Tektronix 7A22 User manual

Tektronix, Inc .
P
.O . Box 500
Beaverton, Oregon

97077
070-0931-00
Product Group 42
CHECK FOR CHANGE
INFORMATION
REAR O THIS MANUAL .
COMMITTED TO EXCELLENCE
N
MANUAL
Serial
Number
First
Printing JUL 1969
Revised SEP 1986

Copyright C
1969 Tektronix, Inc
.
All rights reserved .
Contents of this publication may
not
be reproduced
in any
form without the written permission of
'Tektronix, Inc
.
Products of Tektronix, Inc . and its subsidiaries are covered
by U .S .
and foreign patents and/or pending patents .
TEKTRONIX, TEK, SCOPE-MOBILE, and

T 4 are
registered
trademarks of Tektronix, Inc . TELEQUIPMENT
is a
registered trademark of Tektronix U .K . Limited .
Printed in U .S .A .
Specification and price change privileges
are reserved .
INSTRUMENT SERIAL NUMBERS
Each instrument has a serial number on a panel
insert,
tag,
or stamped on the chassis . The
first
number or letter
designates the country of manufacture .
The
last
five digits
of the serial number are assigned sequentially and are
unique to each instrument . Those manufactured
in
the
United States have six unique digits . The country of
manufacture is identified as follows :
B000000

Tektronix, Inc ., Beaverton, Oregon, USA
100000

Tektronix Guernsey, Ltd ., Channel Islands
200000

Tektronix United Kingdom, Ltd ., London
300000

Sony/Tektronix, Japan
700000

Tektronix Holland,
NV, Heerenveen,
The
Netherlands

Section 1
REVSEP 1981
Section 2
Section 2

OPERATING INSTRUCTIONS
(cont)
7A22
Page
Voltage Measurement
. .............

2-4
Signal Input
Connectors ..... . ......

2-4
High Input Impedance . .............

2-5
Display Polarity .... . ........ . ......

2-5
Deflection Factor . . . . . ...... . ......

2-5
Bandwidth Selection ...... . ........

2-5
Voltage Comparison Measurements ...

2-10
Differential Operation ........ . ...... 2-10
DC Offset Operation ...... . . ...... .

2-11
Input Overdrive Indicator ... . ....... .

2-12
Readout . . . ...... . ...... . ........ 2-12
Trace Identify .......... . ........

2-13
The remaining portion
of this Table of Contents lists the
servicing instructions .
These
servicing instructions
are
for
use by qualified personnel only . To avoid electrical shock,
do notperform any servicing other than that called out in the
operating instructions unless qualified to doso .
Section 3
Page
SPECIFICATION
Introduction ................. . ..... 1-1
Electrical Characteristics
.... . . ...... 1-1
Deflection Factor . ....... . ....... 1-1
Gain . . . ...... . . ...... . . ....... 1-1
Differential Dynamic Range . ...... 1-1
DC Offset ..... . ....... . . ....... 1-1
Frequency Response ... . . ....... 1-1
Bandwidth Limit . ....... . . ....... 1-1
Recovery Time . . ........ . ....... 1-1
Common-Mode
Signal Range
.... . 1-1
Common-Mode Rejection Ratio ... . 1-1
Maximum Input Voltage . . . ...... . 1-3
Input R
and C ............... . . .
1-3
Maximum Input Gate Current
... . . .
1-3
Variable Balance
...... . ........
. 1-3
Step Attenuator DC Balance
... . . .
1-3
Displayed Noise (Tangentially
Measured) . . . ............... . . . 1-3
DC Drift .... . ....... . ....... . . . 1-3
Isolation Between
+
and ---
Inputs ..... . . ....... . ...... ... . 1-3
Environmental Characteristics .... . . . . 1-3
Altitude .... . . ....... . ...... . . . . 1-3
Transportation ...... . . ...... . . . . 1-3
Physical Characteristics . . . ...... . . . . 1-3
Finish ..... . . .............. . . . . 1-3
Dimensions . . ...... . ....... . . . . 1-3
Weight .... . . ...... . . ....... . . . 1-3
OPERATING INSTRUCTIONS
Introduction .. . .
. ...... . ........
. . . 2-1
Front Panel
Controls and Connectors . 2-1
Operating Instructions
........... . . .
2-2
First Time Operation
. . ........ . . .
2-2
General Operating Information . . . .... 2-4
Trace Drift ....... . ........ . .... 2-4
Input Gate Current ...
. . ............
2-4
CIRCUIT DESCRIPTION
Introduction ............ . ...... . . . . 3-1
Block Diagram Description ...... . . . . 3-1
Input Coupling ....... . ...... . . . . 3-1
Input Attenuators .... . ...... . . . . 3-1
Preamp ......
. ........ . .... . . . .
3-1
L
F ---3
dB
Point
............ . . . .
3-1
Output Amplifier ..... . ...... . . . . 3-2
HF --3 dB
Point
..... . ...... . . . . 3-2
General
Information
............ . . . . 3-2
Feedback Amplifiers
. . ....... . . . .
3-2
Differential Configuration
..... . . . .
3-3
Detailed
Circuit Description
...... . . . .
3-3
Input Coupling
. ...... . ...... . . . .
3-3
Input Attenuators ........... . . . . 3-4

