Tektronix FG501A Technical Manual
TM 9-6625-474-14&P-2
TECHNICAL MANUAL
OPERATOR, ORGANIZATIONAL,
DIRECT SUPPORT, AND GENERAL SUPPORT
MAINTENANCE MANUAL
(INCLUDING REPAIR PARTS)
FOR
FUNCTION GENERATOR
TEKTRONIX, MODEL FG 501A
(6625-01-106-9873)
DEPARTMENT OF THE ARMY
27
DECEMBER 1984
TM 9-6625-474-14&P-2
WARNING
RA PD 404264
DANGEROUS VOLTAGE
is used in the operation of this equipment
DEATH ON CONTACT
may result if personnel fail to observe safety precautions
Never work on electronic equipment unless there is another person nearby who is familiar with the
operation and hazards of the equipment and who is competent in administering first aid. When the
technician is aided by operators, he must warn them about dangerous areas.
Whenever possible, the power supply to the equipment must be shut off before beginning work on the
equipment. Take particular care to ground every capacitor likely to hold a dangerous potential. When
working inside the equipment, after the power has been turned off, always ground every part before
touching it.
Be careful not to contact high-voltage connections when installing or operating this equipment.
Whenever the nature of the operation permits, keep one hand away from the equipment to reduce the
hazard of current flowing through vital organs of the body.
WARNING
Do not be misled by the term “low voltage.”
conditions.
COMMON and probe ground straps are electrically connected. Herefore, an elevated reference applied to
any is present on each - as indicated by the yellow warning bands under the probe retractable hook tips.
For Artificial Respiration, refer to FM 21-11,
Potentials as low as 50 volts may cause death under adverse
Power Source
This product is intended to operate in a power module connected to 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.
a/(b blank)
TECHNICAL MANUAL
No. 9-6625-474-14&P-2
You can help improve this manual. If you find any mistakes or if you know of a way
to improve the procedures, please let us know. Mail your letter or DA Form 2028
(Recommended Changes to Publications and Blank Forms), direct to: Command-
er, US Army Missile Command, ATTN: DRSMI-SNPM, Redstone Arsenal, AL
35898-5238. A reply will be furnished to you.
TM 9-6625-474-14&P-2
Copyright 1980 Tektronix, Inc. All rights reserved
Reproduced by permission of copyright owner.
HEADQUARTERS
DEPARTMENT OF THE ARMY
Washington, D.C., 27 December 1984
OPERATOR, ORGANIZATIONAL, DIRECT SUPPORT,
AND GENERAL SUPPORT MAINTENANCE MANUAL
(INCLUDING REPAIR PARTS)
FOR
FUNCTION GENERATOR
TEKTRONIX, MODEL FG 501A
(6625-01-106-9873)
REPORTING OF ERRORS
LIST OF ILLUSTRATIONS
LIST OF TABLES
SECTION 0.
SECTION 1.
SECTION 2.
SECTION 3.
SECTION 4.
SECTION 5.
TABLE OF CONTENTS
Page
iii
iv
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1-1
2-1
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2-2
2-4
2-5
2-6
2-9
3-1
4-1
4-1
4-8
5-1
5-1
5-4
This manual is, in part, authenticated manufacturer’s commercial literature. Recommended Spare Parts List has been added to supplement the commercial
literature, The format of this manual has not been structured to consider levels of maintenance.
i
TM 9-6625-474-14&P-2
SECTION 6.
SECTION 7.
SECTION 8.
SECTION 9.
APPENDIX A.
APPENDIX B.
APPENDIX C.
APPENDIX D.
OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
REPLACEABLE ELECTRICAL PARTS, . . . . . . . . . . . . . . .
DIAGRAMS AND CIRCUIT BOARD ILLUSTRATIONS . . . . . . .
REPLACEABLE MECHANICAL PARTS . . . . . . . . . . .
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MAINTENANCE ALLOCATION CHART (MAC) . . . . . .
RECOMMENDED SPARE PARTS LIST..... . . . . . . . . . . . . . . . . . . .
MANUAL CHANGE INFORMATION. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .
TABLE OF CONTENTS (CONT)
Page
6-1
7-1
8-1
9-1
A-1
B-1
C-1
D-1
ii
LIST OF ILLUSTRATIONS
TM 9-6625-474-14&P-2
Fig. No.
0-1
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-11
2-12
4-1
4-2
4-3
4-4
4-5
5-1
5-2
5-3
5-4
Title
FG 501A 2 MHz Function Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installation and Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Controls and Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Swept Frequency Range (VCF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Basic Functions (Waveforms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ramps and Pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phase Relationships (Output and Trig) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trigger Signal Amplitude Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gated Operation (Waveforms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Triggered Operation (Waveforms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phase Control (Waveforms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analyzing Circuit or System Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tone Burst Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Setup for Dial Alignment and Offset Adjustment . . . . . . . . . . . . . . . . . . . . .
Test Setup for Sine Distortion Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Setup for Offset and Sine/SquareAmplitude
Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Setup for Squarewave Comp/Rise and Falltime
Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Setup for Dial Cal and Loop Delay Adjustment . . . . . . . . . . . . . . . . . . . . . . .
Coaxial End Lead Connector Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Orientation and Disassembly of Multipin Connectors . . . . . . . . . . . . . . . . . . . . . .
Extension Shaft and Pushbutton Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rear Interface Connector Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0-2
2-1
2-3
2-6
2-7
2-7
2-7
2-7
2-8
2-8
2-8
2-9
2-10
4-9
4-11
4-12
4-13
4-14
5-3
5-3
5-4
5-5
iii
TM 9-6625-474-14&P-2
LIST OF TABLES
Table No.
1-1
1-2
1-3
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Title Page
1-4 Physical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4-1
5-1
Test Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Relative Susceptibility to Static Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-4
1-4
1-5
4-1
5-1
iv
SECTION 0
GENERAL INFORMATION
TM 9-6625-474-14&P-2
0-1. Scope. This manual contains instructions for
the operator, organizational, direct support, and general support maintenance of and calibration procedures for Tektronix Function Generator, Model FG
501A. Throughout this manual, Tektronix Function
Generator, Model FG 501A is referred to as the FG
501A.
