Tektronix FG503 User manual

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BEFORE READING
070-1727-00
PLEASE CHECK FOR CHANGE
INFORMA TION
AT THE REAR OF THIS MANUAL .
THIS MANUAL REPRINTED FEBRUARY
1978
FG
503
FUNCTION
GENERATOR
INSTRUCTION
MANUAL
Tektronix,
Inc .
P
.O .
Box500
Beaverton, Oregon 97005

Serial Number
First Printing
APR 1974
TEKTRONIX° I
Z 1
A
9
,,

TABLE
OF
CONTENTS
SECTION 1

OPERATING INSTRUCTIONS

Page
Introduction

1-1
Instrument Description

1-1
Initial Operation

1-1
Functions Available At Rear Connector

1-2
Operating Considerations

1-2
Output Connections

1-2
Risetime and Falltime

1-2
Impedance Matching

1-2
Basic Operation

1-4
Free-Running Output

1-4
Voltage-Controlled Frequency
(VCF) Output

1-4
Custom Timing Capacitor Selection

1-5
Typical VCF Application

1-6
Electrical Characteristics

1-7
Repackaging for Shipment

1-8
SECTION 2

THEORY OF OPERATION
Introduction

2-1
Triangle Generator

2-1
Sine Shaper

2-1
Output Amplifier

2-2
Power Supplies

2-2
SECTION 3

SERVICE INFORMATION
Symbols and Reference Designators

3-1
Electrical Replaceable Parts List

3-2
Front Panel Controls and Connectors
Calibration Procedure
Services Available
Maintenance
Test Equipment
Parts Location Grid
Rear Interface Connector Assignments
Block Diagram
Generator Loop Schematic
Output Amplifier Schematic
Power Supplies Schematic
Mechanical Replaceable
Parts List
Exploded View
Accessories
CHANGE INFORMATION

FG 503

Section
1-FG 503
OPERATING
INSTRUCTIONS
INTRODUCTION
The
variety of swept and modulated signals available
from the FG 503 make
it especially useful for such
applications as
testing servo-system or amplifier
response,
distortion and stability . It is also useful
for FM
POWER
MODULE
Barrier
7
J +
generation or as a variable beat-frequency
oscillator . The
square wave
trigger output can be used as a source for
The FG
503 Function Generator is designed to operate

TTL logic, or to synchronize an external device such asan
in a TM 500 series power module .
Low distortion sine,

oscilloscope or counter
.
square and
triangle waveforms from 1 Hz to 3 MHz, are
available at the front panel . A +2 .5 V square wave trigger
also is available at the front panel
. Variable do offset of

INITIAL
OPERATION
±5 V is provided .
INSTRUMENT DESCRIPTION
A custom timing switch position
is provided . This
allows
the user
to
install a timing capacitor for custom
tailoring the frequency range of the FG 503 .
A voltage-controlled frequency
(VCF) input controls
the output frequencyfrom an external voltage source . The
output frequency can be swept above or below the
selected frequency, to a maximum
of 1000 :1, depending
on
the polarity and amplitude of the VCF input and the
selected output frequency .
REV . B, MAR . 1976
Top
Groove
Bottom
Groove
Fig . 1-1 . FG 503 InstaIlatlon and
removal .
CAUTION
Turn the Power Module off before inserting the
plug-
in ; otherwise, damage may occur to the plug-in
circuitry .
The FG
503 is calibrated and ready for use when
received . It is designed to operate in any compartment of
the TM 500 series power module . Refer to the power
module instruction manual for line voltage
requirements
andpower module
operation . See Fig . 1-1 for installation-
removal procedure . Check that the FG 503 is fu Ily inserted
in the powermodule . Pull the PWR switch on the power
module . Check
that the green POWER light on the FG 503
is on . The Controls, Connectors and Adjustments foldout
Slot
FG 503
PLUG-IN

Operating
Instructions-FG 503
page in Section 3 gives
acompletedescription of the front

A slot between pins 23 and 24 on the rear connector
panel controls and connectors .

identifies the
FG
503 as amember of the signal source
family . A barrier may be inserted in the corresponding
position of the power module jack, to prevent other than
signal source plug-ins from being used in that compart-
FUNCTIONS AVAILABLE AT REAR CONNECTOR

ment . This protects the plug-in should specialized con-
nections be made to that compartment . Consult the
Refer to the rear connector assignment
illustration in