7A22
SECTION 4
SECTION 3
REV C, MAR 197 9
CIRCUIT DESCRIPTION (cont)
Page SECTION 4
MAINTENANCE (cont) Page
Gate Current Compensation . 3-4
Special Parts
....... .... . 4-2
Input Amplifier ... .
....... 3-4 Soldering
Techniques ...... 4-2
X15 Preamp . .... . . .... 3-4
Component Replacement
Information ......... ....
4-3
DC Balance . .......... 3-4
Troubleshooting ............
4-5
Floating Power Supply ... 3-5
Introduction .............
4-5
Common-Mode Rejection .
3-5
Indicator Oscilloscope ..... 4-5
Cross Neutralization . ....
3-6
Operating Procedure and
Input
Overdrive Protection 3-7 Control
Settings . . .
. ...... 4-5
DC
Offset
............
3-7
Trouble Symptoms .
.... ... 4-5
Offset Generator ....... 3-7 Visual
Inspection .........
4-5
Input Overdrive Indicator .
3-8
Calibration Check ........
4-5
L F --3 dB Point Selector
. 3-9
Detailed Troubleshooting . . ...
4-5
Output Amplifier ......... 3-9
Test
Equipment Recommended 4-6
Gain Switching Amplifier
. 3-9
DC Balance Check ........ 4-6
Variable Output
stage . ... 3-11
Troubleshooting by Direct
Signal Output Amplifier . . 3-11
Replacement
............ 4-6
Trigger Output Amplifier . . 3-11
Components Checks ......
4-6
Indicator Oscilloscope Readout 3-11
Transistors ...........
4-6
Probe Sensing .........
3-11
Diodes . .... .........
4-8
Trace
Identify ......... 3-11
Resistors . . ... . ... .... 4-8
Capacitors .... ..... ..
. 4-9
MAINTENANCE
Repackaging
for Shipment . ... 4-9
Introduction ...............
4-1
Preventive Maintenance
...... 4-1
General
4-1
SECTION 5 PERFORMANCE
CHECK/
................
CALIBRATION
PROCEDURE
Cleaning
Front Panel ...... 4-1
Introduction ...... ......... 5-1
Cleaning Interior .........
4-1
Test Equipment
Required . . ... 5-1
Visual Inspection
. . ....... 4-1
General ................
5-1
Transistor Checks
..... . . . 4-1
Short Form Procedure ....... 5-2
Calibration ..............
4-1
Performance Check/Calibration
Corrective Maintenance ......
4-1
Procedure ............. ...
5-3
General . .... . . .........
4-1
General
................
5-3
Obtaining Replacement Parts 4-2
Preliminary Procedure
..... 5-3

SECTION 5
REV
B, MAR 197 9
Conpensation ... . . ....
5-9
-Input Atten
Compensation 5-9
---Input
Atten Shunt
Compensation ......... 5-10
H F -3dB Point ........

5-11
Abbreviations
and symbols used in this manual are based on or
taken
directly from IEEE Standard 260 "Standard
Symbols for
Units", MIL STD-12B and other standards of
the electronics
industry . Change information, if
any,
is
located atthe rear of this
manual .
PERFORMANCE
CHECK/
CALIBRATION
PROCEDURE
(cont)
Page
L F ---3 dB Point . . ......

5-11
CMRR ..............
. 5-12
Input Overdrive
Indicator . 5-12
Differential
Dynamic Range 5-13
Overall Noise Level
(Measured
Tangentially) . . 5-13
Overdrive
Recovery Time .

5-14
ELECTRICAL PARTS
LIST
Abbreviations and Symbols
Parts Ordering Information
Index of Electrical
Parts List
Electrical
Parts List
DIAGRAMS AND MECHANICAL
PARTS ILLUSTRATIONS
Diagrams
Mechanical
Parts Illustrations
MECHANICAL PARTS LIST
Mechanical Parts List
Information
Index of
Mechanical Parts
Illustrations
Mechanical Parts List
Accessories
7A22
PERFORMANCE CHECK/
SECTION 5
CALIBRATION PROCEDURE
(cont)
Page
Check or Adjust ..........
5-4
AC
Step Atten Balance . . .
5-4
Variable Balance .......
5-4
Coarse
DC Balance
.....
5-4
+ Gate Current Zero .....
5-5
---- Gate Current
Zero ..... 5-5
GAIN ...............
5-5
VARIABLE Control Ratio . .
5-5
VOLTS/DIV Gain Switching
5-5
SECTION 6
Isolation between
4- and --
Inputs
. ........... . . . 5-6
Total DC Offset Range ... 5-6
C241 +Cross Neutralization
5-7
C141 --Cross Neutralization
5-7
C115 X1 -I-Input
Atten Time
Constant
. . . . ......... 5-7
SECTION 7
C215 X1
-Input Atten Time
Constant . ............
5-7
Input Atten Accuracy ....
5-8
Input Atten
Differential
Balance ..............
5-8
SECTION 8
--l-Input Atteh Series

Type
7A22
Fig . 1-1 . Type
7A22 Differential Amplifier .

Introduction
The Type
7A22 Vertical Plug-in is a DC coupled differ-
ential
amplifier with excellent common-mode rejection char-
acteristics
and high gain for low level applications .
The
DC Offset capability of the Type 7A22 allows the
display
of the very small low-frequency signals
containing
a large
DC component, at deflection factors not possible
with
AC coupling
.
The vertical deflection factor range of the
Type
7A22 is from 10/W to 10 V .

