Keithley 194 User manual

Instruction Manual
Model 194
High Speed Voltmeter
01985, Keithley Instruments, Inc.
Instrument Division
Cleveland, Ohio, U.S.A.
Document Number: 194-901-01 Rev. A

SAFETY PRECAUTIONS
The following safety precautions should be observed before using the Model 194.
This instrument is intended for use by qualified personnel who recognize shock hazards and arc famili.lr
with the safety precautions required to avoid possible injury. Read over this manual carefully before operating
the instrument.
Exercise extreme caution when a shock hazard is present at the instrument’s input. The American National
Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 3OV RMS 01
42.4V peak are present. A good safety practice is to expect that a hazardous voltage is present in any unknown
circuit before measurement.
Do not exceed 3OV RMS between input low and earth ground.
Inspect your test leads for possible wear, cracks, or breaks before coachuse.
For maximum safety, do not touch the test leads or the instrument while power is applied to the circuit undrr
test. Turn the power off and discharge all capacitors before connecting or disconnecting the instrument.
Do not touch any object which could provide a current path to the common side of thr circuit under test
or power line (earth) ground. Always make measurements with dry hands while standing on ‘1dry, insulated
surface capable of withstanding the voltage being measured.
Do not exceed the instrument’s maximum allowable input as defined in the specifications and operation
section of this manual.

SPECIFICATIONS
CHANNEL 1
-- ~..l..y.~.I...u..~u
INPUT IMPEDANCE: l.lMt, (I.OMll on 200” range) shunted by
<47pF.
MAXIMUM ALLOWABLE INPUT: 250” peak, 2xlO’V*Hz.
MAXIMUM COMMON MODE VOLTAGE: 30” rms, 42V Peak,
SxlO~“.Hz.
COMMON MODE RE,ECTfON RATIO: >6OdS at dc to IkHz, IkR
unbalance.
DIFFERENTIAL NONLINEARITY: Ih-Bit: 52 LSD. 8 bit: 50.5 LSB.
TEMPERATURE COEFFlClENT (Of’-18T & **^-5o”c,: < -t(O.l Y
applicable accuracy specification)i”C.
DYNAMIC CHARACTERISTICS
16BIT 8 BIT
Minimum SampleRate
10,s (;;ktfz) 1ps (IMHz)
Maximum Sample Rate IS
Sample Rate Resolution lOOX loons
Number of Samples 1 to 32k 1 t” 65k
Sample interval Accuracy
(typical, excluding time base
accuracy, 0.4”s 2ns
SIGNALINOISE RATIO: 5OdB for full range IOOkHz sine input.
SLEW RATE: 13”lps minimum.
SETTLING TIME: 1 gs to 0.1% of final value.
CHANNEL CROSSTALK: <6OdB at SOOkHz.
INPUT CO”PI.ING: Ac, dc, ground.
FREQUENCY RBSPONSE (Filter Off,:
O.ZdB IdlJ 3dB
dc (15Hz) 20kHz dc @Hz) 20OkHz dc (2Hz) 750kt tz
( ) indicates ac coupled performance.
LOW PASS FILTER: 50kHz, 500kHz, single pole.
TRIGGER CHARACTERISTICS
DELAY:
Pm-Trigger: -Zk<n<-1,Mbitmode; -@kc”<-1.8.bitmod
In/ samples are stored prior to triggering.
Past-Trigger: 1<n < 1x 10’. Storage begins “n” samples after tri
gWi”g.
TRIGGER:
SOURCE DESCRlPTlON
Input Signal Slope: + or
Level: Selectable over input voltage
range and resolution.
External: Negative TTL edge.
Front Pane,: Manual pushbutton.
IEEE-488 Interface: 16 programmable trigger modes.
Other Channel: ,nterna,,y generated.
TIMESASE: Internal: IOMHZ *o.o*%.
Extenta,: IOMHZ nominal, Tn..
e.
6.
I
MATH FUNCTIONS
A”ERAGE: ~1%
” = v...,
PEAK TO PEAK: Difference between maximum and minimum v.,,ws
of samples.
PLUS PEAK: Maximum va,w of samples.
MINUS PEAK: Minimum value of samplcs~
II I
z: (V,-TV...,’
STANDARD DE”,AT,ON: s-u II
TRUE ROOT MEAN SQUARE: II
n 2
INTEGRAL: (‘I*“.+%“..,+ ,F, V.) 1,
DIFFERENCE: Channel 1 Channrl 2,
RATIO: Channel 1 / Chnnncl 2.
v,: Voltage of sanlple i,
n: Total number of samples,
i: Locn,ion of individual ssmplc.
t,: Sample intewa,.
ANALOG OUTPUT
MODES 0”TPuTS USED
CRT x, y, z (blanking)
Oscilloscope y, %(trigger)
Slow Plot x, y, z (pen upidown)
Strip Chart y
x OurPUT: O-10” I”,, scale. 2.44mV rfS”I”ti0”.
Y OUTPIJT: 0.,ov full scale, 2.44mV rCSO,“ti”n
z 0”TP”T: 0”. 5v or 15”.
ZOOM MAGNIFICATION: O.,:, to 1O”O:l
PAN: Across entire memory.
REAL TIME (DMA) OUTPUT
FORMAT: Binary, I&bit or S-bit.
RATE: Same as Sample Rate.
CONTROL LINES: End of Sample, Overrun, tligh Byte. I.ow t,yW