Building A System section of the power modulemanual
the Service Section of this manual for pin assignments .

for further information .
RISETIME AND FALLTIME
OPERATING
CONSIDERATIONS
OUTPUT CONNECTIONS

introduced will not exceed
1%
.
This error can genera~iy be
ignored . When the rise or falltime of the test device is less
The output of the FG 503 is designed to operate as a

than ten times as'long as the combined risetimes of the
50 S2 voltage source working
into a50 S2 load . At higher

testing system, the actual risetime of the device must be
frequencies, an unterminated or improperly terminated

determined .
This
is
found from the risetime of each
output will cause excessive
aberrations
on
the output

component making up the system . The total risetime
waveform (see Impedance
Matching discussion) . Loads

equals the square
root of the sum of the squares of the
less
than 50 f2 will reduce the waveform amplitude .

individual
risetimes . R,= ~/ (R,) + (Rz) + . . .Conversely,
the risetime of the device under test can be found, from the
same
relationship, if the actual risetimes in the system are
Excessive distortion or aberrations, due to improper

known .
termination, are less likely to occur at the lower frequen-
cies (especially with sine and
triangle waveforms) . To
ensure
waveform purity, observe the following
precautions :
1 . Use good quality 50 S2 coaxial cables and connec-
tors .
2 .

Make all connections
tight and as shortas possible .
The physical and
electrical characteristics of the pulse
transmitting cable determine the characteristic im-
pedance, velocity of propagation, and amount of signal
loss . Signal loss, is related to the frequency ;
therefore, a
few feet of cable can attenuate high frequency
information
in a fast-rise pulse .
It
is
important therefore, to keep these
cables as short as
practical .
3 . Use good quality attenuators,
if it
is
necessary to

When
signal comparison measurements or time
reduce waveform amplitude to sensitive circuits .

difference determinations are made, the two signals from
the test device should travel
through coaxial cables with
identical loss and time delay characteristics .
4 . Use terminators or impedance-matching devices to
avoid reflections when
using long cables (six feet or
more)
.

If there is a do voltage across the output load, theoutput
pulse amplitude
will
be
compressed, or in some cases (if
the voltage exceeds ±10 V), it may short the
output . To
5 . Ensure that attenuators,
terminations, etc . have

prevent
this from occurring, the output must be coupled
adequate power handling capabilities
for the output

through a
do blocking capacitor to the load . The time
waveform .

constant of the coupling capacitor and load
must
be
long
enough to maintain pulse flatness .
IMPEDANCE MATCHING
If the output pulse from the FG 503 is used to measure
the rise or falltime of a device, consider the
risetime

As a pulse travels down a transmission
line, each time it
characteristics of the associated
equipment used . If the

encounters a
mismatch, or different impedance than that
risetime of
the device under test is at least ten times

of
the transmission line, a reflection is generated and sent
greaterthanthecombinedrisetimesoftheFG 503plusthe

back along the line to the source . The amplitude and
monitoring oscilloscope and associated
cables, the error

polarity of the reflections are determined by
the amount of

the encountered impedance in relation to the
characteristic impedance of the cable
.
If the mismatch
impedance is higherthan the line, the reflection will be of
the
same polarity as the applied signal .
If
it is lower, the
reflection will be of opposite polarity .
If the reflected signal returns before the pulse is ended,
it
adds to or subtracts from the amplitude of the pulse . This
distorts the pulse shape
and amplitude .
If the
FG
503
is
driving a high impedance such as the 1 MS2 input im-
pedance (paralleled
by
a stated capacitance) of the
vertical input to anoscilloscope,connectthetransmission
line to
a 50 S2 attenuator, 50 S2 termination, and then the
oscilloscope input . The
attenuator isolates the input
capacitance of the device, and the FG 503 is properly
term i nated .
A simple resistive impedance-matching network, that
provides minimum attenuation, is illustrated in Fig . 1-2 . To
matchimpedance with the illustrated network, the follow-
ing
conditions must exist :
Therefore :
or
(R, +
Zz) Rz
must equal Z,
R~+Zz~
- Rz
R, +