The high and
low fre
quency --3 dB

points can

be selected at the front
panel,
to set the bandwidth of the instrument . Thus, for
low fre-
quency applications the signal-to-noise
ratio can be improved
by restricting the bandwidth of the Type
7A22 . The band-
width selection and excellent drift-with-time characteristics
provide measurement
capabilities in the biomedical, trans-
ducer, and other areas which
require stable, low deflection
factor, low noise measurements .
The Type7A22 is designed for
use in Tektronix 7000 Series
oscilloscopes .
The electrical
characteristics described in this section are
valid over the stated
environmental range for instruments
calibrated at
an ambient temperature of +20'C to +30 ° C
and after a5
minute warmup unless otherwise noted .
ELECTRICAL CHARACTERISTICS
Characteristic
Deflection Factor
(VOLTS/DIV)
Gain Ratio
Accuracy
VAR (CAL IN) Range
Differential Signal Range ^
(DC OFFSET' not used)
10 ~tV/Div to
10 mV/Div
20 mV/Div to
0 .1 V/Div
0 .2 V/Div to
1 V/Div
2 V/Div to
10 V/Div
Change
information, if any, affecting this section will
be found at the
rear of the manual .
Performance Requirements
Within 2% with GAIN adjusted at
1 mV/div
Continuously variable ; extends de-
flection factor to at least 25 V/div
Permits adjustment of deflection
factor at 1 mV/DIV for all main-
frames
At least _F_-1 V
At least J-10 V
At least
--1-100V
At least 4-1000V
DC OFFSET
COARSE Range from
Electrical Zero
10 [tV/Div to
10 mV/Div
20 mV to 0 .1
V/Div
2 V to 10 V/Div
Frequency Response (8
div Reference)
Overall Frequency
Response DC (Direct)
Coupled Input
AC (Capacitive) Cou-
pled Input Lower
Bandwidth Frequency
Bandwidth Limit
Accuracy
HF ---3 dB POINT
100 Hz to 1 MHz
Accuracy
LF
-3 dB POINT
0 .1 Hz to 10 kHz
20 mV/Div to
0 .1 V/Div
0 .2
V/Div to
10 V/Div
Common-Mode
Rejection Ratio
DC (Direct) Coupled
AC (Capacitive)
Coupled
Type 7A22
At least
+100V
to
-100V
At

least

+1000V

to

--1000 V
------ - --- -- -----------

- ------
Within 10% of selected frequency
6 steps in a 1-10 sequence
10 /us or less to recover to within
0 .5% of zero level after the re-
moval of a
+
or --- test input
ap-
plied for 1 s . Test signal not
to ex-
ceed Differential Signal Range .
Specified aberration
(0 .5%) based
on test signal amplitude
At
least +10V and -10V
At least +100V and -100V
At least +500V and ----500V

0 'o
CMRR
x m m a
10
3
n 0 3 3 0 3 0 a
10
Hz

100
Hz

1
kHz

10
kHz 100 kHz

1
MHz
m
Verification
Points
Q O 3
T
a N N
N n 3

ELECTRICAL CHARACTERISTICS (cont)
Characteristic v
Maximum Input Voltage
(each input)
DC (Direct) Coupled,
DC
-f-
Peak AC, AC
Component 1 MHz or
less
10 ttV/Div

to

10
mV/Div
20 mV/Div

to

0 .1
V/Div
.2 V/Div

to

10V/
Div
AC (Capacitive)
Coupled
Input DC Voltage
AC (Capacitive)
Coupled
Input DC Rejection
Input R and
R
C
__
Resistance
Capacitance
R
& C
Product
Maximum Input Gate
Current
10 [,V/Div to

10 mV/
Div
Displayed - Noise
(Tan-
getially Measured)
20
mV/Div to 10V
Div
Display Shift at 10 ttV
/Div
(AC
Coupled)
Variable Balance
_
Performance _ Requirements 'N `-
-j-_ 15 V
-1-200 V
-A-500 V
-+500V, each input
At least 4 X 10 5 :1
0 .2 T div ^ or less shift with VARIABLE
control turned from fully cw to
fully ccw position
16,utV or 0 .1 Div (whichever is
greater), 1 MHz HF ----3 dB POINT,
source resistance 250 or less
DC Drift
Drift with Time (Ambi-
ent Temperature and
Line Voltage Constant)
Short Term
Drift with Ambient
Temperature (Line
Voltage Constant)
Isolation between
-I-
and
-- Inputs
(+
INPUT to
an Open - INPUT, --
INPUT to an Open
INPUT)
Long Term
Finish
' Dimensions
Weight
ITEM
Specification-Type 7A22
5 tkV (P-P) or 0 .1

div (whichever
is greater) in any minute after 1
hour warmup
10 ~tV (P-P) or 0 .1 div (whichever
is greater) in any hour after 1
hour warmup
501AV/ ° C or less
At least 200
:1,
DC to
1 MHz
____ _CHARACTERISTIC
Front panel is anodized aluminum
___N_~4%
inch L
X
2% inch ^ W X
-z 2 5 / 8 Ibs
1 MQ ZL .
1
Approximately 47 .0 pF
Within between all de-
PLUG-INTESTED
ENVIRONMENTAL
OUTOF
INDICATOROSCILLOSCOPE
CHARACTERISTIC
flection factors
_
Altitude
x-25°C____
+50C __- .--
Non-operating To 50,000 feet
and --55°C
Transportation Qualified
under National Safe
-f-20 pA -t=100 pA each input
Transit Committee test procedure
-+-40 pA -±-=200 pA Differentially
1A,
Imo_ . . ... ._ .__ . .___ .___
Category I I
-+-_ 10 pA -t :-20 pA
___ . ._ . .__ . ._ ._ . . .
.±-4
div :+-20 div
PHYSICAL

Introduction
Change information, if any, affecting this section will
be
found at the
rear of the manual .
This section opens with a brief functional description of
the front-panel controls, input overdrive lamp, and input
connectors . Following the front-panel description is a familiar-
ization procedure and finally a general discussion of the
operation of the Type 7A22 .