1 FRONT PANEL PROGRAMS 1 1 GENERAL
[
0 IEEE ADDRESS: Set IEEE address.
1 SELF TEST: Performs internal RAM and ROM check.
2 DIGITAL CALIBRATION: Executes calibration procedure.
3 CALlBRATlON STORAGE: Stores calibration constants in
NVRAM.
4 x an-PUT FULL SCALE: Sets full scale x output voltage.
5 Y OUTPUT FULL SCALE: sets full scale Y output voltage.
6 Z OUTPUT BLANKING LEVEL: Sets high or law blanking level.
IEEE-488 BUS IMPLEMENTATION
M”LTH.INE COMMANDS: DCL, LLO, SDC, GET, GIL “NT,
“NL, SPE,SPD,MIA, Mm
“NILINE COMMANDS: IFC, REN, EOI, SRQ, ATN.
INTERFACE FIJNCTIONS: SH1, AHI, T6, no, Lb, LEO, Slu, RLI,
PPO, DC1, DTI, CO, El.
PROGRAMMABLE PARAMETERS: Range, Math Functions, Zero,
Delay, Sample Rate, Number of Samples, Trigger, Calibration, Out-
put Format. Self Test, Display, Status, Service Request, Storage,
Filter, Terminator, fnput Coupling, Buffer Size, Channc,, Saw and
Recall Setups, Front l’anel Frograms 1.6, key Sequence, Slope,
Analog Outputs, EOI.
BINARY TRANSFER RATE: 90k bytesisecond.
DISPLAY: Fourteen-digit alphanumeric LED display. Function and
IEEE bus status also displayed.
RANGING: Manual or autoranging.
WARMUP: One hour to rated accuracy.
OPERATING ENVIRONMENT: 0” to 50°C, 0% to 80% relative
humidity up to 35°C.
STORAGE EN”IRONMENT: -25” to 65°C.
POWER: 105.125” or 210.250” (internal switch selectable), 50117.or
6OHz. 12O”A maximum. 90-110” and 180-220” version available
upon request.
CONNECTORS: All Ii0 connectors are BNC except Real Time Out-
put (“B-25, and IEEE-488 connectors.
DIMENSIONS, WEIGHT: 89mm high x 435mm wide x 448mm
deep (3% in. x 17%in. x 17% in.). Net weight 9.Ikg (20 Ibs.), Dual
Channel unit.
ACCESSORIES AVAILABLE:
Model 1938: Fixed Rack Mounting Kit
Model 1939: Slide Rack Mounting Kit
Model 1944: Channel 2
Model 7007-I: Shielded IEEE-488 Cable, Im (3.2 ft.)
Model 7007-Z: Shielded IEEE-488 Cable, 2m (6.5 ft.)
Model 7051.2: BNC Interconnect Cable, 2 ft.
Model 7051-5: BNC lntcrconnect Cable, 5 ft.
Model 7754.3: BNC to Alligator Cable, 3 ft.
Model 7755: 5On Feed-Through Terminator
Model 8573A: IEEE-488 Interface for IBM PC, PC-AT
Model 194 High Speed Voltmeter
Specificafi~ns subject to chrn,qe withuut notice.

Contains an overview of the instrument including
features, unpacking instructions, as well as available
accessories.
SECTION 1
General Information
Includes an overview of front panel controls, rear
panel configuration, and fundamental measurement
procedures. Use this section to get your instrument
up and running as quickly as possible.
SECTION 2
Getting Started
This section contains detailed operating information
for the Model 194, and the Model 1944 A/D Module.
Use this section as a reference on all front panel
operating aspects of the instrument.
SECTION 3
Operation
Contains information on connecting the Model 194
to the IEEE-488 bus and programming the instru-
ment from a computer.
SECTION 4 ~
IEEE-488 Programming
Outlines procedures necessary to verify that the in-
SECTION 5 i
strument is operating within stated specifications.
Performance Verification ~
A complete description of operating principles for
the instrument is located in this section. Analog,
digital, microcomputer, and power supply circuits
are described, as is the IEEE-488 interface.
SECTION 6
Principles of Operation ~
Details maintenance procedures including fuse re-
placement, option installation, line voltage selection,
calibration, and troubleshooting.
SECTION 7
Maintenance
Includes replacement parts information, schematic
diagrams, and component location drawings for the
SECTION 8
Models 194 and 1944.
Replaceable Parts

TABLE OF CONTENTS
SECTION l-GENERAL INFORMATION
1.1 INTRODUCTION ............................................................................. l-l
1.2 FEATURES............................................................................~ ....... i-1
1.3 WARRANTYINFORMATION ................................................................... 1-l
1.4 MANUAL ADDENDA.. ....................................................................... l-2
1.5 SAFETY PRECAUTIONS AND TERMS .......................................................... l-2
1.6 SPECIFICATIONS ............................................................................. l-2
1.6.1 Resolution.. ................................................................................ l-2
1.6.2 Differential Non-Linearity .................................................................... l-2
1.6.3 Slew Rate ................................................................................... ~1-2
1.6.4 Input Impedance and Coupling, .............................................................. l-2
1.6.5 Common-Mode Considerations ............................................................... 1-3
1.6.6 Crosstalk ................................................................................... I-4
1.6.7 DC Voltage Accuracy and Dynamic Characteristics. ............................................. l-4
1.6.8 Settling Time ................................................................................ I-4
1.7 UNPACKING AND INSPECTION .............................................................. l-5
1.8 PREPARATION FOR USE.. .................................................................... ~1-5
1.9 REPACKINGFORSHIPMENT .................................................................. l-5
1.10 ACCESSORIES ................................................................................ l-5
SECTION 2-GETTING STARTED
2.1 INTRODUCTION ............................................................................. 2-l
2.2 FRONT PANEL FAMILIARIZATION ............................................................ 2-l
2.2.1 Controls .................................................................................... 2-1
2.2.2 Display ..................................................................................... 2-8
2.2.3 IEEE-488 Status Indicators .................................................................... 2-Y
2.2.4 TiltBail ..................................................................................... 2-Y
2.3 REAR PANEL FAMILIARIZATION .............................................................. 2-Y
2.4 POWERUPPROCEDURE ..................................................................... 2-12
2.4.1 Power Line Connections ..................................................................... 2-12
2.4.2 Power Up Self Test and Display Messages .................................................... 2-13
2.5 BASIC MEASUREMENT TECHNIQUES ........................................................ 2.14
2.5.1 Warmup Period ............................................................................ 2.14
2.5.2 Input Connections .......................................................................... 2-14
2.5.3 Fundamental Control Selection .............................................................. 2:14
2.5.4 Measurement Procedure ..................................................................... 2.35
2.6 SAMPLES, MEASUREMENTS AND READINGS ................................................ 2.15
2.6.1 Definitions ................................................................................. 2-15
2.6.2 Sampling Discussion ........................................................................ 2-X
2.7 TYPICAL OPERATING MODES ............................................................... 2-16
SECTION 3-OPERATION
3.1 INTRODUCTION ............................................................................. 3;l
3.2 GENERAL DISPLAY MESSAGES ............................................................... 3-2
3.3 RANGE SELECTION .......................................................................... 3-2
3.3.1 Autoranging ................................................................................ 3-2
3.3.2 Uprange .................................................................................... 3-2
3.3.3
Downrange .................................................................................
3-3
3.3.4 Range Selection Considerations. .............................................................. 3-3
3.4 DATA ENTRY ................................................................................. 3-3
3.4.1 DataKeys .................................................................................. 3-3
I

