. (1.02 kg).
@ 1-3

Section 2-PG 506 (SN 8040000 & up)
OPERATING INSTRUCTIONS
INTRODUCTION
Description
The PG 506 Calibration Generator is designed to
operate in a TM 500 Series Power Module. Theinstrument
is a combination Amplitude Calibrator and Square Wave
Pulse
Generator intended for cali bration and adj ustments
of oscilloscope amplifier systems with a 500 or 1 MO
input resistance.
The
Amplitude Calibrator function provides either a +
dc voltage or a 1 kHz square-wave output, as selected by
an internal switch. Peak-to-peak amplitudes from 0.2 mV
to 100 V across a 1 MO load and amplitude of 100 mV to
5 V across a 50 0 load are available. Output amplitudes
are selected ina 1,2,5 sequence.
Because errors are
often stated as a percentage, an
internal
digital differential voltmeter with front-panel light-
emitting diode (LED) readout is used to provide a display
equal to oscilloscope vertical or horizontal deflection
errors . If the indicated deflection on an oscilloscope
graticule does not agree with the proper reference Ii ne, the
output amplitude from the PG 506 Amplitude Calibrator
can be varied until the proper alignment is obtained.In this
operating mode, the front-panel readout is a direct display
of the oscilloscope deflection error.
@
A 5 mA Current Loop is provided, which supplies
current (dc or 1 kHz) for calibration of current probes.
The Pulse Genercitor
provides three square-wave out-
puts: variable High Amplitude pulses and simultaneous
positive and negative-goi ng Fast Rise, vari able-amplit ude
pulses.
In the Pulse Generator mode, the Period is
selectable
from 1 J.lS to 10 ms in decade steps. A variable
control extends the maximum period to at least 100 ms
(for each decade step,
the period is variable over a 10 :1
range). A
positive going pretrigger output is also provided
for triggering external equipment.
Installation and Removal
~
Turn the power module off before inserting the plug-
in; otherwise, damage may occur to the plug-in
circuitry. Because of the high current drawn by the
PG 506, it is also recommended that the power
mOdule be turned off before removing the PG 506.
Refer
to Fig. 2-1. Check to see that the plastic
barriers on the interconnecting jack of the selected
power module compartment match the cut-outs in
the PG 506 circuit board rear edge connector.
2-1

2-2
Operating Instructions-PG 506 (SN 8040000 & up)
POWER
MODULE
PLUG-IN
Bottom
Groove
Fig. 2-1. Plug-in installation and removal.
(1431-21) 1632-02
CONTROLS AND CONNECTORS
(2) DEFLECTION ERROR %: A direct display of output
amplitude deflection error.
CD
AMPLITUDE: Selects calibrated output amplitudes
across 1 MO or 500 load attached to AMPL OUT-
PUT (STD) connector .
CD
VARIABLE (OUT): When released, operates in the
standard
amplitude mode. The deflection error
readout indicates the error in percentages with 0.1%
resolution.
PERIOD light:
Illuminated when the function switch
is in Fast Rise or High Ampl mode .
PERIOD: Selects the
period of either the Fast Rise or
High Ampl square-wave signals.
® VAR: Extends the period range 10:1. The calibrated
position is counterclockwise.
(j) +TRIG OUT: Provides a signal source to pretrigger
external equipment.
FAST RISE OUTPUTS: Provides for simultaneous
positive and negative going square-waves as
selected
by the PERIODIVAR controls.
Function switch: Determines whether the instru-
ment is operated in STD AMPL, HIGH AMPL, or
FAST RISE mode.
@ PULSE
AMPLITUDE: Controls output amplitude in
the High Amplitude or Fast Rise modes.
®
AMPL OUTPUT HIGH or STD: Common output for
High Amplitude or Standard Amplitude modes.
1 kHz
square-wave or dc for Standard amplitude.
Period of the High Amplitude square-wave is set by
the Period controls.
® Current Loop: A dc or 1 kHz square-wave 5 mA
current supply for calibration of current probes . The
@

Operating Instructions-PG 506 (SN B040000 & up)
C~U8RATION GfNEAATOA
3383·03
Fig. 2-2. PG 506 controls and connectors.