-f-
INPUT
CONTROLS AND CONNECTORS
INPUT

Input overdrive indicator lamp turns on
OVERDRIVE

to
indicate
excessive differential drive
to the input amplifier
stage . Lights when
the differential dynamic range
between
input connectors is exceeded .
VOLTS/DIV

Volts per displayed division . Nineteen
position switch used to select the cali-
brated deflection factors .
VARIABLE

Two-position
switch activated by the
(CAL IN)

VARIABLE
knob to select calibrated or
uncalibrated deflection factors . At the
IN
position, the VARIABLE
control is in-
operative and the deflection factor
is
calibrated . When pressed and released,
the knob moves outward to activate the
VARIABLE control for
uncalibrated de-
flection factors
.
The uncalibrated posi-
tion provides continuously variable un-
calibrated attenuation between the cali-
brated deflection factors and extends
the deflection factor to at least 25
VOLTS/DIV .
GAIN

Screwdriver adjust control to set the CRT
display scale factor to agree with the
VOLTS/DIV switch indication . Adjusted
for proper deflection with the VOLTS/
DIV switch set to the 1 mV position .
POSITION

The control that vertically positions the
trace or display .
IDENTIFY

Momentary contact, push-button switch,
concentric with POSITION . Will cause
the trace, representing the output of the
Type 7A22, to move a small amount
when pressed . Aids in identifying the
Type 7A22 trace when multiple traces
are displayed .
HIGH

Nine position switch to select the ap-
FREQUENCY

proximate
high frequency
----3 dB
point .
----3 dB POINT - The switch positions are : 100 Hz, 300 Hz,
1 kHz, 3 kHz, 10 kHz, 30 kHz, 100 kHz,
300 kHz, and 1 MHz
.
LOW

Eight position switch to select DC coupl-
FREQUENCY

ing or the approximate low frequency
-3 dB POINT

----3 dB points . The switch positions are :
DC OFFSET, DC, .l Hz, 1 Hz,

10 Hz,
100 Hz, 1 kHz, and 10 kHz .
-- INPUT
J_
INPUT WAVEFORM
AC-GND-DC
Type 7A22
Signal input connector . Positive input
produces deflection upward (see Fig .
2-1) .
Signal input connector . Positive input
produces deflection downward (see
Fig .
2-1) .
Fig . 2-1 . Signals applied to the +INPUT
connector produces an
upright display,
while
signals
applied to the --INPUT are inverted .
A miniature illuminated push-button
type
switch . The buttons are
interlocked so
that only one button may be
depressed
at one time . When the 'AC' button is
depressed the signal is coupled through
0 .1'cF to the Input Amplifier and only
the varying component of the input sig-
nal is amplified .
When the 'DC' button is depressed the
signal is coupled directly to the Input
Amplifier and the entire input signal,
both
AC
and DC, is amplified . When
the 'GND' button (or none of the but-
tons) is depressed, the signal is coupled
through 0 .1 al` and through 1 M52 to
ground . The Amplifier Input is grounded
in this condition .

Operating Instructions----Type 7A22
--- AC-GND-DC

Same function as the
-I-
AC-GND-DC
switch but applied to
the
,--- INPUT .
The following two controls are operative only
when the LOW FREQUENCY ---3 dB POINT switch
is set to DC or DC OFFSET .
STEP ATTEN

Front panel control for DC balancing
DC BAL(DC MODE the amplifier input stage . With no sig
ONLY)

nals applied to the input connectors,
the control is adjusted for no trace
shift as the VOLTS/DIV switch is moved
from the 10
mV
position to the 10 [V
position .
DC OFFSET

Coarse and fine controls to provide
(DC OFFSET

internal offset bias while maintaining
mode only)

the
differential capability
. Available
range of
the
offset bias depends upon
the settings of the VOLTS/DIV switch,
and is indicated by shaded gray bands
(OFFSET RANGE) around the VOLTS/
DIV switch .
RELEASE LATCH

Gray rectangular knob near the bottom
left of the front panel . Pull out to re-
move Plug-In from Plug-In compartment .
OPERATING INSTRUCTIONS
First-Time Operation
Each push-button is illuminated from
behind when the button is depressed .
IMPORTANT
Steps 1 through 5 in the following procedure are intended
to help place the trace on the screen quickly and prepare
the unit for immediate use . Steps 6 through 8 are used to
check the GAIN adjustment . These steps along with those
remaining are intended to demonstrate some of the basic
functions
of
the Type
7A22 .
1 . Insert the unit into the oscilloscope plug-in compart-
ment .
2 . Set the Type
7A22 front-panel controls as follows :
VOLTS/DIV

1
mV
VARIABLE

IN (CAL)
POSITION

Midrange
HIGH FREQUENCY

1 MHz
--3 dB POINT
LOW FREQ ---3 dB POINT

DC
AC-GND-DC
(-h-
INPUT)

GND
AC-GND-DC (, INPUT)