0-2. Indexes of publications. a. DA Pam 310-4.
Refer to the latest issue of DA Pam 310-4 to determine whether there are new editions, changes, or
additional publications pertaining to Tektronix Function Generator, Model FG 501A.
b. DA Pam 310-7. Refer to the latest issue of DA
Pam 310-7 to determine whether there are modification work orders (MWO’S) pertaining to Tektronix
Function Generator, Model FG 501A.
0-3. Forms, Records, and Reports. Department of
Army forms and procedures used for equipment maintenance and calibration are those prescribed by TM
38-750, The Army Maintenance Management System.
Accidents involving injury to personnel or damage to
materiel will be reported on DA Form 285,
Report, in accordance with AR 385-40.
Accident
0-4. Reporting Equipment Improvement Recommendations (EIR). If your FG 501A needs im-
provement, let us know. Send us an EIR. You, the
user, are the only one who can tell us what you don’t
like about your equipment. Let us know why you don’t
like the design. Tell us why a procedure is hard to
perform. Put it on an SF 368 (Quality Deficiency
Report). Mail it to Commander, U.S. Army Missile
Command, ATTN: DRSM1-CIMD, Redstone Arsenal,
AL 35898-5290. We’ll send you a reply.
0-5. Administrative Storage. To prepare the Tektronix Function Generator, Model FG 501A for placement into and removal from administrative storage,
refer to Section 3, Chapter 4, AR 750-25-1, Maintenance of Equipment and Supplies. Temporary storage
should be accomplished in accordance with TB 75025-1, Section 2, Maintenance of Supplies and
Equipment.
0-6.
Materiel. Destruction of Tektronix Function
Generator, Model FG 501A to prevent enemy use shall
be in accordance with TM 750-244-2.
Destruction
of Army Electronics
0-1
TM 9-6625-474-14&P-2
.
0-2
FIG.0-1. FG 501A 2MHz FUNCTION GENERATOR
SECTION 1
SPECIFICATION
TM 9-6625-474-14&P-2
INTRODUCTION
This section of the manual contains a general description of the FG 501A and complete electrical, environmental, and physical specifications. Standard accessories are
also listed. Instrument option information is located in the
back of this manual in a separate section.
INSTRUMENT DESCRIPTION
The FG 501A Function Generator provides low distortion sine, square, triangle, ramp, and pulse waveforms
over the frequency range 0.002 Hz to 2 MHz in eight
decade steps. Dc offset up to ±13 V is available. Waveform
triggering and gating functions, in addition to being slope
(+ or –) selectable, are provided with variable phase
control capable of up to ±90° phase shift. The symmetry
of the output waveform may also be varied from 5 to 95%.
Step attenuators provide up to 60 dB of attenuation in
20 dB steps. A variable amplitude control provides an
additional 20 dB attenuation.
A voltage-controlled frequency (VCF) input is provided
to control the output frequency from an external voltage
source. The output frequency can be swept above and
below the selected frequency to a maximum of 1000:1
depending on the polarity and amplitude of the VCF input
signal and the selected output frequency.
ACCESSORIES
The only accessory shipped with the FG 501A is the
Instruction Manual.
PERFORMANCE CONDITIONS
The electrical characteristics are valid with the follow-
ing conditions:
1. The instrument must have been adjusted at an
ambient temperature between +20° C and +30° C and
operating at an ambient temperature between 0° C and
+50° C.
The instrument must be in a non-condensing en-
2.
vironment whose limits are described under Environmen-
tal.
3. Allow twenty minutes warm-up time for operation to
specified accuracy; sixty minutes after exposure to or
storage in high humidity (condensing) environment.
Items listed in the Performance Requirements column
of the Electrical Characteristics are verified by completing
the Performance Check in this manual. Items listed in the
Supplemental Information column may not be verified in
this manual; they are either explanatory notes or performance characteristics for which no limits are specified.
1-1
TM 9-6625-474-14&P-2
Table 1-1
ELECTRICAL CHARACTERISTICS
Characteristics
Frequency
Range
Sine-wave, square-wave,
and triangle
Ramp and Pulse
Variable Symmetry
Duty Cycle
Output Amplitude
Output Impedance
Performance Requirements
.002 Hz to 2 MHz
.002 Hz to 200 kHz ± 10% calibrated
portion of dial.
At least
30 V P-P into an open
circuit, at least 15 V p-p into
50
Cl,
(Front panel only.)
Supplemental Information
Provided in eight decade steps plus
variable, with overlap on all
ranges.
Calibrated portion of dial extends
from 20 to 2. Portion of dial from
2 to .2 is uncalibrated
.0002 Hz to .002 Hz uncalibrated
portion of dial.
Measured at 50% duty cycle.
.0002 Hz to .002 Hz uncalibrated
portion of dial.
Activation of Symmetry control
divides output frequency by
=10.
Offset control off.
Front panel z
= 50 (2 ±10%
o
ATTEN in 0 dB position.
Offset Range
Frequency Resolution
Stability (Frequency)
Time
Temperature
At least ±13 V into open circuit,
at least ±6.5 V into 50
Q.
Maximum peak signal plus offset
cannot exceed ±15 V into an
open circuit, or ±7.5 into 50
Q.
(Front panel only,) Offset reduced
by attenuators.
Rear interface z
1 part in 10
= 600 Cl –10%.
O
4
of full scale with
frequency vernier control.
Within 2% from .2 Hz to 2 MHz, and
within 10% from .002 Hz to .2 Hz. The
FREQUENCY Hz dial must be on the
calibrated portion. The instrument
must be in a temperature between
0° C and +50° C and checked
after a 1 hour warmup. VAR SYMM
control disabled,
1-2
Table 1-1 (cont)
TM 9-6625-474-14&P-2
Characteristics
Amplitude Flatness
Sinewave
(10 kHz Sinewave Ref)
Squarewave
(10 kHz Squarewave Ref)
Triangle
(10 kHz Triangle Ref)
Sinewave Distortion
Performance Requirements
Measured with 0 dB ATTEN button
“IN” and output driving 50
(Front panel only.)