@ 2-3

2-4
Operating Instructions-PG 506 (SN 8040000 & up)
VARIABLE (OUT) control will vary current through
the loop, but DEFLECTION ERROR readout is not
directly related to current deviations. The DEFLEC-
TION ERROR readout must be off or adjusted to
read 0.0% for a calibrated output.
Release Latch: Pull to remove the instrument from
the power module.
I WARNING I
Dangerous voltage may be present on the front-
panel BNC connector labeled AMPL OUTPUT
(HIGH or STD). Before installation, turn the control
labled AMPLITUDE (VOLTS INTO 1 MO.) fully
counterclockwise (ccw) and the control labeled
PULSE AMPLITUDE to MIN.
Align the upper and lower groove of the PG 506 chassis
with the upper and lower guides of the selected compart-
ment. Push the module in and press firmly to seat the
circuit board in the interconnecting jack.
To remove the PG 506, pull on the release latch located
in the lower left corner until the interconnecting jack
disengages and the PG 506 will slide out.
Preliminary Checks
Make all desired connections to equipment under test
before applying power to the PG 506. The power switch is
on the Power Module. Power
application to the PG 506 is
indicated by the PERIOD light turning on, or the light
behind the knob skirt of the AMPLITUDE control switch
being lighted .
The
front-panel LED can be tested (888 display) by
setting the three-position Mode switch to STD AMPL
position, then
pushing and holding the VARIABLE knob
concentric with the AMPLITUDE switch.
To test the digital voltmeter system, release the
VARIABLE knob to the out position and rotate the control
in both directions.
Allow 15 to 20 minutes warmup time for all equipment
before using the PG 506.
AMPLITUDE CALIBRATOR MODE
Connections and Terminations
To use the PG 506 Amplitude Calibrator system, set the
mode switch to the STD AM PL position. Connect the
1 kHz
calibrated amplitude signal at the AMPL OUTPUT
connector to the input of an oscilloscope through a
coaxial
cable that has a 500. characteristic impedance
(RG-58/U) with a maximum length of 42 inches (shorter
cables can be used).
With a cable termination of 1 Mo. and the DEFLECTION
ERROR display off, the 1 kHz signal peak-to-peak output
amplitude will be equal to the indicated reading on the
AMPLITUDE switch . If the cable is terminated into a 500.
load, use an output amplitude in the 10 V to 0.2 mV range;
the
output amplitude will then be one-half the indicated
reading on the AMPLITUDE switch .
Oscilloscope Controls
The deflection factor (either vertical or horizontal) for
oscilloscopes is the ratio of the amplitude of the input
signal to the amount of beam deflection produced on the
cathode-ray tube (crt), usually stated as volts per division
of deflection (Volts /Div). Calibration procedures for some
oscilloscopes require that the gain be set and the deflec-
tion accuracy be checked with a probe (properly compen-
sated) connected between the PG 506 and the os-
cilloscope input connector.
For oscilloscope gain adjustments and checking of
deflection accuracies, it is always best to set all os-
cilloscope controls exactly as called out in the calibration
and performance sections of the oscilloscope instruction
manual. However, it may be found desirable to set the
oscilloscope sweep controls to a 0.1 ms /div (or faster)
sweep rate and free-run the sweep
when performing
vertical deflection (amplitude) checks and adjustments.
This procedure produces two horizontal traces that are
separated
vertically by an amount proportional to the
peak-to-peak amplitude of the 1 kHz square-wave from
the PG 506. At faster sweep rates, the display becomes
more readable.
Deflection Error Readout
When performing gain adjustments on oscilloscope or
amplifier systems, it is mandatory that the DEFLECTION
ERROR readout be turned off in order to obtain calibrated
output amplitudes. The PG 506 DEFLECTION ERROR
readout
feature finds its greatest use in its ability to allow
an operator to verify the oscilloscope deflection accuracy
associated with amplifier gain and input attenuators.