GND
STEP ATTEN DC BAL

Midrange
3 . Turn the oscilloscope Intensity control fully counter-
clockwise and turn the oscilloscope Power ON . Preset the
time-base and triggering controls for a .5 ms sweep rate
and automatic triggering .
4 . Wait about five minutes for the Type 7A22 and the
oscilloscope to warm up .
2-2
NOTE
About five minutes is sufficient time for warmup
when using the Type 7A22 for short-term DC meas-
urements . For long-term DC measurements using
the lower deflection factors, allow at least one
hour .
5 . Adjust the Intensity control for normal viewing of
the trace . The trace should appear near the graticule center .
6 . Using the POSITION control, position the trace 2 divi-
sions below graticule center .
CAUTION
If the maximum input
voltage
rating in the 10 ~tV
to 10 mV range of the VOLTS/DIV switch is ex-
ceeded, the inputs are diode-clamped to
fixed
voltages of approximately
+
16 .5 volts
and/or
--16 .5 volts and damage to the signal source is
possible . If the signal source cansupply more
than
1/16 A of current, the input protective fuse(s)
will open . An open input fuse is indicated by the
lighting of the INPUT OVERDRIVE indicator with the
input coupling switches set to GND .
7 . Apply a 4 mV peak-to-peak calibrator signal through
a coaxial cable to the -¢- INPUT connector on the Type
7A22 .
8 . For DC coupled, single-ended operation, set the
INPUT AC-GND-DC coupling switch to DC . The display
should be square waves 4 divisions in amplitude with the
bottom of the display at the reference established in step 6 .
9 . For AC coupled, single-ended operation, reposition the
display with the
Type 7A22 POSITION control
to place the
bottom of the display at the graticule center line .
10 . Set the
-f-
INPUT AC-GND-DC coupling switch to AC
and note that the display shifts downward about 2 divisions
to its average level .
11 . Disconnect the coaxial cable from the -¢- INPUT con-
nector . Connect a dual input connector to the -¢- INPUT
and -- INPUT connectors . Connect the coaxial cable from
the Calibrator to the dual input connector .
12 . For AC coupled differential operation, set the
-INPUT AC-GND-DC coupling switch to AC . The cali-
brator signal is now coupled to both inputs as a common-
mode signal . A straight line display should be observed,
since the common-mode is being rejected .
Operational Adjustments
NOTE
Most of the following checks and adjustments may
be made after a 5 minute warmup ; however due
to the DC drift of the amplifier during subsequent
warmup, the STEP ATTEN DC BAL should be re-
adjusted for each check or adjustment, and a
warmup of at least one hour should be allowed
before a final adjustment of the STEP ATTEN DC
BAL is attempted . Insure that the oscilloscope used
in conjunction with the Type 7A22 is correctly cali-
brated (refer to the oscilloscope manual) and that
the calibrated output voltage is correct .

1 .
AC ATTEN BAL (internal adjustment) . When the
LOW FREQ ---3 dB POINT switch is used to limit the low
frequency response of the Type 7A22, the unit employs
AC stabilization . This means that when the switch is set
to any position except DC or DC OFFSET, the STEP ATTEN
DC BAL and DC OFFSET controls become inoperative .
VOLTS/DIV balance is then controlled with the
AC
ATTEN
BAL, an internal adjustment (see Fig . 2-2) .
Fig . 2-2 . Location of AC ATTEN BAL control .
When transferring the Type 7A22 from one oscilloscope
to another, it may be necessary to perform a minor re-
adjustment of this control, due to normal power supply vari-
ations between oscilloscopes .
NOTE
An unbalance of up to 30 I,V is normal and can-
not
be reduced
by
adjusting the AC ATTEN
BAL
control .
a . With the Type7A22 inserted into the oscilloscope, re-
move the left side panel
of
the oscilloscope and set the
Type
7A22 controls as follows :
VOLTS/DIV

1
mV
AC-GND-DC (-+-INPUT)

GND
AC-GND-DC (---INPUT)

GND
LOW FREQ -3 dB POINT

10 Hz
HIGH FREQ --3 dB POINT

100 Hz
b . Using the POSITION control, position the trace to
graticule center .
d . Adjust the AC ATTEN BAL control, R505, to position
the trace to within 1 .5 divisions of graicule center . (See
note in step 1) .
c .

Set the VOLTS/DIV switch to 20 ~tV .
INTERACTION : If this adjustment is made out of se-
quence, steps 2 and 3 must also be performed .
Operating Instructions-Type
7A22
2 . VAR BAL
R425 .
(Internal
adjustment) .
a .
Set the Type7A22 controls as in step 1-a .
b . Position the trace to graticule center with the POSI-
TION control .
c . With the VAR (CAL IN) in the out position, rotate the
VARIABLE control from stop to stop . Check for no move-
ment of trace .
d . Adjust R425 for no movement of trace
as
the VARI-
ABLE control is rotated from stop to stop .
(See
Fig . 2-2 for
location of adjustment .)
3 . STEP ATTEN
DC BAL
.
With zero
input voltage and
the
LF ---3 dB POINT selector at DC, if the STEP ATTEN
DC
BAL
is not properly adjusted the CRT trace will shift
vertically as
the VOLTS/DIV switch is rotated throughout
its range . The shift is more noticeable at the most sensi-
tive
positions .
a . Set the Type 7A22 front-panel controls as follows :
VOLTS/DIV

10 mV
VARIABLE (CAL IN)

CAL
POSITION

Midrange
HIGHFREQ ---3 dB POINT

1 MHz
LOW FREQ -3 dB POINT

DC
AC-GND-DC (-(-INPUT)

GND
AC-GND-DC (----INPUT)

GND
STEP ATTEN DC BAL

Midrange
b . Using the Type 7A22POSITION control, position the
CRT trace to the center of the graticule
.
c .

Set the
VOLTS/DIV
switch to 10 ttV .
d . Return the trace to graticule center by adjusting the
STEP ATTEN DC BAL control .
NOTE
The adjustment of the STEP ATTEN DC BAL con-
trol should be checked periodically during the use
of the instrument . If the Type 7A22 is used DC
coupled or in significantly varying ambient tem-
peratures in the 10 ,uV/DIV to .1 mV/DIV ranges,
the STEP ATTEN DC BAL should be checked quite
frequently . It is good practice to check this con-
trol and readjust, if necessary, before any critical
measurement is
made
under the above conditions
.
4 . GAIN
a . Perform steps 1 through 8 in the First-Time Operation
Procedure .
b .
Adjust the GAIN control
for exactly 4 divisions of
display .
NOTE
Accuracy of this adjustment is dependent upon the
voltage accuracy of the calibration source .
2- 3