3.4.2
3.4.3
3.4.3
3.4.5
3.4.6
3.5
3.5.1
3.5.2
3.5.3
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.6.6
3.6.7
3.7
3.8
3.9
3.9.3
3.9.2
3.9.3
3.9.4
3.10
3.10.1
3.10.2
3.10.3
3.11
3:12
3.12.1
3.12.2
3.12.3
3.12.4
3.12.5
3.12.6
3.12.7
3.w
3.13.1
3.13.2
3.13.3
3.33.4
3.13.5
3.13.6
3.13.7
3.14
3.14.1
3.14.2
3.15
3.16
3.16.1
3.16.2
3.17
3.18
3.19
3.20
3.20.1
3.20.2
3.20.3
ENTER ..................................................................................... 3.4
CANCEL....................................................; .............................. 3.4
FREQiTIME ................................................................................. 3.4
Using the Cursor Keys ....................................................................... 3.4
Data-Entry Examples ........................................................................ 3.5
RATE AND SAMPLES PROGRAMMING ....................................................... 3-5
Programming Sampling Rate ................................................................. 3-6
Programming the Number of Samples ........................................................ 3-6
Samples and Rate Selection Considerations. ................................................... 3-8
TRIGGERING ................................................................................ 3-9
Trigger Source .............................................................................. 3-10
Single/Continuous Arming Modes ........................................................... 3-10
TRIGGER Button Operation ................................................................. 3-10
Trigger Delay ............................................................................... 3-11
Trigger Slope ............................................................................... 3-13
Trigger Level ............................................................................... 3-W
External Triggering .......................................................................... 3-14
1NPLJT COUPLING ..................................................... .................... 3-14
RECALLING DATA.. ......................................................................... 3-15
DLJALCHANNEI. OPERATION ............................................................... 3-16
Channel 2 Connections ..................................................................... 3-16
Channel Selection .......................................................................... 3.16
Speed Considerations ....................................................................... 3-17
Cross Channel Triggering .................................................................... 3-17
USING ZERO ................................................................................ 3-17
Zeroing From an Applied Signal ............................................................. 3~18
Keying In the Zero Value .................................................................... 3-18
Zero Mode Considerations .................................................................. 3-18
FILTERING .................................................................................. 3-19
USING THE ANALOG OUTPUT .............................................................. 3-21
Analog Output Connections ................................................................. 3.21
Entering the XY Mode (XY MODE) 3-22
Analog Output Data Source (XY DATA) ..................................................... : 3.23
Triggering the Analog Output (XY TRIG). .................................................... 3.24
Scaling the Analog Output (XY ZOOM). ..................................................... 3.24
Controlling the Analog Output Viewed Data (XV PAN) ........................................ 3.25
Setting Maximum Analog Output Levels ..................................................... 3-27
MATHEMATICAL FUNCTIONS ............................................................... 3-29
Average ................................................................................... 3-30
True RMS ................................................................................. 3.30
Peak ...................................................................................... 3.31
Peak-to-Peak ............................................................................... 3-31
Standard Deviation. ........................................................................ 3.32
Integral .................................................................................... 3.32
WaveformMode ............................................................................ 3.33
RATIOANDDIFFERENCE ................................................................... 3.33
DifferenceMode ........................................................................... 3.33
RatioMode ................................................................................ 3.34
STATUS ..................................................................................... 3.34
SETUP MODE ............................................................................... 3-35
RecallinaSetuus ........................................................................... 3.35
Saving SYetups'..............................................
FRONT PANEL PROGRAMS (OTHER KEY OPERATION) ........
RESET .......................................................
EXTERNAL CLOCK ...........................................
REAL TIME OUTPUT .........................................
Signal Lines.. ..............................................
Reading Real Time Data ......................................
Computer Interfacing.. ......................................
.............
.............
.............
.............
.............
.............
......
......
......
......
......
......
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......
......
......
......
......
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3.35
3-36
3-36
3-37
3-38
3-38
3-39
3.40
ii

3.21
3.21.1
3.21.2
3.21.3
321.4
3.21.5
3.22
3.22.1
3.22.2
3.22.3
3.22.4
3.22.5
3.22.6
3.22.7
MEASUREMENT CONSIDERATIONS ...
Ground Loops .......................
RF1 .................................
Instrument Loading Effects. ...........
Input Capacitance Effects ......... ...
AC Frequency Response Considerations
TYPICAL APPLICATIONS ..............
Periodic Waveform Analysis ...........
Long Term Measurements .............
Digital Storage Oscilloscope ...........
Dual-Channel V&meter ..............
Catch a Falling Pulse .................
Reducing Noise in the Measured Signal
Mechanical Vibration Testing ..........
SECTION 4-IEEE-488 PROGRAMMING
4.1
4.2
4.3
4.4
4.5
4.6
4.6.1
4.6.2
4.6.3
4.7
4.7.1
4.7.2
4.7.3
4.8
4.8.1
4.8.2
4.8.3
4.8.4
48.5
4.8.6
4.8.7
4.8.8
4.9
4.9.1
4.9.2
4.9.3
4.9.4
4.9.5
4.9.6
4.9.7
4.9.8
4.9.9
4.9.10
4.9.11
4.9.12
4.9.13
4.9.14
4.9.15
14.9.16
4.9.17
4.9.18
4.9.19
._....
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,.........
,.........
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,....,
......
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......
......
3-43
3-43
3-43
344
3-44
3-45
3-40
3-46
3-47
3.47
3.48
?-4X
3-x
3-5 I
INTRODUCTION ............................................................................. 4-l
A SHORTCUT TO IEEE488 OPERATION .................... ................................. 4-I
BUS CONNECTIONS ......................................................................... 1-3
INTERFACE FUNCTION CODES ....................... ................................... ... J-6
PRIMARY ADDRESS SELECTION .............. ................................... ...... ... 4-h
CONTROLLER PROGRAMMING ........................ ........................ ......... 4-7
LunIrOlier tlanaier sorrware ............................ ................. ...... ...... .. -t-i
BASIC Interface Programming Statements. ............... .......... ...... ...... .......... 4-i
Model 8573 Software Configuration ................ .......... ...... ...... ...... ........ 4-H
FRONT PANEL ASPECTS OF IEEE-488 OPERATION .. .......... ...... ...... ................. 4-8
Front Panel Error Messages
IEEE-488 Status Indicators
............... ....... ........................ 4-N
..................................... .......... 4-10
IX)CALKey.....................................................................~ .......... 4mlU
GENERAL BUS COMMAtiD PROGRAMMING ................ ........................ ...... &lO
REN(Remote Enable) ....................................................................... 4.11
IFC(Interface Clear) ........................................................................ 412
LLO(LocalLockout).............................................................~ .......... 4-12
GTL(GoTo Local) .......................................................................... 4.12
DCL (Device Clear) ......................................................................... 4.13
SDC (Selective Device Clear) ..................................................... ......... 4-14
GET (Group Execute Trigger) .......... .......... ...... .......... ...... ...... ......... 4-14
Serial Polling (SI’E, SPD) .... ..................................................... ......... 4-15
DEVICE-DEPENDENT COMMAND PROGRAI\?MING ...... .......... ...................... 4-15
Execute (X) ....... ........................................................................ 4.20
Function(F) ............................................................................... 4.20
Range(R) .................................................................................. 4-21
Rate(S) ................................................................................... 4.22
Number of Samples(N) .................................................................... 4-22
Trigger Mode (T) ........................................................................... 4-23
Delay(W) ................................................................................. 4-25
Data Format(G) ............................................................................ 4.26
Analog Output(O) ......................................................................... 4-30
BufferPointer Control(B).....................................................~ ............. 4-31
Reading Buffer Control (Q). .......................................................... ...... 4-32
Filter(P) ................................................................................... 4.34
Zero (Z) ................................................................................ .. 4-34
Input Coupling(I) ...................................................................... .. 4-35
status (U) ................................................................................. 4-35
SRQ Mode (M) and Status Byte Format ..................................... ................ 4-40
Channel (C) ............................................................................... 4-43
EOI and Bus Hold-off Modes (K) ............................................................ 444
Terminator (Y) ................................................................ ............ 4-45
iii