@

Operating Instructions-PG 506 (SN 8040000 & up)
Gain adjustments for oscilloscope amplifiers are usual-
ly made at low levels, for example; at a 10 mV/div
deflection factor and a 50 mV signal from the PG 506. This
ratio corresponds to five major graticule divisions of beam
deflection . If the gain of the oscilloscope amplifier system
is low,
the indicated deflection will be less than five major
graticule divisions, for example; 4.8 major division . The
VARIABLE AMPLITUDE (OUT) control on the PG 506 can
then be used to increase the output amplitude until the
total
deflection is exactly five major divisions. At this point,
the DEFLECTION ERROR readout will read 4.0% LOW.
Conversely,
if the oscilloscope amplifier system gain is too
high, the indicated deflection on the crt will be above the
proper reference line, for example; 5.2 major divisions.
Using the VARIABLE AMPLITUDE control on the PG 506
to reduce the output ampliutde for exactly five major
divisions of deflection will produce a DEFLECTION
ERROR readout of 4. 0% HIGH .
For
some oscilloscopes the deflection factor may not
be constant throughout the full vertical dimensions of the
graticule, due
to compression or expansion nonlinearities.
To check for this type of nonlinearity; center a two-
division display, then position the display to the top of the
graticule. Measure any deflection errors with the PG 506
VARIABLE AMPLITUDE control. Next , position the two-
division display to the bottom of the graticule and measure
the deflection errors. These nonlinearities should be taken
into account when making measurements with full
graticule deflection, or with the crt trace positioned
towards the top or bottom graticule limits and using small
deflection factors.
Current Loop
One end of the Current Loop is grou nded and ter-
minates a precision voltage divider. The direction of the
arrow is
oriented for conventional current. To obtain a
calibrated 5 mA from the Current Loop , set the mode
switch to STD AMPL position and the AMPLITUDE
control switch to the 100 V position. The DEFLECTION
ERROR readout should be off, or adjusted to read 0.0%.
The current signal can be either dc or 1 kHz square-wave
current,
as selected by an internal switch.
PULSE GENERATOR MODE
General
In order to ensure waveform fidelity when using the
Pulse Generator function of the PG 506, the following
precautions should be observed.
1. Use high quality 500 coaxial cable , connectors,
and terminations (where applicable). Make all connec-
tions as tight and short as possible.
@
2. Reduce capacitive and inductive loads to a
minimum. Risetime degradation occurs with long cable
lengths .
3. Minimum risetime and pulse aberrations are ob-
tained
with 500 loads and loads must be capable of
dissipating the power available at any output connector in
any operating mode.
4. The external equipment is assumed to have no dc
voltage across the load to which the PG 506 is connected.
If a dc voltage exists, the output amplitude from the
PG 506 will be in error by the amount of the dc offset. To
prevent dc-offset errors, couple the PG 506 outputs
through a dc blocking capacitor to the load. The time
constant of the coupling capacitor and the total resistance
in series must be long enough to maintain pulse flatness.
High Amplitude Output
To use the PG 506 Pulse Generator system to produce
high amplitude square-waves, set the mode switch to
HIGH AMPL pOSition and connect external equipment to
the AMPL OUTPUT HIGH connector. Set the Period
controls for the period or frequency desired. The output
amplitude of this signal can be adjusted with the PULSE
AMPLITUDE control.
This signal can be used to adjust oscilloscope amplifier
input capacitance , attenuator compensation networks,
and
other internal frequency compensation networks. The
AMPL OUTPUT HIGH signal is negative with respect to
ground , with its risetime related to the riSing portion (from
a negative potential) of the waveform. Refer to Fig. 2-3.
The absolute peak-to-peak val ue of the square-wave is
determined by the load resistance and the setting of the
PULSE
AMPLITUDE control. Table 2-1 lists the typical
amplitudes available when the PG 506 is terminated into
three different load resistances.