Operating Instructions---Type 7A22
Trace Drift
The environment in which the Type 7A22 is operated and
the inherent characteristics of the Type 7A22 influence trace
drift . Therefore, to determine trace drift for a specific en-
vironment refer to the Specification
Section
.
In environment
in which the ambient temperature
does not vary much (such
as an air-conditioned building) the trace drift generally will
not exceed
101tV
in one
hour
.
Input Gate Current
When using the .1
mV/DIV to 10 ttV/DIV ranges for meas-
urement with an AC coupled input, for
DC measurements
where the
source impedance is high (in excess of 1 MQ) the
input gate current
should be checked and allowed for, or
adjusted to zero . This
is
particularly
desired at high tem-
peratures
(above 40°C)
.
Steps 7 and 8 in the Performance
Check/ Calibration Procedure describe the
check and adjust
procedures for setting the gate
current to zero .
Voltage Measurement
To obtain accurate DC measurements at maximum sensi-
tivity,
it is necessary to ground the input and DC balance
the
amplifier just before making the measurement . This is
accomplished by adjusting the STEP ATTEN DC BAL as
described under operational adjustment number 3 .
When
measuring DC voltages, use the largest deflection
factor (10 V/DIV) when first connecting the Type 7A22 to
an unknown voltage source . Then, if the deflection is too
small to make the measurement, switch to a lower deflec-
tion factor . If the input stage is overdriven, a large amount
of current might flow into the input . See CAUTION after
item 6 of First Time Operation .
Where only the AC component of a signal having both
AC and DC components is to be measured, use the AC-
GND-DC switches to take advantage of the pre-charging
circuit incorporated in the unit . The pre-charging circuit
permits the coupling capacitor to charge to the DC source
voltage when the AC-GND-DC switch is set to GND . Pro-
cedure for using this circuit is as follows :
a . Before connecting the Type 7A22 to a signal contain-
ing a DC component, set the AC-GND-DC input coupling
switch to GND . Then connect the input to the circuit under
test .
b . Allow about one second for the
coupling capacitor to
charge .
b .
Set
the
input coupling switch to AC . The display will
remain on the
screen and the AC component can be meas-
ured in the
usual manner
.
d . On completion of the measurement, set the AC-GND-
DC switch to GND and short the input connector to ground .
The above procedure
should be followed
whenever an-
other signal with a different DC level is connected .
2-4
GENERAL OPERATING INFORMATION
CAUTION
If the Type 7A22 is connected to a large DC volt-
age source without using the pre-charge provi-
sion, the peak charging current (into 0 .1 al`
capacitor) will
be limited only by the signal
source, and this
source may be damaged or de-
stroyed .
When a large
DC
voltage has
been applied to the Type
7A22 with the input AC coupled, the input coupling capaci-
tor acquires a charge due to dielectric polarization and acts
as a low voltage, high impedance voltage source with a
very slowly decaying output voltage . This can offset sub-
sequent
AC coupled measurements at other DC voltages
and drive the trace off-screen . A period of at least 10 min-
utes, with input set to GND, should be allowed to assure
reasonable recovery from polarization, and a longer period
may be necessary for critical measurements . If the input
connectors are shorted to ground the depolarization proc-
ess will require less time .
Signal Input Connectors
When connecting signals to the -{-INPUT and ---INPUT
connectors on the Type 7A22, consider the method of cou-
pling that will be used . Ordinary unshielded
test
leads can
sometimes be used to connect the Type7A22
to
a signal
source, particularly when
a high level, low-frequency signal
is monitored at a low impedance point . However
when
any
of these factors are missing,
it
becomes increasingly im-
portant
to use shielded signal cables . In all cases, the signal-
transporting leads should
be kept as short as practical .
When making single-ended input
measurements, be sure
to establish
a common ground between the device under
test and the Type 7A22
. The shield of a coaxial cable is
normally
used
for this
purpose .
In some
cases differential measurements require no com-
mon ground', and therefore
are less susceptible to inter-
ference
by ground loop currents . Some problems with
stray magnetic coupling into the signal transporting leads
can also be minimized by using a differential rather than
single-ended measurement . These considerations are dis-
cussed later in this section under Differential Operation .
It is always important to consider the signal-source load-
ing and resulting change in the source operating character-
istics due to the signal-transporting leads and the input
circuit of the Type 7A22 . The circuit at the input connectors
can normally be represented by a 1 megohm resistance to
ground paralled by 47 pF . A few feet of shielded cable
may increase the parallel capacitance to 100 pF or more .
In many cases, the effects of these resistive and capacitive
loads may be too great and it may be desirable to minimize
them through the use of an attenuator probe .
Attenuator probes not only decrease the resistive and
capacitive loading of a signal source, but also extend the
measurement range of the Type 7A22 to include substanti-
ally higher voltages . Passive attenuator probes having at-
tenuation factors of
10X, 100X,
and
1000X, as well as
other
special-purpose types are available through your Tektronix
Field Engineer or Field Office .
Some measurement situations require a high-resistance in-
put to the Type 7A22 with very little source loading or sig-
- -------------------- -
'The DC plus peak AC voltages on the test points with respect
to the chassis potential of the Type 7A22 should
be
limited to
the levels listed in Section I under Maximum Common-mode Input
Voltage characteristics . Higher levels will
degrade
the
common-mode
rejection ratio and exceed the input voltage rating of the unit .