±0.1 dB 20 Hz to 20 kHz
±0.5 dB 20 kHz to 1 MHz
±1 dB 1 MHz to 2 MHz
Peak to peak amplitude within
±0.5 dB of squarewave reference
amplitude 20 Hz to 2 MHz.
Peak to peak amplitude within
±0.5 dB of triangle wave reference amplitude 20 Hz to 200 kHz.
Within 2 dB 200 kHz to 2 MHz.
range and below.
Cl
load.
Supplemental Information
Typically ±.5 dB .002 Hz to 20 Hz
Typically within ±.5 dB .002 Hz
to 20 Hz.
Typically within ±.5 dB .002 Hz
to 20 Hz.
20° to 30° C. Measured with
with average responding THD meter.
Measurement bandwidth limited to
approximately 300 kHz.
Q
Verified at 15 V p-p into 50
Must be on calibrated portion of
dial. VAR SYMM control off, Offset
control off.
load.
Squarewave Output
Risetime and Falltime
Aberrations (p-p)
Pulse Output
Risetime and Falltime
Aberrations (p-p)
VCF Input
Ext Trig/Gate Input
Impedance
Threshold Level
Trigger Output
Variable Phase Range
All harmonics at least 30 dB below
fundamental from 100 kHz to 2 MHz
Step ATTEN in 0 dB position.
<25 ns at 15 V p-p into 50
s30/o (Front panel only. )
Step ATTEN in 0 dB position.
<25 ns at 15 V p-p into 50
<30/o (Front panel only.)
+1
V ±20%.
>
+4 V into open circuit
>+2Vinto50f2.
At Ieast ±90°
Q
Q,
Trig output driving open circuit.
Positive going voltage increases
frequency. Maximum Slew Rate =
0.5
V/Ps.
VCF must not exceed
range limits, Maximum input
=2
kf2
Maximum input
Sine and Triangle only.
<15
V pk.
<15 V pk.
1-3
TM 9-6625-474-14&P-2
Table 1-1 (cont)
Characteristics
Attenuators
Accuracy
Dial Accuracy
Triangle
Linearity
Time Symmetry
Characteristics
Power Consumption
Performance Requirements
±1 dB.
Within 3% of full scale 20 to 2.
Better than 1% 20 Hz to 200 kHz.
5% 200 kHz to 2 MHz (calibrated).
Table 1-2
MISCELLANEOUS
12 W or less. (plug-in only)
Supplemental Information
60 dB in 20 dB steps. >20 dB
additional attenuation with amplitude
control.
Verified at 20 kHz.
2 to .2 Uncal.
Greater than or equal to 99% 20 Hz to
200 kHz. 97% 200 kHz to 2 MHz (calibrated). Measured from 10% to
90% of waveform.
Description
Recommended Adjustment
Interval
Warm-up Time
Characteristics
Temperature
Operating
Non-operating
Humidity
Altitude
Operating
Non-operating
Vibration
1000 hours or 6 months, whichever occurs first.
20 minutes.
Table 1-3
ENVIRONMENTAL’
Description
Meets MlL-T-28800B, class 5.
0° C to +50° C
–55° C to +75° C
95% RH, 0° C to 30° C
Exceeds MlL-T-28800B, class 5.
75% RH to 40° C
45% RH to 50° C
Exceeds MIL-T-28800B, class 5.
4.6 Km (15,000 ft)
15 Km (50,000 ft)
0.38 mm (0.015") peak to peak,
5 Hz to 55 Hz, 75 minutes.
Exceeds MlL-T-28800B, class 5,
when installed in qualified
power modules.
b
1-4
Table 1-3 (cont)
TM 9-6625-474-14&P-2
Characteristics
Shock
Bench Handling
Transportation
C
c
EMC
Electrical Discharge
a
With power module.
b
Refer to TM 500 power module specifications.
c
Without power module.
Description
30 G’s (1/2 sine), 11 ms duration, 3 shocks in each direction along 3 major axes, 18
Meets MlL-T-28800B, class 5,
when installed in qualified
power modules.
b
total shocks.
12 drops from 45°, 4“ or
Meets MlL-T-28800B, class 5.
equilibrium, whichever occurs
first.
Qualified under National Safe Transit Association Preshipment Test
Procedures 1A-B-1, and 1A-B-2.
Within limits of MIL-461A, and F.C.C. Regulations, Part 15, Subpart J,
Class A.
20 kV maximum charge applied to instrument case.
Table 1-4
Characteristics
Finish
Net Weight
Overall Dimensions
PHYSICAL CHARACTERISTICS
Description
Plastic/aluminum laminate front panel. Anodized aluminum chassis.
1.88 Ibs (.85 kg)
Height 5 in (126mm)
Width 2.6 in (67mm)
Length 11.9 in (303mm)
1-5/(1-6 blank)
TM 9-6625-474-14&P-2
SECTION 2
OPERATING INSTRUCTIONS
INTRODUCTION
This section of the manual provides operating information required to obtain the most effective performance
from the FG 501A. Included are installation and removal
instructions, a functional description of the front panel
controls, and a general description of the operating
modes. Some basic applications of the instrument are also
briefly discussed.
INSTALLATION AND REMOVAL
The FG 501A is calibrated and ready to use when
received. It operates in one compartment of any TM 500series power module. Refer to the power module instruc-
tion manual for line voltage requirements and power
module operation.
CAUTION
To prevent damage to the FG 501A, turn the power
module off before installation or removal of the
instrument from the mainframe. Do not use excessive force to install or remove.
showing: owner (with address) and the name of an
individual at your firm that can be contacted. Include
complete instrument serial number and a description of
the service required.
If the original package is not fit for use or not available,
repackage the instrument as follows:
Surround the instrument with polyethylene sheeting, or
other suitable material, to protect the exterior finish.
Obtain a carton of corrugated cardboard of adequate
strength and having inside dimensions no less than six
inches more than the instrument dimensions. Cushion
the instrument by tightly packing dunnage or urethane
foam between the carton and the instrument, on all
sides. Seal the carton with shipping tape or an industrial stapler.
The carton test strength for your instrument is 200
pounds.