Table 2-1
OUTPUT LOAD VS. VOLTAGE OUT
HIGH AMPL OUTPUT PULSE AMPLITUDE Control'
Termination MIN
MAX
500 Load 0.3 V p-p 5.2 V p-p
6000 Load 1.9 V p-p
32.5 V p-p
1 MO Load
3.8 V p-p
~ 60.0 V p-p
'Approximate amplitudes.
2-5

Operating Instructions-PG 506 (SN 8040000 & up)
REFERENCE EDGE
;;;' 1 V
+TRIG
~
FIXED
OUT
AMPLITUDE
__ 0 V
REFERENCE EDGE
- -fO V
HIGH
-t
AMPLITUDE
VARIABLE
SQUARE WAVE
REFERENCE EDGE
)
FAST RISE
~
OUTPUT
REFERENCE EDGE
FAST RISE
-~
-r
OUTPUT
1740-02
Ag. 2-3. Output signals from the PG 506 Calibration Generator.
Fast Rise Outputs
To use the PG 506 Pulse Generator system to produce
low amplitude , fast-rise square-waves, set the mode
swtich to FAST RISE position and connect external
equipment to the FASTRISE OUTPUTS connector(s) . Set
the PERIOD
controls for the period or frequency desired.
The
output amplitude can be adjusted by the PULSE
AMPLIUTDE control.
These signals are
usually used to adjust high-
frequency compensation networks in oscilloscope
amplifier circuits. The adjustments are made for optimum
response (minimum aberrations). The risetime and
amplitude specifications for the FAST RISE outputs apply
only when they are terminated into a 500 load. Larger
amplitudes (greater than 1 V peak-to-peak) can be ob-
tained from these
output connectors under unterminated
conditions, but the risetime specification is no longer
applicable.
GENERAL INFORMATION
Risetime Considerations
The PG 506 can be used in conjunction with an
oscilloscope to determine the risetime of a device under
test. Risetime is
normally measured (unless otherwise
specified) between the
10% and 90% amplitude levels on
2-6
the leading edge of a waveform. The risetime of a
displayed waveform is
illustrated in Fig. 2-4.
Before
measuring the risetime of a device under test,
the
combined risetime of the PG 506 output signal and the
oscilloscope vertical amplifier system must be known.
Refer
to Fig. 2-4 for the percentage error to be expected
when the two devices are cascaded. Sweep timing ac-
curacy should be verified before any risetime measure-
ments are made.
Inaccuracies in the sweep timing and
display reading errors must be added algebraically to the
percentage error obtained from computations related to
Fig. 2-4.
The
graph for Fig. 2-4 can be used as a guideline for the
following general conclusions.
1. Oscilloscopes should have a vertical system
risetime
about one-seventh of the fastest signal applied to
keep system errors to a minimum.
2. Conversely, if the signal risetime is at least seven
times faster
than the risetime of the oscilloscope vertical
system, the displayed (observed) waveform
will have a
risetime
that is very close to the risetime of the vertical
system.
3. The displayed risetime as observed on any os-
cilloscope can never be faster than the risetime of the
slowest device in the system.
Risetime of a displayed waveform is related
to total
system
bandwidth . A system with limited high-frequency
response will produce a displayed risetime that is slower
than expected. If a fast-step signal produces a crt display
with little or no overshoot or ringing, the product of
oscilloscope risetime and oscilloscope bandwidth should
result in a factor whose value lies between 0.329 and 0.350.
The
followi ng steps describe the procedure to follow in
determining the risetime of a device under test.
1. Connect the appropriate output signal from the
PG 506 to the oscilloscope vertical input with ashort 500
coaxial cable terminated into a 50 0 load.
2. Set the
oscilloscope controls to display the leading
edge of the waveform. Risetime measurements should be
made over
the largest part of the graticule area possible.
When
the fastest sweep rate is relatively slow compared
with the vertical system risetime (or the scale is small),
measurements become
confined to small sections of the
graticule, and the probability of display reading errors
becomes greater .
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Operating Instructions-PG 506 (SN 8040000 & up)
40
I",
30 " APPLIED STEP
FUNCTION
25
pos~
20
GOING
",
15
OBSERVED WAVEFORM
"
100% _______
w
90%------
,
~
I
I
1\..
f= 10
" -I
w I
!:!?