nal attenuation . In such a situation a
passive attenuator
probe cannot be used . However, this problem
may be solved
by using an active probe or the high input
impedance pro-
vision of the Type7A22 .
High
Input Impedance
The high input impedance provision applies only to
DC
coupled signals which permit the
use of 10 mV through 10
/AV positions of the VOLTS/DIV switch, (DC
coupled) . Since
no input attenuator is used at these switch
positions, the
internal gate return resistor alone
establishes the 1 megohm
input resistance .
The high input impedance is obtained
by unsoldering the
wire strap (see Fig . 2-3) between the
input line and the inter-
nal gate return resistance . The signal
source must then pro-
vide a DC path for the FET gate current .
Fig . 2-3
. Location of wire strap between input line and internal gale
return resistor
.
The
uncompensated gate current is typically less than 100
picoamperes, but
may be several times higher depending
upon the
operating temperature . The signal-source imped-
ance is therefore an important factor since gate current will
produce a DC offset . For example, a 100 picoampere gate
current through 10 megohms produces a 1
mV offset
;
this
may result in a significant error where small voltages are of
concern .
NOTE
When
the wire straps are removed, R 111 and R211
are disconnected
. The deflection factor in the 20 m Vl
DI V
to 10 VIDI V
range
will be incorrect .
The high-frequency response
will also depend upon the
signal-source impedance, since various shunt capacitances
between
the source and the 7A22 input as well as the 47 pF
input
capacitance, must charge and discharge through that
impedance (see Fig . 2-4) .
REV
.
B, FEB .
1975
Display Polarity
Deflection Factor
Noise
Bandwidth Selection
Operating Instructions Type
7A22
Single-ended signals
can be applied to either the -}-INPUT
or -INPUT connector .
If the +INPUT is chosen, positive-
going changes in the
input signal will cause the trace to be
deflected upward, and
negative-going changes will cause
the
trace to be deflected downward . If the
-INPUT is
chosen, input-to-display polarity relationship will
be reversed
as shown previously in Fig . 2-l .
The
amount of trace deflection produced
by a signal is
determined by the signal amplitude, the
attenuation factor
of the probe, the setting of the VOLTS/DIV
switch and
the
setting of the VARIABLE control . The calibrated
deflection
factors indicated by the VOLTS/DIV switch
apply only when
the
VARIABLE control is pushed "in" to the
CAL IN position .
The range of the VARIABLE control is at
least 2 .5 :1 . It pro-
vides uncalibrated deflection factors
covering the full range
between the fixed settings
of
the
VOLTS/DIV switch . The con-
trol can be set to extend the deflection
factor to at least 25
volts/div .
To reduce noise and
obtain a more usable display when
the VOLTS/DIV
switch is operated in the 10 [V, 20 ~tV, and
50
~tV positions or when the signal source is noisy, it is sug-
gested that the HIGH
FREQ -3 dB POINT selector be set
to use
the
lowest bandwidth setting which does not appreci-
ably
distort the desired features of the signal under observa-
tion . Refer to Fig . 2-6 for the high frequency rolloff for each
setting of the HIGH FREQ -3 dB POINT selector .
In addition to the differential rejection of unwanted signals,
many times an undesired signal can be attenuated by varying
the bandwidth of the unit . The LOW FREQ
-3
dB POINT
and HIGH FREQ -3 dB POINT selectors on the front panel
of the 7A22 control the low-frequency and high-frequency
-3 dB points of the amplifier . The LOW FREQ
-3 dB
POINT
selector provides low-frequency response to DC or to ap-
proximate -3 d8 points at .1 Hz, 1 Hz,
10
Hz, 100 Hz, 1 kHz,
and 10 kHz . Refer to Fig . 2-5 . The HIGH FREQ
-3
dB POINT
selector controls the high-frequency rolloff from 1
MHz to
100 Hz in a
1-3-10 sequence .

Beyond the -3 dB points the
frequency response falls off
at a 6 dB per octave rate . Refer
to Fig . 2-6 .
Varying the
bandwidth of the Type 7A22 is useful, for ex-
ample, when displaying
a low-frequency signal . By reducing
the high-frequency response
the noise can, in many cases, be
considerably reduced without
distorting the desired signal
(see Fig . 2-7) . Likewise,
undesired line-frequency signals can
be filtered
out by restricting the low-frequency response of
the unit . When using the
LOW FREQ -3 dB POINT and
HIGH FREQ -3 dB POINT selectors, care must be taken not
to distort
non-sinusoidal waveforms by overly restricting the
amplifier
bandwidth-
2-5

Fig .
2-4A . 7A22CMRR at 10 IV/Div to 10 mV/Div . Inputs DC Coupled . Worst-case degradation due to source resistance .
Operating Instructions---Type 7A22

Operating Instructions---Type
7A22
Fig . 2-4B . 7A22 Bandwidth and VOLTS/DIV Error as functions
of Source Resistance .
Z-7

Operating Instructions-Type 7A22
Fig .
2-5 . 7A22 FREQUENCY
RESPONSE as a function of LF ---3 dB POINT SETTING (HF ---3 dB POINT at 1 MHz) .
2MB

2-
9
Fig . 2-6 . 7A22 FREQUENCY RESPONSE as a
function of HF
.-- .3
dB POINT settings (LF --3 dB POINT of
DC) .
Operating Instructions---Type 7A22