Check to see that the plastic barriers on the interconnecting jack of the selected power module compartment match the cutouts in the FG 501 A circuit board edge
connector. If they do not match, do not insert the
instrument until the reason is found. When the units are
properly matched, align the FG 501A chassis with the
upper and lower guides of the selected compartment (see
Fig. 2-1). Insert the FG 501A into the compartment and
press firmly to seat the circuit board edge connector in the
power module interconnecting jack. Apply power to the
FG 501A by operating the power switch on the power
module.
To remove the FG 501A from the power module, pull
the release latch (located in the lower left corner) until the
interconnecting jack disengages. The FG 501A will now
slide straight out.
REPACKAGING FOR SHIPMENT
If the Tektronix instrument is to be shipped to a
Tektronix Service Center for service or repair, attach a tag
Fig. 2-1. Plug-in installation and removal.
2-1
TM 9-6625-474-14&P-2
CONTROLS AND CONNECTORS
Although the FG 501A is calibrated and ready to use,
the functions and actions of the controls and connectors
should be reviewed before attempting to use it. All
controls necessary for operation of the instrument are
located on the front panel. A brief description of these
controls follows. Refer to Fig. 2-2.
2-2
Fig. 2-2. Controls and connectors.
TM 9-6625-474-14&P-2
POWER - llluminated when power is applied to the
FG 501A.
FREQUENCY CONTROL AND FUNCTION
SELECTION
FREQUENCY Hz - Selects the frequency of the
output waveform
MULTIPLIER control.
FREQ + 10 - Illuminated when the variable symmetry function is activated.
FUNCTION BUTTONS - Select square, triangle,
and sine waveforms.
VAR SYMM - (push to enable) adjusts time-based
symmetry of the selected output waveform. Reduces
the frequency of the output waveform by a factor
= 10 and illuminates the FREQ + 10 indicator.
FREQUENCY VERNIER - For fine adjustment of
output frequency to at least 1 part in 10
MULTIPLIER - Selects the output frequency in eight
decade steps in conjunction with the FREQUENCY
Hz control.
in
conjunction with the
4
of full scale.
TRIGGER AND GATE CONTROLS
GATE - When pressed causes continuous output of
the selected waveform for the duration of the gating
pulse.
SLOPE - Button selects, in TRIG mode, the slope of
the input signal which will trigger the selected
output waveform. In GATE mode, whether output
gating will occur when the level of the input signal is
above or below the threshold level of +1 V.
TRIG/GATE lN - Bnc connector used to apply the
external trigger or gating signal.
VCF lNPUT - Bnc connector for applying an exter-
nal voltage for controlling the output frequency of
the generator.
TRIGGER OUTPUT - Bnc connector which outputs
one positive pulse for each cycle of the selected
output waveform.
OUTPUT CONTROLS
ATTENUATOR BUTTONS - Attenuate the ampli-
tude of the selected output waveform in 20 dB steps
to a maximum of 60 dB when pressed.
AMPL - Varies the amplitude of the selected output
waveform, between steps of the attenuator buttons.
VAR
0
relative to input trigger or gate waveform.
FREE RUN - When pressed causes continuous
waveform output.
TRIG - When pressed causes output of one cycle of
selected waveform for each trigger pulse applied to
the TRIG/GATE IN connector.
- Selects phase lead or lag, up to ±90°,
OFFSET - Pull and turn control, concentric with the
AMPL control, provides up to ±13 V dc offset of the
output waveform.
OUTPUT - Bnc connector for output of the selected
waveform.
RELEASE LATCH - Pull to disengage the FG 501A
from the power module.
2-3
TM 9-6625-474-14&P-2
OPERATING CONSIDERATIONS
OUTPUT CONNECTIONS
The output of the FG 501A is designed to operate as a
50
fl
voltage source working into a 50 Q load. At higher
frequencies, an unterminated or improperly terminated
output will cause aberrations on the output waveform.
Loads less than 50
Excessive distortion or aberrations, due to improper
termination, are less noticeable at the lower frequencies
(especially with sine and square waveforms). To ensure
waveform purity, observe the following precautions:
1. Use good quality 50
tors.
2. Make all connections tight and as short as possible.
3. Use good quality attenuators if it is necessary to
reduce waveform amplitude applied to sensitive circuits.
4. Use terminations orimpedance matching devices to
avoid reflections when using long cables (6 feet or more).
~
will reduce the waveform amplitude.
Q
coaxial cables and connec-
capacitance) of the vertical input of an oscilloscope,
Q
connect the transmission line to a 50
termination, and then to the oscilloscope input. The
attenuator isolates the input capacitance of the device,
and the FG 501A is properly terminated.
attenuator, 50
FIRST TIME OPERATION
The Controls and Connectors pages give a description
of the front panel controls and connectors, The waveform
selection and frequency determining control sareoutlined
in blue, the trigger function controls and inputs are
outlined in green, and the output controls are outlined in
black.
The following exercise will familiarize the operator with
most functions of the FG 501A.
NOTE
If any discrepancies are encountered during the
exercise, refer the condition to qualified service
personnel,
Q
5. Ensure that attenuators, terminations, etc. have
adequate power handling capabilities for the output
waveform.
If there is a dc voltage across the output load, use a
coupling capacitor in series with the load. The time
constant of the coupling capacitor and load must be long
enough to maintain pulse flatness.
RISETIME AND FALLTIME
If the FG 501A is used to measure the rise or falltime of
a device, the riestime characteristics of associated equipment should be considered. If the risetime of the device
under test is at least 10 times greater than the combined
risetimes of the FG 501A and associated equipment, the
error introduced will not exceed
ignored. When the rise or falltime of the test device is less
than 10 times as long as the combined risetimes of the
testing system, the actual risetime of the system must be
calculated. The risetime of the device under test can be
determined once the risetime of the system is known.