Z`Rz

must
equal Z z .
Z~ +
Rz
Rz = Z~
V
For example, to match a 50 S2 system to a 125 S2 system,
Z, equals 50 S2 and Zz equals 125 f2
.
Therefore :
and
z~
(Low)
Operating Instructions-FG
503
R . =

125(125 - 50) = 96 .8 ohms
125
R z =

50

=

64 .6 ohms .
125-50
m
z~
< zZ
Zz
(High)
Fig . 1-2 . Impedance matching network that provides minimum
attenuation .
When constructing such a device, the environment
surrounding
the components should be designed to
provide a transition between the impedances . The
characteristic impedance of a coaxial device is deter-
minedby the ratio between the outside diameter of the
inner
conductor to the inside diameter of the outer
conductor,
138
D
Zo = ~ IOg~o
RiRz = Z~Zz ; and R,Z~ = Rz(Zz - Zi)

f

d
D is the inside diameter of the outer conductor, d is the
diameter of the inner conductor, and F is the dielectric
constant
(1 in
air) .
R~ =

Zz(Zz -
Zi)
The network shown in Fig . 1-2 provides minimum
attenuation for a purely resistive impedance-matching
device . The attenuation as seen from oneenddoes not
equal that seen from the other end . A signal (E,) applied
and

from the lower impedance source encounters a voltage
attenuation (A,) that is greater than 1
and less than 2, as
follows :
Ez
Zz

Operating Instructions-FG 503
A signal
(Ez)
applied from the higher impedancesource

and
(Zz)
encounters a greater voltage attenuation (Az)
that is
greater than 1 and
less than 2(Zz/Z,) :
Ez R1 R1
Az = - = - + -
+1 .
E,
Rz
Z,
In the
example
of
matching 50 S2 to 125 f2,
96 .8

The illustrated network can be modified, to provide
A,

_

+ 1 = 1 .77

different attenuation ratios, by adding another resistor
125

(less than R,) between Z, and the junction of R, and
Rz .
FREE-RUNNING OUTPUT

MULTIPLIER setting, by applying a0 V to 10 V signal to
the VCF IN connector . It may be necessary to
vary the CAL
control to obtain the full 1000 :1
swept range or the lowest
swept frequency
desired . See Fig . 1-4 for maximum VCF
range for each
MULTIPLIER setting .
Set the AMPLITUDE
control fully clockwise . Notice the
two identical sets of waveforms near the
FUNCTION
selector on the
front panel . The three waveforms in the
lightly shaded area allow use of the OFFSET control
;
the
other three do not . Select the desired waveform
with or
without offset . See
Fig . 1-3
.
Select the desired frequency
with the MULTIPLIER and FREQUENCY
Hz dials . The
output frequency is calibrated when the FREQUENCY
VERNIER control is
in the full clockwise position . Connect
the load to the OUTPUT connector
and adjust the
AMPLITUDE
control for the desired output amplitude .
Fig . 1-3 . Output waveforms
available from the FG 503 .
VOLTAGE-CONTROLLED
FREQUENCY (VCF)
OUTPUT
BASIC OPERATION
96 .8 96 .8
Az =

+

+ 1 = 4 .43 .
64 .6 50
10 3
~

3 kH z

3 MHz
300 Hz

300 kHz
Z
10
30 Hz

30
kHz
W
10'
N
W

3 Hz

3 kHz
2 10 z
¢

1 Hz

300
Hz
Q
10'
W
a
1

1 H
z

30 Hz
' 0 .01
Hz *~ 5 M Hz
C
10_
z
10 - ' 1 10'
10 z 10' 10' 10 3 10 6 10'
When using the offset feature
select the waveform

(

FREQUENCY
Hz
desired in the light shaded
area . Now adjust the OFFSET
control to position
the do level (baseline) of the
output

'C
ust o mized sweep
at least 1000 :1 within this range
waveform above or below
0 V as desired .