Operating Instructions--Type 7A22
Fig . 2-7 . Improving signal-to-noise ratio by setting bandwidth .
(A) Lower --3
dB FREQUENCY selector to DC, UPPER -3 dB FRE-
QUENCY 1 MHz . (B) Lower
-3 dB FREQUENCY selector to DC,
UPPER
-3 dB FREQUENCY, 10 kHz .
Voltage
Comparison Measurements
Some applications require a set of deflection factors other
than the fixed values provided by the VOLTS/DIV switch .
One such application is
comparison of signal amplitudes by
ratio rather than by
absolute voltage .
To
accomplish this, apply a reference signal to either in-
put of the Type
7A22 . Set the VOLTS/DIV switch and VARI-
ABLE control throughout the
subsequent comparisons . The
settings of
the VOLTS/DIV switch can be changed, however,
to
accommodate large ratios . In doing so, regard the num-
bers which
designate the switch position as ratio factors
rather than voltages .
Differential
Operation
Differential
voltage measurements are made by apply-
ing the signals
to
the
-1 -INPUT and ---INPUT connectors .
Then, both AC-GND-DC switches should be set to the same
positions : AC or DC, depending on the method of signal
2-10
coupling desired . When using the Type .7A22 for differential
operation, only the voltage difference between the
two sig-
nals is amplified and displayed on the CRT . Common-mode
signals (signals that are common in amplitude, frequency
and phase) are rejected (see Fig . 2-8) .
The Type 7A22 differential input provision
may be used
to eliminate interfering signals
such as AC line-frequency
hum . Single-ended
measurements often yield unsatisfactory
information
because of interference resulting from ground-
loop currents between the
oscilloscope and the device under
test .
In other cases, it may be desirable to eliminate a DC
voltage by means other than the use of a DC-blocking capac-
itor which
would limit low-frequency response . These limi-
tations of single-ended measurements are virtually eliminated
in differential measurements .
A
differential measurement is made by connecting each
of the two inputs to selected points in the test circuit . The
input
to the amplifier will then be the difference in voltage
of the two selected points (see Fig . 2-9) .
The ability of the Type 7A22 to reject common-mode sig-
nals is indicated by the common-mode rejection ratio (CMRR) .
This ratio is at least 100,000 :1 at the input connectors for the
lower deflection factors (10 [kV to 10 mV per division) when
signals between DC and 100 kHz are DC-coupled to the in-
puts . To show the significance of this characteristic, assume
that a single-ended input signal
consists of an unwanted 60
Hz signal at 1 volt P-P plus a desired signal at 1
mV P-P .If
an attempt is made to display the desired signal with the
VOLTS/DIV switch set to .2
mV,
the
60 Hz signal would
produce a deflection equivalent to
5000 div, and thus little
useful information about the 1 mV signal could
be obtained .
If, however, the same 1
mV signal is monitored differenti-
ally so that the 60 Hz signal is common-mode at the inputs,
no greater than one part in one hundred
thousand of
the
common-mode
signal will appear in the display . Thus, the
desired signal
produces a display amplitude of 5 div with
only .05 div of interference
due to
the
common-mode signal .
There are a
number of factors which can degrade common-
mode
rejection . The principal requirement for maximum re-
jection is for the
common-mode signal to arrive at the input
FET
gates in presicely the same form . A difference of only
0 .01 %
in the attenuation factors of the input attenuators may
reduce the
rejection ratio to 10,000 :1 . Likewise, any difference
in source impedance at the two points in the source under test
will degrade the rejection ratio . Attenuator probes which do
not
have an adjustable resistance may reduce the rejection
ratio to 100 :1 or less .
Outside influences such as electrostatic and magnetic fields
can also degrade the performance, particularly when low
level signals are involved . Electrostatic interference can be
minimized by using shielded signal transporting leads of the
same type to the two inputs, and by twisting the leads to-
gether throughout most of their length .
Care should be taken to minimize the movement of the
signal transporting leads, as any movement of a lead, in the
presence of a magnetic field, will tend to induce a signal into
that lead . Where an interfering magnetic field cannot be
avoided, the pickup loop formed by the two leads should
be minimized by taping or twisting them together throughout
most of their length . Low-frequency measurements can be
similarly protected by using a shielded cable which contains
a twisted pair of conductors .

Fig . 2-8 . Waveforms showing differential rejection of
a common-mode signal . Resultant waveform tc) shows the difference between the two
signals .
DC Offset Operation
By using the DC OFFSET controls, it is possible to use the
Type 7A22 differentially in a slide-back mode, to observe
small signal whose DC potential difference
may be consider-
able . The offset is continuously adjustable from -f-1
V to
---1 V when the VOLTS/DIV switch is in the 101 V to
10
mV
positions . In the 20 mV, 50
mV
and .1
V positions of the
VOLTS/DIV switch, the 1 V offset is effectively multiplied
by
the input attenuator to a range of
-A-10V .
Table 2-1
sum-
marizes the effective
DC
offset voltages
internally available
for all the VOLTS/DIV switch positions . The
table also lists
the input attenuator that is switched into the amplifier circuit
for the
various VOLTS/DIV switch positions .
'CAUTION-- ±500 volts is the maximum allowable
signal voltage
of each input .
Using the DC OFFSET functions :
Set the Type 7A22 controls as follows :
Operating Instructions--Type 7A22
VOLTS/DIV

lo v
VARIABLE (CAL IN)

CAL
POSITION

Midrange
AC-GND-DC GND
(-
.f-
and -- INPUT)
HF ---3 dB POINT

1 MHz
LF
.--3
dB POINT

DC
STEP ATTEN DC BAL

Adjusted for DC balance
step 3 . See Table 2-1 and front panel
color bands .
5 . Set the LF --3 dB POINT selector
to DC OFFSET .
VOLTS/DIV setting
TABLE 2-1
OFFSET RANGE ATTENUATOR in
1 . Position the trace to graticule center (or some other
convenient reference line) using the POSITION control .
2 . Connect a coaxial cable from the signal source to the
--f-INPUT .
10 tkV to 10 mV 1 x
20 mV
to 0 .1 V _
=±
10 V lox
3 . Set the +INPUT AC-GND-DC switch to
DC
and
meas-
._
-
ure the DC level to be offset .
0 .2 V to 1 V
100 V loo x
2 to
_10
V____ .__ .
24
. Set the VOLTS/DIV to the largest deflection factor in
an
V
-4-
1000 V l 000 X
offset range which will encompass the
DC level measured
in