4.9.20 Save (L) ......................................................
4.9.21 Recall(A) .....................................................
4.9.22 Hit Button (II) .............. ............ ....................
4.9.23 Display (D) ...................................................
4.9.24 Self Test(J) ...................................................
4.10 TRANSLATOR MODE ............................ ...... ......
4.10.1 Defining Translator Words (ALIAS) .............................
4.10.2 Enabling and Disabling the Translator Mode (KNEW and OLD)
4.10.3 Combining Translator Words ............................ ......
4.10.4 Reading Back Translator Words (LIST). ..........................
4.10.5
Purging Translator Words (FORGET) ............................
4.11 BUS DATA TRANSMISSIOX TIMES. .............................
SECTION 5-PERFORMANCE VERIFICATION
,...,
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......
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......
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.,....
4-46
4-47
4-47
4-48
4-49
4-50
4-50
4-52
4-53
4-53
4-54
4-54
3.1 1NTRODUCTION ............................................................................. 5-l
5.2 ENVIRONMENTALCONDITIONS ............................................................. 5-l
5.3
5.4
5.5
5.6
5.7
5.71
5.72
5.8
INITIAL CONDITIONS
RECOMMENDED TEST EQUIPMENT .................
TEST EQUIPMENT CO1
‘JNECTIONS ...................
VERIFICATION PROCEDI JR1
COMPUTERIZED VERIFICATION ......................
HP-85 Verification Program
IBh? PC/Model 8573 Verification Program
AC FREQUENCY RESPONSE
SECTION 6-PRINCIPLES OF OPERATION
6.1
6.2
6.3
6.3.1
6.3.2
6.4
6.4.1
6.4.2
6.4.3
6.4.4
6.4.5
6.5
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5
6.5.6
6.5.7
6.5.8
6.5.9
6.6
6.6.1
6.6.2
6.6.3
6.6.4
6.6.5
6.6.6
6.6.7
6.6.8
... 5-l
....................................... 5-l
....................................... 5-2
....................................... 5-2
....................................... 5-3
....................................... 5-3
....................................... 5-5
....................................... 5-6
INTRODUCTION ............................................................................. 6-l
FUNCTIONALDESCRIPTION ................................................................. 6-l
ANAU)GCIRCU~RY ......................................................................... 6-3
BlockDiagram .............................................................................. 6-3
Circuit Description .......................................................................... 6-3
A!D CONVERTER ............................................................................ 6-4
Converter Block Diagram .................................................................... 6-4
Converter MDdule ........................................................................... 6-6
FaraIlel-to-Serial Data Conversion ............................................................. 6-8
Data Transmission Control ................................................................... 6-8
Serial Control ............................................................................... 6-8
DIGITAL CONTROL CIRCUITRY. .............................................................. 6-9
Block Diagram of Digital Circ~uitry ...................................................... ..... 6-9
Isolator Data Transmission, ................. ................................................ 6-11
Serial-to-Parallel Data Conversion ... ..............................
Sample Counter ..................................................
Digital Trigger Comparator Circuits. ................................
Trigger Period Control Logic .......................................
64K Byte Dual-Port Memory .......................................
Digital Control-to-Microprocessor Interfacing Circuits ................
Non-Volatile Memory Circuits (NVRAM) ............................
MlCROCOMI’UTER ................................................
Microcomputer Block Diagram .....................................
68008 Microprocessor .............................................
Clock and Reset Circuits ..........................................
Address Decoder .................................................
Control Circuits .......................... .......................
Memory Circuits ..................................................
Buffers ..........................................................
IEEE-488 Interfacing ...............................................
.... ...................
........................
6-12
6-12
6-12
6-13
6-13
6-14
6-N
6-14
6-14
6-16
6-16
6-17
6-U
h-18
6.la
6-E
iv