Fig . 1-4 . Graph showing
range of frequencies for each MUL-
TIPLIER setting that canbe swept
with a0 to 10 V signal applied to
the
VCF input .
The polarity of
the VCF input signal determines
the
The output frequency of the FG 503
can be swept over a

direction the output frequency
is swept from thefrequen-
frequency

range

of

1000 :1,

depending

on

the

cy set by the MULTIPLIER, FREQUENCY
Hz, and VER-
REV . B, JULY, 197 6

Operating Instructions-FG 503
w
m
NIER controls .
A positive-going voltage raises
the fre-

range of 20 Hz to 20 kHz is desired
. Fig . 1-4showsthat no
quency, while a negative-going voltage
lowers the fre-

fixed multiplier
setting includes the desired
limits . The

n
quency . A voltage that varies
symmetrically about 0 V

value of the capacitor that must be
installed is determined

m
sweeps the output
frequency symmetrically about
the

by the
following formula :

r
center
frequency determined by the
frequency controls .

300
See Fig . 1-5 .

_
Ccus

a
Fmax

O
Z
Since the VCF input
amplitude versus frequency is a
linear relationship,
the frequency output range
may be
determined
from the VCF input amplitude .
Use a fixed do
voltage and frequency counter or other
comparison
method, to accurately determ
ine theoutput frequency and
VCF voltage
relationship . Refer to the test
under the
heading
Response Analysis for a typical
application using
the VCF feature .
CUSTOM
TIMING CAPACITOR
SELECTION

The capacitor selected
must be a low leakage non-
polarized type
within the range of 100 pF to 100
~F and
This feature
allows the user to custom select
a swept

must
have at least a 10 V rating .
Ceramic and mylar
frequency range . For
example, assume a swept frequency

capacitors work well
in this application .
VCF IN
OUTPUT
0
VCF IN
SWEPT FREQUENCY
RANGE
where C~  s is
in ~F, and
Fmax,
in Hz, is the maximum
frequency
required . Apply the formula to the example ;
v
( '
rcus
-5
V
+5
VCF IN

0
-5
OUTPUT
300
20x10'
Fig . 1-5 . Swept frequencyrange
with 10 V signals applied to
VCF IN Connector .
=

0.015
NF .
+5V
C~
w

Operating Instructions-FG 503
Remove the left side cover of the FG
503
.
Refer
to

TYPICAL VCF APPLICATION
Fig . 1-6 for capacitor location . Solder thecapacitor to the
test points located on the left rear side of the circuit board
as shown in Fig . 1-(i . Finally, set the MULTIPLIER control

The

FG 503 is particularly suited for determining
to the C position, and apply the correct voltage to the VCF

response characteristics of circuits
or systems . This
IN connector . Set the
FREQUENCY Hz
and
FREQ
VER-

application utilizes the VCF input of the FG 503 to sweep
NIER dials for the desired swept frequency range .

the
generator over
a
range of frequencies . By applying the
desired waveform from the FG 503 to a device under test,
The calibration marks on
the
FREQUENCY Hz dial are

and sweeping
the
waveform frequency over a selected
not
appropriate for use directly in determining frequency

range, various response characteristics can be observed
in the custom range position
.
It
is
possible however, to

on
a monitoring oscilloscope .
custom calibrate the dial, since the linearity of the
FREQUENCY Hz dial calbration is not changed in the
custom position .
Fig . 1-6 . Custom
timing capacitor location .
Fig . 1-7 . Phase relationships between various OUTPUT
waveforms and the TRIG OUT waveform .
TRIG OUT
Waveform
Squarewave
Triangle
Waveform
Sinewave
The following procedure describes a technique for
determining response characteristics of any frequency
sensitive device that operates within the frequency range
of
the FG 503 . Refer to the Voltage-Controlled Frequency
(VCF) Output discussion for additional information .
1 . Connect the equipment
as shown in
Fig . 1-8 .
2 . Set the MULTIPLIER selector and
FREQUENCY Hz
dial for the desired upper or lower frequency limit
(depending on the direction you may wish to sweep) . See
Fig . 1-4 for VCF ranges and MULTIPLIER
settings .
3 . Apply the desired waveform to the VCF IN connec-
tor .
4
.
Adjust the amplitude of the VCF input waveform for
the desired output frequency range .
5 .
Observe the
response
characteristics
on
the
monitoring
oscilloscope .
The frequency at which a displayed response
characteristic occurs can be determined by first removing
the VCF input waveform,
then
manually adjusting
the
FREQUENCY Hz dial to again obtain the particular
characteristic observed in the
swept
display . Then read
the frequency on the FREQUENCY Hz dial .
REV . C, MAY, 197 7