1%, and generally can be
IMPEDANCE MATCHING
If the FG 501A is driving a high impedance such as the
1
MQ
input impedance (paralleled by a stated
Preset the controls as follows:
Blue section:
FREQUENCY Hz
MULTIPLIER
FREQUENCY VERNIER
WAVEFORM—SINE
VAR SYMM
Green section:
FREE RUN
Black section:
ATTENUATOR
AMPL (variable)
OFFSET
Connect a 50
the vertical input of an oscilloscope. Set the oscilloscope
controls to:
Vertical
Horizontal (Time Base)
The oscilloscope should display 1 complete cycle per
division of the sine waveform ( approximately 10 cycles
across the graticule),
Q
bnc coaxial cable terminated in 50 f2to
10
10
Fully CW
in
off
in
-20 dB
Centered
off
1 V/Div DC Coupled
1 ms/Div
2-4
TM 9-6625-474-14&P-2
1. Alternately press the square, triangle and sine
buttons and observe the different waveshapes. Return to
the preset condition.
2. Alternately press the four attenuator buttons and
rotate the AMPL (variable) control to verify that the
waveform amplitude changes. Return these controls to the
preset condition.
3. Pull the OFFSET knob out and rotate it. Notice the
change in dc level of the displayed waveform. Return the
OFFSET knob to the in position.
OPERATING MODES
FREE-RUNNING OUTPUT
The following procedure will provide a free-running
output with variable frequency and amplitude.
1. Select the desired waveform.
4. Push the VAR SYMM button to release it to the out
position. Observe that the FREQ
luminated and only one cycle of the output waveform is
displayed. Rotate the VAR SYMM control through its
range and notice the change in shape of the square,
triangle, and sine waveforms (with the appropriate buttons
pushed in). Return the controls to the preset condition.
5. Rotate the FREQUENCY control and the
MULTIPLIER switch while observing the change in frequency of the displayed
to the preset condition,
If more than one cycle of the output waveform is
desired, push the GATE button. The output will now be
continuous for the duration of the gating waveform. The
number of cycles per burst can be approximated by
dividing the gating signal duration by the period of
FG 501A output frequency,
waveform, Return these controls
+
10 indicator is il-
2. Set the AMPL control fully counterclockwise. Check
that the VAR SYMM and OFFSET controls are in the off
(in) position.
3. Select the desired frequency with the FREQUENCY
Hz dial and MULTIPLIER switch. Frequency equals dial
setting times multiplier setting.
4. Connect the load to the FG 501A output connector
and adjust the AMPL control for the desired output
amplitude.
TRIGGERED OR GATED (BURST)
OPERATION
With the FG 501A set for free-running operation, as
described in previous paragraphs, apply the triggering or
gating signal to the TRIG/GATE IN connector.
If only one cycle of the output waveform per trigger is
desired, push the TRIG button and select + or – slope.
One output cycle will now be generated for each input
trigger cycle.
In triggered or gated operation the PHASE control
varies the start of the output waveform by ±90°. This
phase change is measured from the 0 V, 0° point on the
output waveform.
VOLTAGE CONTROLLED FREQUENCY
(VCF) OPERATION
The output frequency of any selected waveform can be
swept within a range of 1000:1 by applying an external
voltage to the VCF INPUT connector. The polarity of the
VCF input signal determines which direction the output
frequency sweeps from the selected frequency, A positive
(+) going signal increases the frequency while a negative
(–) going signal decreases the frequency. The amplitude
and polarity of the input voltage can be selected within a
range of ±10 V depending on the FREQUENCY Hz dial
setting.
The maximum swept frequency range of 1000:1 encom-
passes the uncalibrated portion of the FREQUENCY Hz
dial (<.2 to 2). To ensure that the frequency does sweep at
least a range of 1000:1, it is recommended that the
FREQUENCY Hz dial be set at .2 and a 0 to +10 V signal be
applied to the VCF INPUT connector. It may be necessary
2-5
TM 9-6625-474-14&P-2
to vary the FREQUENCY VERNIER control to obtain the
full 1000:1 swept range or the lowest swept frequency
desired.
Since the VCF input amplitude is a linear relationship,
the frequency output range can be determined from the pulse is generated for each negative cycle of the output
VCF input amplitude.
A +4 V square wave is available from the TRIG
OUTPUT connector. The frequency of the trigger output
is determined by the frequency of the selected output
waveform. One trigger pulse is generated for each positive
cycle of the output signal except when square waves are
selected. When generating square waves, one trigger
signal. Trigger output impedance is
TRIGGER OUTPUT
50’(2.
BASIC WAVEFORM CAPABILITIES
The following photographs illustrate the basic waveform capabilities of the FG 501A.
2-6
Fig. 2-3. Swept Frequency range with 10 V signals applied to VCF IN connector.
TM 9-6625-474-14&P-2
Fig. 2-4. BASIC FUNCTIONS. Square, triangle, and sine
waveforms selected by front panel pushbuttons.
Fig. 2-6. Phase relationships between OUTPUT waveforms and
the TRIG OUT waveform.
Fig. 2-5. RAMPS AND PULSES. These are obtained from the Fig. 2-7. Trigger Signal amplitude requirements and triggering
basic waveforms by using the SYMMETRY control.
points.
2-7
TM 9-6625-474-14&P-2
Fig. 2-8. GATED OPERATION. The top three traces are various
output waveforms and the bottom trace is the gating waveform
applied to the trigger INPUT connector with the GATE
pushbutton pressed in. Note the additional cycle completed after
the waveforms are gated off.
Fig. 2-10. PHASE CONTROL OPERATION. This photograph
illustrates PHASE control usage in the triggered mode. The five
super-imposed traces illustrate the effect of the phase control.
This control provides ±90° of shift. The bottom trace is the
triggering waveform.
Fig. 2-9. TRIGGERED OPERATION. The top three traces are the
various out put traces selected. The bottom trace is the triggering
waveform applied to the trigger INPUT connector with the TRIG
mode selected. Note that only one cycle of the output waveforms
is completed.
2-8
APPLICATIONS
TM 9-6625-474-14&P-2
RESPONSE ANALYSIS
The FG 501A is particularly suited for determining
resIponse characteristics of circuits or systems. This
application utilizes the VCF input of the FG 501 Ato sweep
the generator over a range of frequencies. Refer to the
Voltage Controlled Frequency (VCF) Operation discussion under Operating Modes for additional information.
1. Connect the equipment as shown in Fig. 2-11.
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 and reading
that frequency on the FREQUENCY Hz dial.