6.7 I/O (Input/Output) Circuitry. .............................
6.7.1 I/O Block Diagram. ....................................
6.7.2 Bus Buffering ..........................................
6.7.3 Display and Keyboard Interface ..........................
6.7.4 Serial and NVRAM Control .............................
6.75 Analog Output Interfacing ..............................
6.8 POWER SUPPLIES.. .....................................
6.8.1
Power Supply Block Diagram. ...........................
6.8.2 Power LineInput .......................................
6.8.3 Digital Supplies ........................................
6.8.4 Analog Supplies .......................................
6.9 DISPLAYBOARD ........................................
6.9.1 Block Diagram of Display Board .........................
6.9.2 Circuit Description .....................................
SECTION -/-MAINTENANCE
.................
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6-l’)
6.1Y
6-21
h-21
6-21
h-21
6.2~1
b-21
h-22
h-23
h-23
h-21
6-24
h-25
7.1
7.2
7.3
7.3.1
7.3.2
7.4
7.4.1
7.4.2
7.5
ix.1
7.5.2
7.5.3
7.5.4
7.5.5
7.5.6
7.6
7.7
7.7.1
7.7.2
7.7.3
7.7.4
7.7.5
7.8
7.8.1
7.8.2
7.8.3
7.8.4
7.8.5
7.8.6
7.8.7
7.8.8
7.8.9
7.8.10
7.9
7.10
7.11
INTRODUCTION .............................................................................. 7.1
LINE VOLTAGE SELECTION ................................................................... 7-l
FUSE REPLACEMENT ......................................................................... 7-2
Line Fuse Replacement ....................................................................... 7-2
Digital Supply Fuse Replacement ............................................................. 7-2
OPTION INSTALLATION.. .................................................................... 7-2
Installation Procedures ....................................................................... 7.2
Module Recognition Programming ............................................................ 7-6
CALIBRATION ........................................................................... ... 7-h
Recommended Calibration Equipment ......................................................... 7-h
Environmental Conditions, ......................................................... ......... 7-0
Warm-up Period ............................................................................. 7-i
Front Panel Calibration ....................................................................... 7-7
IEEE-488 Bus Calibration ..................................................................... 7-X
Input Amplifier Frequency Compensation Adjustment ......................................... 7-10
SPECIAL HANDLING OR STATIC-SENSITIVE DEVICES ........................................ 7-12
DISASSEMBLY ............................................................................... 7-13
Top and Bottom Cover Removal .............................................................. 7-13
Circuit Board Removal and Replacement ................................................... .. 7-15
Case Disassembly .......................................................................... 7-20
Rear Panel Disassembly ..................................................................... 7-20
Front Panel Disassembly .................................................................... 7-20
TROUBLESHOOTING ........................................................................ 7.25
Recommended Test Equipment .............................................................. 7-2.5
SelfTest ................................................................................... 7-25
Troubleshooting Sequence. .................................................................. 7-27
Power Supply Checks ....................................................................... 7-27
Microcomputer ............................................................................. 7.27
Display Board.. ............................................................................ 7-27
l/O Board .................................................................................. 7-27
Analog Circuitry Checks .................................................................... 7~33
A/D Converter Checks ...................................................................... 7~3.1
A/D Board Digital Circuitry Checks .......................................................... 7-33
FAN FILTER CLEANING/REPLACEMENT ...................................................... 7-38
Z OUTPUT HIGH LEVEL MODIFICATION ................................................. .. 7-38
CIRCUITBOARDJUMPERLOCATIONS ....................................................... 7-38
SECTION 8--REPLACEABLE PARTS
8.1
INTRODUCTION .,,....,...........,...........,,,........................
8.2 ELECTRICAL PARTS LIST ,..........,,,.......,...,.........,,........,....
::::::::::::::::::HH::

8.3 MECHANICAL PARTS ........................................................................ 8-l
8.4 ORDERING INFORMATION.. ................................................................. 8-l
8.5 FACTORY SERVICE ........................................................................... 8-l
8.6 COMPONENT LOCATION DRAWINGS AND SCHEMATIC DIAGRAMS .......................... 8-l
APPENDICES
AI’PENDIXA ......................................................................................... A-l
APPENDIX B ......................................................................................... B-l
APPENDIX C ......................................................................................... C-l
APPENDIX D ........................................................................................ D-l
APPENDIX E.. ....................................................................................... E-l
AI’PENDIX F ......................................................................................... F-l
APPENDIX G-IEEE-488 BUS OVERVIEW .............................................................. G-l
APPENDIX H ........................................................................................ FL-1

LIST OF ILLUSTRATIONS
SECTION l-GENERAL INFORMATION
l-l Equivalent Input Impedance ................................................................... l-2
l-2 Methods of Input Coupling .................................................................... l-3
l-3 Common Mode Voltage.. ...................................................................... ~I-3
l-4 SettlingTime ................................................................................. I-4
SECTION 2-GETTING STARTED
2-l Model194 Front Panel ......................................................................... 2-2
2-2 Front Panel Controls .......................................................................... 2-J
2-3 Front Panel Controls .......................................................................... 2-h
2-4 Display Format ............................................................................... 2-X
2-5 Model194RearPanel ......................................................................... Z-10
2-6 Rear Panel A/D Module Connectors., .......................................................... 2.11
2-7 Rear Panel Connectors, Fuse and Fan .......................................................... 2-12
2-8 Basic Input Connections ...................................................................... 2-15
2-9 Basic Sampling ............................................................................... 2-K
SECTION 3-OPERATION
3-l
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
3-12
3-13
3-14
3-15
3-16
3-17
3-u
3-19
3-20
3-21
3-22
3-23
3-24
3-25
3-26
3-27
3-28
3-29
3-30
3-31
Trigger Delay ................................................................................ 3-12
Level and Slope Triggering .................................................................... 3.13
TRIGGER IN Pulse Specifications .............................................................. 3-14
TRIGGER OUT Pulse Specifications ............................................................ 3-14
Rear Panel Showing Channel 2 Installed ........................................................ 3.16
Typical Filter Response Curves ................................................................ 3.20
Rear Panel Showing ANALOG OUTPUT Jacks .................................................. 3~21
Typical Plotter Connections ................................................................... 3.21
Typical Oscilloscope Connections .............................................................. 3-22
Typical CRT Connections ..................................................................... 3-22
How Scaling Factor Affects Viewed Data ....................................................... 3-25
Moving Analog Output Viewed Data with XY PAN ............................................. 3-26
Output Blanking Levels ....................................................................... 3-28
Integration by Approximate Area Summation. .................................................. 3-33
Synchronous Operation ...................................................................... 3-37
Synchronizing Five Units by Daisy Chaining ................................................... 3-38
Real Time Output Connector. ................................................................. 3-38
Real Time Output Timing ..................................................................... 3-39
Flow Chart for Reading Real Time Data ........................................................ 3-40
Simplified Block Diagram of Real Time Computer Interface ...................................... 3-41
Multiple Ground Points Create a Ground Loop ................................................. 3-43
Eliminating Ground Loop. .................................................................... 3-43
LoadingEffects .............................................................................. 3-44
Input Capacitance Effects ..................................................................... 3-45
Periodic Waveform Analysis
Transient Waveform ............................................................................................................................................. “3%;
Typical Digital Oscilloscope Connections 3-48
DuaIChanneIOperation
Pulse Rwe and Fall Tomes
.....
.............................................................................................................................................................................................
iI+%;
Noise Superimposed on DC Signal ............................................................ 3-50
Vibration Testing ............................................................................. 3-5~1
vii