9
10 % ---
I
a:
0%
I I
-'.. , :-RISETIME
l-
S
w
Z 7
u..
0 6 "
w
II)
< 5
"'
'-...
w
a:
(J
! 4
I-
Z
OSCILLOSCOPE
w PG 506
(J
"
1 ns
3
w
a:
c. 0
0 "
T I
~
2
'"
",
2 3 4 5 6 7
RATIO OF RISETIMES
Rg _ 2-4_ Risetime derating graph_
3. Measure the time duration between the 10% and
90% amplitude levels. This is the combined risetime of the
PG 506 and the oscilloscope (Trc).
4.
Disconnect the coaxial cable and 50 0 termination
from the oscilloscope .
5. Connect the coaxial cable from the PG 506 to the
input of the device under test and connect the output of
@
the device under test to the oscilloscope vertical input.
Terminate the device under test in its characteristics
impedance for optimum performance.
6. Set the oscilloscope controls to display the leading
edge of the displayed waveform and measure the time
duration between the 10% and 90% amplitude levels (over
the same graticule area, if possible). This is the total
system risetime (T ,, ).
1740 - 03
2-7

2-8
Operating Instructions-PG 506 (SN 8040000 & up)
7. Calculate the risetime of the device under test (dut)
using the following formula:
1/ 2
T, (dut)
Checking Amplifier Response
The square-wave output signals from the PG 506 can
be used
to check the response of active or passive sys-
tems. Because
the characteristics of a pulse from the
PG 506 is known (see ELECTRICAL CHARACTERIS-
TICS), distortion of the waveform beyond these limits is
due to the device under test.
159 X 10-)
FL (3 dB) RC
For example;
if the applied frequency, F" is 10 Hz and the
amplitude values shown in Fig.2-6 are used, the lower cut-
off frequency is calculated to be about 1.6 Hz.
Figure 2-7 illustrates other waveform distortion effects
that may be observed if amplifier circuits are not properly
compensated for low frequencies.
The compensation of an ac-voltage divider, such as
used in the input attenuator of an oscilloscope or a passive
attenuator probe , can be checked by observing its
response
when a square-wave signal is applied . Correct
response is shown by optimum square corner on the
displayed waveform. If
the waveform has overshoot ,
rolloff,
or front-corner rounding, the system is not correct-
ly compensated. Figure 2-5 shows typical waveforms
illustrating correct and incorrect compensation ad-
justments. When
performing these compensation checks,
the repetition rate of the applied square-wave signal
should be at least 3 to 4 decades above the low-frequency
cutoff point (frequency where the equivalent si ne-wave
amplitude is 30% down) .
The low end cut-off frequency (due to RC coupli ng) for
an amplifier can be approximated very closely by usi ng the
following procedure.
1. Apply a square-wave at a repetition rate that is not
affected by the low-frequency limit.
2. Slowly reduce the square-wave frequency and
adj ust
the oscilloscope (amplifer) controls to display a
signal
similar to Fig. 2-6.
3. Determine the ratio between the amplitude levels, VI
and V2. Note that VI and V2 are peak val ues above the zero-
volt reference level.
4. The equivalent RC product can be determined by
using the following formula; where F, is the applied
frequency for a given ratio of VI 1V
2 (greater
than unity).
= RC (for square-waves only)
5. Using the RC product obtained in step 4, calculate
the low-end cut-off frequency.
-
- II
;.-
A. Overshoot and top not flat.
!
r--
f+++--
:+ 11
H-H
r- H-H- i i t-l -'-+++-
f-'--'++ -
I
---
'--
B. Correct compensation (square corner, flat top).
-I
-""-
t'
V -
+ H -t-
tt-H
++++
I+H +
..
H-J-t- -t- .. !-t-.-+H-
'--- .,-
--
C. Rollo!! and top not flat.
1740 · 04
Fig. 2-5. Typical waveforms showing correct and incorrect
compensation adjustments.
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