TONE-BURST GENERATION OR
2. Set the MULTIPLIER selector and FREQUENCY Hz
dial for the desired upper or lower frequency limit
(depending on the direction you wish to sweep).
The FG 501A can be used as atone-burst generator or
frequency multiplier for checking tone-controlled
3. Apply the desired waveform to the VCF INPUT
connector. (A positive-going waveform will increase the
frequency while a negative-going waveform will decrease
it. )
4. Adjust the amplitude of the VCF input waveform for
the desired output frequency range. obtaining a tone-burst or frequency multiplied output
devices. This application utilizes a ramp generator, such
as the TEKTRONIX RG 501, as a VCF signal source and a
pulse generator, such as the TEKTRONIX PG 501, as a
gating signal source.
The following procedure describes a technique for
STEPPED FREQUENCY
MULTIPLICATION
Fig. 2-11. Analyzing circuit or system response.
2-9
TM 9-6625-474-14&P-2
from the FG 501A. Refer to the Gated (burst) Output and
Variable Phase and the Voltage-controlled Frequency
(VCF) Output discussions under Operation for additional
information.
1. Connect the equipment as shown in Fig. 2-12.
2. Push the GATE button in and set the PHASE control
to the desired phase.
3. Set the ramp generator for the desired ramp dura-
tion and polarity.
4. Adjust the pulse generator period for the desired
number of bursts within the selected ramp duration. input waveforms, i.e., triangle, sine, square, etc.
Adjust the pulse generator duration for the desired burst
width.
5. Select the sweep frequency range by adjusting the
FREQUENCY Hz dial for one end of the sweep range
(upper or lower limit depending on the polarity of the
ramp). Then, adjust the ramp generator amplitude for the
other swept frequency limit.
Various other tone-burst or frequency multiplied
characteristics can be obtained by using different gating
2-10
Fig. 2-12. Tone-burst generation or stepped frequency multiplication.
TM 9-6625-474-14&P-2
SECTION 3
THEORY OF OPERATION
INTRODUCTION
This section of the manual contains a description of the
electrical circuits in the FG 501A. Refer to the block throughout this section refer to the schematic diagram on
diagram and schematic diagrams on the fold out pages in which the circuit being discussed is located.
the back of the manual to aid in understanding this
LOOP
FREQUENCY CONTROL AND SUMMING
AMPLIFIER
The voltage developed across the frequency control
divider string, R1429, R1321, R500 and R510, is applied to
pin 5 of operational amplifier U1540B. This voltage is
buffered by the amplifier and. a current is developed
through R1551. This current is applied top in 2 of summing
amplifier U1540A where it is summed with any currents
developed by a voltage applied tothe VCF inputs. The VCF
inputs are J510 (front panel) through R1553, and pin 21B
(rear interface) through R1103. These summed currents
are buffered by Q1445 and flow through R1543. The
voltage developed across R1543 is proportional to the
frequency.
CURRENT SOURCES AND SWITCH
The voltage developed across R1543 is buffered by
U1440 and Q1541 which form the negative current source
for the main Ioop timing circuitry. This same voltage is also
buffered by U1540C and Q1543 which form a current
source identical to U1440 and Q1541. The output current
from Q1543 flows through Q1527, Q1525, and Q1421,
which form a current mirror that inverts this current to
provide the positive current source for the main loop
timing circuitry. The current through R1521 is the timing
capacitor charging current; the current through R1536 is
the discharging current. The Top Dial Symmetry Cal,
R1421, adjusts the balance between these two currents so
they are equal in magnitude.
description. Diamond enclosed numbers appearing
@
positive and negative current sources. In this manner the
symmetry of the waveform generated by the loop is varied.
These currents are switched into the junction of CR1531
and CR1533 where they alternately charge and discharge
the timing capacitor, producing a triangle waveform, The
current switch is formed by Q1531, CR1531, Q1433 and
CR1533.
TIMING CAPACITORS AND
@
@
5
(C1631)
0
down to
CAPACITANCE MULTIPLIER
The timing capacitors provide for triangle generation in
the five fastest MULTIPLIER ranges. They are switched
into and out of the circuit in decade stepsfrom 10
down to 10
For the four lower MULTIPLIER ranges, 10
10-’,
C1741 is switched into the feedback loop of U1930
forming an integrator. Current from the current switch is
applied to operational amplifier U1940. A voltage is
developed at the output of this amplifier that is propor-
tional to the applied current times the value of R1941
(1
kfl).
resistors, to the input of U1930. These resistors, R1831,
R1841, R1842, and R1843, are switched into and out of the
circuit in decade steps with the MULTIPLIER switch
S1731. This arrangement provides very large values of
effective capacitance. The output of U1930 is now the
triangle that is applied to the buffer stage.
1
(C1741).
This voltage is applied, across one of four
TRIANGLE BUFFER
In the normal mode of operation (fixed symmetry) R520
and R540 are in the emitter circuit of Q1541 and Q1543. In
this condition, equal amounts of current will flow in both
the positive and negative current sources. When S500,
VAR SYMM, is activated, R530 is switched into the current
source emitter circuits. As R530 is varied from one end to
the other, unequal amounts of current flow through the
The voltage developed by the timing capacitor or
multiplier (U1930) is applied to the triangle buffer. Q1725
and Q1723 form the differential input stage of this circuit.
Q1821 serves as a constant current source for the input
differential pair. Q1721 and Q1712 complete the feedback
for the amplifier such that the voltage at the emitter of
Q1712 is equal to the voltage at the Gate of Q1725.
3-1
TM 9-6625-474-14&P-2
Loop delay compensation is provided by a network
comprised of R1712, R1812, C1712, and C1714. The
buffered timing capacitor voltage is applied through this
network to the level comparators.
(~)
low and pin 8
to the current switch, Q1531 will be turned off and Q1433
turned on. This allows the timing capacitor to charge in the
positive direction.
to go high. Taking this high at pin 8 back
LEVEL COMPARATORS
The level comparators detect upper and lower
threshold levels. U1700A is the upper level detector and
U1700B the lower. The reference level for these comparators is supplied by U1400B and C. As the threshold
levels are detected, the respective comparator triggers
U1600B.