SECTION 4-IEEE-488 PROGRAMMING
4-l Typical Program Flow Chart ................................................................... 4-2
4-2 IEEE-488 Connector ........................................................................... 4-3
4-3 IEEE-488 Connections ......................................................................... 4-S
4-4 IEEE-488 Connector Location.. ................................................................. 4-5
4-5 Contact Assignments .......................................................................... 4-6
4-6 ASCII Data Format (GO to c-5) ................................................................ 4.27
4-7 Binary Data Formats .......................................................................... 4-28
4-8 Circular Buffer ............................................................................... 4-33
4-9 UO Status Word .............................................................................. 4.37
4.IO LJl Status Word Format ....................................................................... 4.38
4.11 Data (U2) Status Word Format. ................................................................ 4.39
4-12 U3-Ull Status Word Format ................................................................... 4-39
4.13 SRQ Mask and Status Byte Format ............................................................ 4.41
SECTION 5-PERFORMANCE VERIFICATION
5-l DC Verification Connections ................................................................... 5-2
5-2 Flow Chart ................................................................................... 5-2
s-3 AC Verification Connections .................................................................... 5-6
SECTION 8-PRINCIPLES OF OPERATION
64
Simplified Block Diagraln ...................................................................... h-2
6-2 Simplified Block Diagram of Analog Circuitry ................................................... 6-3
6-3 Block Diagram of AID Converter ............................................................... 6-S
6-4 A/D Converter Timing ......................................................................... 6-7
6-5 Digital Control Block Diagram ................................................................. h-10
6-6 Microcomputer Block Diagram ................................................................. h-15
6-7 Memory Map.. .............................................................................. 6.17
h-8 110BlockDiagram ........................................................................... h-20
6-9 Power Supply Block Diagram ................................................................. h-22
6.10 Display Board Block Diagram ................................................................. 6.24
SECTION 7-MAINTENANCE
7-1
7-2
7-3
7-4
7-5
7-6
7-7
7-8
7-9
7-10
7-11
7-12
7-13
7-14
7-15
7-16
7-17
7-18
Line Voltage Switch and Digital Supply Fuse Locations ........................................... 7-4
Model 1944 A/D Module Installation ............................................................ 7-5
Calibration Procedure Flow Chart. .............................................................. 7-8
Calibration Connections ........................................................................ 7-S
Frequency Compensation Adjustment Locations ................................................. 7.11
AC Frequency Response Calibration Connections ................................................ 7.12
Top and Bottom Cover Removal ................................................................ 7.14
Circuit BoardRemoval ........................................................................ 7-17
Cable Connections ............................................................................ 7-19
Case Assembly ............................................................................... 7.21
Rear Panel Disassembly ....................................................................... 7-23
Front Panel Disassembly ...................................................................... 7-24
Ul Status Word Format ....................................................................... 7-26
Troubleshooting Flow Chart ................................................................... 7-28
Troubleshooting Block Diagram ................................................................ 7-29
Fan Filter Removal ............................................................................ 7-39
Z Output Blanking Level Programming. ........................................................ 7-39
MovableJumper Locations .................................................................... 7.40

SECTION 843EPLACEABLE PARTS
8-l MechanicalPartsLocation ...................................................................... 8-3
8-2 Mother Board, Component Location Drawing, Dwg. No. 194-100. ................................. S-10
8-3 Mother Board, Schematic Diagram, Dwg. No. 194-106. ........................................... 8-11
8-4 Display Board, Component Location Drawing, Dwg. No. 194-110 ................................. 8-20
8-5 Display Board, Schematic Diagram, Dwg. No. 194-116 ........................................... 8-21
8-6 A/D Board, Component Location Drawing, Dwg. No. 194.120 .................................... 8-30
8-7 A/D Board, Schematic Diagram, Dwg. No. 194-126 .............................................. 8-31
8-8 I/O Board, Component Location Drawing, Dwg. No. 194-160 ..................................... 8-42
8-9 I/O Board, Schematic Diagram, Dwg. No. 194-166 ............................................... 8-43
8-10 Sample Rate Board, Component Location Drawing, Dwg. No. 194-170. ............................ 8-45
8.11 Sample Rate Board Schematic Diagram, Dwg. No. 194.176 ....................................... 8-46
APPENDIX G
G-l IEEE Bus Configuration ....................................................................... G-l
G-2 IEEE Handshake Sequence .................................................................... CT-3
G-3 Command Codes ............................................................................. Gh
ix