REFERENCE VOLTAGES
The reference voltage supplies are composed of
U1400B (–) and U1400C (+) and associated components.
The upper (positive) level threshold voltage is established
by adjusting R1412. This resistor is in a voltage divider
string from zener diode VR1413. The voltage developed
across R1412 is buffered by U1400C and set to approximately +400 mV at the output. This voltage is applied
to pin 5 of U1700A as the upper threshold level reference.
This same voltage is also applied to pin 9 of inverter
U1400B. R1511 is used to adjust the gain of this stage so
that the output is nominally –400 mV. This voltage is
applied to pin 13 of U1700B as the lower threshold level
reference.
LOOP LOGIC
When a rising voltage at pin 6 of U1700A passes
through the threshold level set at pin 5, the output (pin 8)
goes low pulling pin 10 of U1600Blow. This action sets the
flip-flop causing pin 9 (Q) to go high and pin 8 (Q) to go
low. Pin 8 of U1600B is tied back, through R1403, to the
junction of CR1431 and VR1532. VR1532 serves as a level
shifter to change the TTL output gate to the correct level to
drive the current switch (Q1531, CR1531, Q1433,
CR1533).
As the voltage at the junction of R1532 and R1534
drops, it pulls the bases of Q1531 and Q1433 low. Q1531 is
turned on and Q1433 is turned off. Any current from the
positive current source, through R1521, now flows
through Q1531 and is shunted to the –15 V supply. With
Q1433 turned off, any current flow through the negative
current source must come from the positively charged
timing capacitor through CR1533.
The falling voltage on the timing capacitor is buffered
through the triangle buffer and applied to the level
comparators U1700A and U1700B. As the voltage at pin 12
of U1700B falls through the threshold level set at pin 13,
the output (pin 1) goes low pulling pin 13 of U1600Blow.
This action resets the flip-flop causing pin 9
(Q) tonowgo
The action just described generates one entire cycle of
a triangle wave.
TRIGGER GENERATOR
The square wave output at pin 8
drives the trigger output amplifier. This circuit is composed of emitter follower Q1431 and associated components. Q1440, in conjunction with R1440, serves as
output short circuit protection. The output of this circuit
(at J2043) is a square wave 180° out of phase with the main
loop signal. The output amplitude is greater than +4 V into
an open circuit, and at least +2 V into a 50
(~)
of U1600B also
f2
load.
SQUARE WAVE GENERATOR
The output at pin 9 (Q) of U1600B is a square wave, but
180° out of phase with that at pin 8. This signal is used to
drive the square wave generator composed of differential
pair Q1801, Q1901, and associated components. The base
of Q1901 is held at a constant voltage by divider network
R1815 and R1818. R1728 and R1816 form a constant
current source for the differential pair. The square wave
from U1600B alternately switches this constant current to
ground through Q1801 or through R1819 and Q1901. In
this manner, a square wave voltage is developed with dc
levels sufficient to drive the output amplifier for the square
wave function.
PHASE CLAMP THRESHOLD DETECTOR
The output of the triangle buffer, in addition to possibly
being fed to the Output Amplifier through S1901B, is
connected to the base of Q1711. Q1711 and Q1611 form a
differential amplifier. Q1621 and associated components
provide a constant current source for the differential pair.
This amplifier senses the level of the triangle waveform
and compares it to the output voltage of U1400A. The
output voltage of U1400A is determined by the setting of
the VAR 0 control, R550. The voltage range of R550 is
established by reference voltage supplies U1400B (–) and
U1400C (+). These are the same reference voltages
supplied to the Level Comparators. This arrangement
permits comparison of the triangle voltage with the
maximum possible positive and negative levels, and all
levels between.
When the triangle voltage exceeds the reference
voltage set by the VAR 0 control, Q1711 turns off. Any
current flowing through Q1621 now flows through Q1611.
3-2
TM 9-6625-474-14&P-2
CURRENT AMPLIFIER
Current flowing through Q1611 also flows through
R1622 and is amplified by Q1521. Temperature compensation for this amplifier is provided by CR1621. Differential
pair Q1511 and Q1523 serve as a current switch. With
Q1511 turned off, any current amplified by Q1521 passes
through Q1523 to the junction of CR1531 and CR1533.
When the timing capacitor voltage rises to the threshold
TRIG/GATE AMP AND SINE SHAPER
TRIG/GATE AMP AND LOGIC
The input trigger amplifier consists of an emitter
coupled differential pair (Q1320 and Q1322), current
amplifier Q1324, and the required logic circuitry to control
the operation of the main loop phase clamp. Input circuit
protection is provided by R1203, R1204, CR1220 and
CR1221. Triggering signals are applied either through
front panel connector J520 or interface connections on
the rear edge of the Main circuit board.
The differential pair, Q1320-Q1322, responds to the
input signal when the voltage rises above (+ SLOPE) the
reference voltage at the base of Q1320. This reference
voltage is established by divider network R1312 and
R1314, The position of S1400D, SLOPE switch, determines whether a positive or negative going input will
cause the amplifier Q1324 to conduct. When the threshold
level is exceeded and conduction starts, current flow
through the circuit causes a voltage to be developed
across R1322. This voltage is applied to the base of Q1324.
The output at the collector of Q1324 is a TTL compatible
waveform to drive the logic circuit, U1310. CR1320
provides temperature compensation for Q1324.
level set by the VAR 0 control, R550, it is clamped. Q1523
now draws exactly the amount of current that the positive
current source supplies. Because the square wave at pin 5
(Q) of U1600A drives the base of Q1511, the clamping
action only happens during the positive edge of the
triangle wave. On the negative transition, Q1523 is shut
off, and Q1511 is on. In this manner, the timing capacitor
voltage can be clamped at any desired positive level.
@
as long as this condition exists. As soon as the level at the
input connector drops below the threshold, the output
voltage of U1310A rises. This high level causes the
generator to again stop running when the phase clamp
reaches its threshold level at the end of the last complete
cycle.
In the FREE RUN mode, S1400A is positioned such that
pin 4 of U1600A is held low. The generator now outputs
continuous waveforms.
SINE SHAPER
The Sine Shaper is composed of three separate circuit
functions: a Transconductance Amplifier, the Shaper
Circuitry, and an Output Buffer.