LIST OF TABLES
SECTION 2-GETTING STARTED
24
Front Panel Control Summary .................................................................. 2-3
2-2 Limits and Resolution for Programmable Parameters. ............................................. 2-7
2-3 Rear Panel Summary .......................................................................... 2-9
2-4 Factory Default Power Up Conditions .......................................................... 2.13
2-s Recommended Operating Modes For Typical Waveforms ......................................... 2-17
SECTION 3-OPERATION
3-l General Display Messages ..................................................................... 3-2
3-2 Range Summary.. ............................................................................ 3-2
3-3 Trigger Source Display Messages ............................................................... 3-10
3-4 Display Format ............................................................................... 3.17
3-5 Filter Display Messages ....................................................................... 3.19
3-6 Filter Response Times ......................................................................... 3.19
3-7 XY Mode Display Messages ................................................................... 3-22
3-8 XY Mode Level Programming ................................................................. 3.27
3-Y Math Function Display Messages .............................................................. 3.29
3.10 Data For Mathematical Function Examples. ..................................................... 3-31
3-11 Ratio and Difference Display Messages ......................................................... 3-33
3.12 Typical Status Mode Display Messages ......................................................... 3.35
3-13 Setup Mode Display Messages ................................................................ 3.35
3-14 Front Panel rrograms ......................................................................... 3-36
3-15 Factory Default (RESET (SETUP 1) Conditions .................................................. 3.37
3-16 Synchronizing Five Units by Daisy Chaining ................................................... 3-38
3-17 Voltage and Percent Error For Various Time Constants ........................................... 3.45
SECTION 4-IEEE-488 PROGRAMMING
4-l
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4.11
4.12
4-13
4-14
4-15
4-16
4-17
4-18
4-19
4-20
4-21
4-22
4-23
4-24
x
Summary of Most Often Used IEEE-488 Commands ............................................. 4-4
IEEE Contact Designations ..................................................................... 4-5
Model 194 Interface Function Codes ............................................................ 4-6
BASIC Statements Necessary to Send Bus Commands ............................................ 4-8
Front PanelIEEE-488 Messages ................................................................. 4-8
General Bus Commands and Associated BASIC Statements ...................................... 4-11
Power on, DCL, or SDC Default Conditions .................................................... 4-13
Device-Dependent Command Summary ........................................................ 4-17
Function Commands ......................................................................... 4-21
RangeCommands ............................................................................ 4-21
Rate Commands ............................................................................. 4-22
Number of Samples Commands ............................................................... 4.22
Trigger Commands ........................................................................... 4.23
Delay Commands ............................................................................ 4.25
Data Format Commands ...................................................................... 4.26
Buffer Pointer Select Commands. .............................................................. 4.31
Reading Buffer Control Commands ............................................................ 4.32
Filter Commands ............................................................................ 4.34
Zero Mode Commands.. ..................................................................... 4.34
Input Coupling Commands ................................................................... 4.35
Status Commands ........................................................................... 4-36
Values Returned to UO Status for Last Button Pressed ........................................... 4-36
SRQ Commands ............................................................................. 4.41
Channel Control Commands .................................................................. 4-43

4-25 EOI and Bus Hold-Off Commands ............
4-26 Typical NRFD Hold-Off Times ................
4-27 Terminator Commands .......................
4-28 Save Command Summary ....................
4-29 Modes Stored By Save Command .............
4-30 Recall Commands ............................
4-31 Hit Commands ..............................
4-32 Display Commands ..........................
4-33 UO Self Test Error Codes ......................
4-34 Translator Reserved Words and Character ......
4-35 Bus Data Transmission Times .................
SECTION 5-PERFORMANCE VERIFICATION
......
......
......
......
......
......
......
......
......
......
5-l Performance Verification Equipment. ......................... 5-1
5-2 Performance Verification Limits ............................... 5.3
5-3 AC Frequency Response Verification .......................... .%6
SECTION 8-PRINCIPLES OF OPERATION
6-l Attenuator and Gain Values. .......................
6-2 Memory Mapping ................................
SECTION 7-MAINTENANCE
......
......
......
......
......
.....
......
......
......
......
......
...... ....... 4-44
....... 4-45
....... 4-45
....... 4-46
....... 4-46
....... 4-47
... 4-4x
... 4-48
... 4.49
....... 4-M
....... 4.ss
h-4
h-17
7-l
7-2
7-3
7-4
7-s
7-6
7-7
7-8
7-9
7-10
7-11
F-12
7-13
7-14
7-15
7-16
7-17
Line Voltage Selection .................................................................... .... 7-2
Line Fuse Selection ....................................................................... .... 7-2
Recommended Calibration Equipment ........................................................... 7-7
Calibration Surnmary .......................................................................... 7-7
AC Response Adjustment Procedure.
Static Sensltwe Dewces .. ............................................................................................................... 7.10
................. 7-L?
Recommended Troubleshooting Equipment ..................................................... 7-25
Self Test Display Messages .................................................................... 7-25
Power Supply Checks ........................................................................ 7-30
MicrocomputerChecks ........................................................................ 7.31
Display Board Checks ........................................................................ 7-31
I/O BoardChecks ............................................................................ 7-32
Input Amplifier Checks
Input Amplifier Gain Values
.................................................................................................................................................................................................................
7-34
7-34
A/D Converter Checks 7-35
A/D Module Digital Circuitry Checks .......................................................... 7-37
Z Output Resistor Values ..................................................................... 7-38
SECTION 8-REPLACEABLE PARTS
8-l Mother Board, Parts List ..........................
8-2 Display Board, Parts List .........................
8-3 A/D Board, Parts List, ............................
8-4 I/O Board, Parts List .............................
8-5 Sample Rate Board, Parts List .....................
8-6 Case Assembly, Parts List .........................
8-7 Miscellaneous Mechanical, Parts List. ..............
............................ ........
............................
............................
............................
,.....
......
......
........ R-6
........ 8-18
....... 8-24
....... 8.40
... 8-45
....... 8-47
....... 8-48
xi

APPENDICES
G-l
G-2
G-3
G-4
G-S
............................................................
IEEE-488 Bus Command Summary. G-3
Hexadecimal and Decimal Command Codes .................................................... G-7
Typical Addressed Command Sequence ........................................................ G-7
................................................. G-7
Typical Device-Dependent Command Sequence
IEEE Command Group ........................................................................ G-7
xii

SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
This section contains information on Model 194features,
warranty, manual addenda, safety terms and symbols, and
specifications. Also included are procedures for unpack-
ing and inspecting the instrument, as well as available
accessories.
The information in Section 1 is divided into the following
major paragraphs:
1.2 Features
1.3 Warranty Information
1.4 Manual Addenda
1.5 Safety Symbols and Terms
1.6 Specifications
1.7 Unpacking and Inspection
1.9 Preparation For Use
1.9 Repacking For Shipment
1.10 Accessories
1.2 FEATURES
The Model 194High Speed Voltmeter is a high speed DC
voltage sampling instrument suitable for a wide variety of
applications, including the analysis of laboratory
phenomenon, as well as the characterization of transient
and periodic waveforms.
The Model 194 can sample at rates up to lMHr with 2%
digit, a-bit usable resolution, or up to 1OOkHz with 4%
digit, 16-bit resolution. Each A/D channel has 64K bytes
of memory allowing up to 65,535 samples to be stored for
later analysis with one of the many Model 194mathematical
functions.
Key Model 194 features include:
l Autoranging-Autoranging allows the instrument to
measure a wide dynamic range of input signals.
l Zero-A zero feature allows a baseline signal level to be
subtracted from subsequent readings. The baseline can
either be taken from a” applied signal, or keyed in from
the front panel or programmed over the IEEE-488 bus.
l Filtering-Internal analog filtering with sclcctablc poles
of 50kHz or 500kHz is available to reduce the effects of
noise.
l Math Functions-A number of mathematical functions
including average, integral, standard deviation, true
RMS, peak, and peak-to-peak arc included with the in-
strument software.
l Dual-channel Operation-Two separate, isolated AID
channels are available with the optional Model 1944AiD
Module installed.
l IEEE-488 Interface-A standard feature of the Model 194
that allows the instrument to be controlled from rl
computer.
l Real Time Output-This port allows instrument data to
be transmitted to a computer or similar device at the
sampling rate via a user-supplied interface.
l Programmable Sampling Rates-The instrument CA” bc
programmed to sample data as fast as ‘IMHz, or as slw
as 1Hz.
l Programmable Number of Samples-The number oi sam
pies per measurement sequence Cd” bc prw
grammed to any value between I and 32,767 (~16.bitrc’so-
lution) or 1 and 65,535 (X-bit resolution).
l I’rogramtnable Triggering-The instrument ca” bc trig-
gered from the input signal, an external triger signal,
from the other channel (when the Model 1944option is
installed), or over the IEEE-488 bus. Programmable trig-
gering parameters include single or continuous modes,
delay, slope, and level.
l XY Mode-Allows the instrument to drive external
display devices such as oscilloscopes and plotters. Inter-
nal software allows easy generation of graphs from
sampled data.
l Translator Mode-Simplifies IEEE-488 programming by
allowing the use of English-like syntax.
1.3 WARRANTY INFORMATION
Warranty information for your Model 194 may be found
inside the front cover of this manual. Should it become
necessary to use the warranty, contact your Keithley
representative or the factory for inform&&xl 011obtaining
warranty service. Keithley Instruments, Inc. maintains ser-
vice facilities in the United States, West Germany, France,
the Netherlands, Switzerland, and Australia. Information
concerning the operation, application, or service of the
Model 194 may be obtained by contacting an applications
engineer at any of these locations.
l-l

GENERAL INFOHMATION
1.4 MANUAL ADDENDA
Information concerning improvements or changes to the
instrument which occur after this manual is printed will
be found on an addendum sheet included with the instru-
ment. Please be sure that you read this information before
attempting to operate or service your instrument.
1.5 SAFETY SYMBOLS AND TERMS
The following safety terms and symbols are used in this
manual or found on the instrument.
The A symbol on the instrument indicates that the user
should refer to the operating instructions in this manual
for further details.
The WARNING heading as used in this manual explains
dangers that could result in personal injury or death.
Always read the associated information very carefully
before performing the indicated procedure.
The CAUTION heading used in this manual explains
hazards that could damage the instrument. Such damage
may invalidate the warranty.
1.6 SPECIFICATIONS
Detailed Model 194 specifications are located at the front
of this manual. Some terms used in the specifications are
discussed in the following paragraphs.
1.6.1 Resolution
The resolution of an A/D converter is generally defined
as the number of output states expressed in bits. The
number of output states of a binary quantizing A/D con-
verter is Zn, where n represents the number of bits. The
AID converter in the Model 394 operates with either a-bit
or 16.bit resolution, depending on the sampling rate. Thus,
the AID converter has either 256 (28)or 65,536 (216)output
states.
The resolution figures given in the specifications are de-
rived by dividing the full scale displayable range by the
number of steps for that particular converter resolution.
For example, in the lh-bit mode, the 32OmV range is ac-
tually capable of displaying values in the range of -327.68
to + 32.7.67mV,for a total range of 655.35mV. Dividing this
figure by the total number of quantized steps (65,535)
yields the 1OpVresolution figure given in the specifications.
1.6.2 Differential Non-Linearity
The differential non-linearity specification defines the max-
imum deviation of a quantized step width from the ideal
quantization step width, FSRI(Z”-l), where FSR is the full
scale range of the A/D converter (1OV)and n is the number
of bits (8 or 16) depending on the sampling rate.
1.6.3 Slew Rate
The slew rate specification applies to the sample and hold
portion of the A/D converter and is usually defined as the
maximum rate at which a capacitor can charge expressed
in volts per microsecond. Generally, it is desirable to have
as high a slew rate as possible in order to minimize
response time.
1.6.4 Input Impedance and Coupling
The input impedance is simply the equivalent resistance
appearing between input high and input low shunted by
(in parallel with) the stated capacitance value. Figure 1-l
shows an equivalent circuit of the input impedance appear-
ing at the VOLTAGE INPUT jack. Input impedance can
become especially important when measuring voltage
sources with high internal resistance: the resistive com-
ponent can load the source, degrading measurement ac-
curacy, and the capacitive element can increase response
time to rapidly-changing signals
Figure l-l. Equivalent Input Impedance
I-2

GENERAL INFORMATION
Input coupling defines the method used to apply the signal
1.6.5 Common-Mode Considerations
voltage to the input amplifier. Figure l-2 demonstrates the
three forms of coupling used: AC, DC, and ground. With
the DC coupling method in (a), a straight-through path The low input terminal of the Model 194 can be floated
is established. Figure 1-2(b) shows the AC coupling up to 30V RMS, 42.4V peak above chassis ground. This
method, in which a capacitor is inserted in series with the voltage is known as the common mode voltage and is
high input signal path. In the case of ground coupling shown on the diagram in Figure l-3. The advantage of
[Figure 1-2(c)], the input signal is effectively removed from floating the input is that you can measure many sources
the input terminals of the input amplifier by shorting the that are not referenced to power line ground. The 30V RMS
high and low terminals of the input amplifier together. limitation given in the specifications is defined by ANSI
safety standards; since the shield of any cable connected
to the instrument will also be at common mode potential,
it is imnortant that the 30V limitation be observed to avoid
Figure 1-2. Methods of Input Coupling
a possjble shock hazard
The common mode rejection ratio (CMRR) defines how
much of a common mode signal in the specified frequen-
cy range will appear in the final reading, exclusive of other
factors such as selected math function. Note that this
specification is given is dB and can be converted to an
equivalent noise voltage as follows:
where: V, is the resulting noise voltage.
V,, is the common mode voltage.
CMRR is the common mode rejection ratio in dB.
1-3