Transconductance Amplifier. Emitter coupled tran-
sistors Q1210 and Q1212 along with current source Q1200
form the Transconductance Amplifier. The amplifier con-
verts the triangle voltage at the base of Q1212 to a
differential current. This current flows through two sets of
diode wired transistors, U1120C, U1120D, U1220C, and
U1220D, to the input of the shaper.
Three modes of operation are selectable with S1400;
Triggered, Gated, and Free Running.
In the TRIG mode, S1400A and S1400C are positioned
such that the output, pin 6, of U1310B is connected to pin
4, set input, of U1600A. In this mode, a very narrow,
negative going voltage pulse is developed by U1310B each
time the input waveform passes through the trigger
threshold. This low sets U1600A, which deactivates the
phase clamp until the triangle generator again starts in the
positive direction, and allows the generator to complete
one full cycle.
In the GATE mode, S1400A and S1400C are positioned
such that the output, pin 3, of U1310A is connected to pin
4, set input, of U1600A. In this mode, a low level is
produced whenever the input waveform exceeds the
threshold if + SLOPE is selected. The generator free runs
Shaper. The active portion of the Shaper is formed by
two sets of emitter coupled transistors U1220A, U1220B,
U1120A and U1120B. These devices have their inputs
wired in series and their outputs cross coupled. U1120E
and U1220E are current sources for these devices. The
circuit operates by generating a power series approximation to the sine function. The devices in U1120 generate
the first order term while those in U1220 generate the
second order term in the approximation.
Output Buffer. The Output Buffer is an operational
amplifier that converts the differential current from Q1010
and U1020D to a single ended voltage that is applied,
through the function switch, to the output amplifier.
U1020E is a current source for the emitter coupled
differential input pair U1020A and U1020B. Q1012 serves
as a current mirror for U1020A and as an active load for
U1020B. U1020C is the output emitter follower and R1020
is the feedback resistor.
3-3
TM 9-6625-474-14&P-2
OUTPUT AMPLIFIER & ATTENUATORS
The output amplifier is basically a noninverting
operational amplifier whose plus input is the base of
Q2101 and minus input is the base of Q2113.
The three basic waveforms are selected by S1901 and
applied across R560B and R2335 to the input stage of the
amplifier. R560B varies the amplitude of the selected
waveform. The feedback network consists of R2011 and
R2012, connected from the output to the minus input of
the amplifier. C2011 provides high frequency compensation for the feedback, and is used to adjust the squarewave
front corner. The input pair, Q2101 and Q2113, amplify the
difference between the input waveform and the fedback
waveform.
An offset current is also summed with the feedback
signal at the base of Q2113 when S510A is closed. This
allows R560A to control the dc offset of the output signal.
POWER SUPPLY
The FG 501A receives its power from the power module
via interface connections on the rear edge of the Main
circuit board. The power module supplies plus (+) and
minus (–) 33.5 Vdc (unregulated) from which the following regulated voltages are generated.
+20 V SUPPLY
The +33.5 V from the power module is filtered and
applied to voltage regulator U1210 (pins 11 and 12). This
regulator contains its own reference, operational
amplifier, and current Iimiting elements. The output of the
regulator is applied to Q1231 which serves as a driver the
the series pass transistor located in the power module.
The +20 V output is applied across voltage divider R1201,
R1301, and R1315. The output level of the supply is set by
R1301 (+15 V Adj) which compares the supply output to
the internal reference level of the regulator. This supply is
current limited through the action of R1121 and the
current limiting element in the regulator. When excessive
amounts of current are drawn from the supply, the voltage
developed across R1121 turns on the current limiting
element in the regulator (U1210). This action reduces the
base drive, through Q1231, to the series pass transistor
causing the supply to reduce output, This supply is the
reference for other supplies in the FG 501A.
@
The output of Q2101 is applied directly to Q2111 which
is cascoded with Q2011. The output of Q2113 passes
through an inverting amplifier, Q2211, before passing to
Q2213 cascoded with Q2311. CR2111 provides temperature compensation for Q2211. The two cascodes form
drivers for the amplifier output stage.
The output stage consists of Q2013 and Q2123 in
parallel with Q2121 for amplification of positive going
signals. Q2321 and Q2323 in parallel with Q2325 form the
amplifier for negative going signals. The output is taken at
the junction of R2026 and R2228. The 50
impedance is determined by parallel 100
R2033 and R2131. C2121 in this network provides high
frequency compensation for the output impedance, The
attenuator circuit is a constant impedance resistive divider
network, switch selectable in 20 dB steps.
f2
output
Q
resistors
@
+20 V supply. Since this supply is sourced from the +20 V,
it is inherently current limited by the +20 V supply.
+5 V SUPPLY
The +5 V supply consists of U1230C and Q1331.
U1230C serves as an error amplifier which compares the
+5 V output to a +5 V reference developed by divider
network R1231, R1232 and R1233 from the +20 V supply.
Since this supply is sourced from the +15 V and referenced
to the +20 V supply, it is inherently current limited under
the same conditions that limit those supplies.
–20 V SUPPLY
The –20 V supply is derived from –33.5 V supplied by
the power module. The output of operational amplifier
U1230A is applied, through Q1245, to the base of Q1241,
which serves as a driver for the series pass transistor
located in the power module. This supply is also referenced to the +20 V. The supply is current limited through the
action of R1141 and Q1243. When excessive amounts of
current are drawn through R1141, a voltage sufficient to
turn Q1243 on develops across R1141. This action reduces
the base drive to the series pass transistor causing the
supply to reduce output.
–15 V SUPPLY
+15 V SUPPLY
The +15 V supply consists of U1230D and Q1221.
U1230D serves as an error amplifier which compares the
F15 Voutput of the supply to a +15 Preference developed
by divider network R1231, R1232 and R1233 from the
3-4
The –15 V supply consists of operational amplifier
(U1230B) and a series pass feedback regulator (Q1345),
The output of the supply is fed back through divider
network R1247, R1341, and R1245. The output level is
adjusted by R1341. Because this supply is sourced from
the –20 V supply, it is current limited by the –20 V supply.
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