AMPLITUDE CALIBRATOR FOR OSCILLOSCOPES

James R. Andrews

Eugene E. Baldwin

Electromagnetic Technology Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

100

.U56

81-1646 April 1981

1981

1c. 2

NBSIR 81-1646

'

NATIONAL BUilSAlJ Or STANDARDS

LIBRARY

JUN 1 5 1981

AMPLITUDE CALIBRATOR FOR OSCILLOSCOPES

Clc/c>o

no. S

7 /- !L

James R. Andrews

Eugene E. Baldwin

Electromagnetic Technology Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

April 1981

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CONTENTS

Page

Abstract 1

1. Introduction 1

2. Specifications and Features 2

3. Circuit Description and Schematics 2

4. Parts List 10

5. Construction 15

6. Alignment Procedure 21

7. Performance Check and Calibration 23

DISCLAIMER: Certain commercial equipment, instruments, or materials are identified in order to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

iii
List of Figures

Page

Figure 1. NBS amplitude calibrator 1 Figure 2. Block diagram of amplitude calibrator 5 Figure 3. Schematic (1 of A) 6 Figure 4. Schematic (2 of 4) 7 Figure 5. Schematic (3 of 4) 8 Figure 6. Schematic (4 of 4) 9 Figure 7. Photo of assembled instrument (cover plates removed) 16 Figure 8. Rear view. (Partially disassembled) 16 Figure 9. P.C. Board #1 17 Figure 10. P.C. Board #2 17 Figure 11. P.C. Board #3 17 Figure 12. P.C. Board #1 art work 18 Figure 13. P.C. Board #2 art work 19 Figure 14. P.C. Board #3 art work 20

iv
AMPLITUDE CALIBRATOR FOR OSCILLOSCOPES

James R. Andrews and Eugene E. Baldwin

National Bureau of Standards

Boulder, Colorado 80303

The amplitude calibrator is designed to provide known dc voltage levels or 1 kHz square waves from + 1 mV to + 5 V, It features selectable output impedances of < 0.1 (2, 50 (2, and 1 M(2. The instrument is designed with sufficient current capability to deliver its indicated voltage into a 50 *1 termination. To protect delicate sampling

oscilloscopes, a limiter circuit can also be activated to limit the output voltage

to + 1.8 V.

Key words: Calibration; calibrators; instrumentation; oscilloscope calibrator; oscilloscopes

1. Introduction

This report describes equipment developed by NBS for calibration of the vertical axis of an oscilloscope. The amplitude calibrator (fig. 1) provides voltages from + 1 mV to + 5 V with AV steps of

1 mV to 500 mV in a 1, 2, 5 sequence and a 0 to 10 multiplier in unit steps with a source impedance of

< 0.1(2, 50(2, or 1 M (2 . It produces either dc or a 1 kHz square wave. This report describes in detail the circuit design. Schematic diagrams, parts list, and p.c. art- work are included. A complete alignment and calibration procedure is provided.

multiplier

SAMPLER

PROTECTION

MODEL 72404-2

S/N- I

N tj S> AMPLITUDE CALIBRATOR

A V IN MILLIVOLTS

OVERLOAD OUTPUT

Figure 1. NBS amplitude calibrator.

1
2. Specifications and Features

NBS Amplitude Calibrator Model - 72404-2

I. Output voltages:

a. + 1 mV to + 5 V

b. AV steps - 1 mV to 500 mV in a 1, 2, 5 sequence.

c. multiplier - 0 to 10 in unit steps.

d. open circuit output voltage is 2X the indicated value when the output impedance switch is in

the 50 £2 or 1 M £2 positions.

II. Voltage accuracy: within + 0.25% (typically < 0.1%) except + 0.4% at 2 mV and + 0.7% at 1 mV.

III. Output impedance: adjustable with 3 position switch to (a) < 0.1 £2, (b) 50 £2, + 0.1% and

(c) 1.0 M £2, + 0.1%.

IV. Operating modes: (a) DC or (b) 1 kHz square wave. Square wave baseline is 0 volts. Frequency

accuracy is + 0.01%.

V. Sampler protection: switch selectable internal circuit limits output voltage to a maximum of

+ 1.8 volts nominal.

VI. Overload protection: overload lamp lights if output current exceeds + 225 mA, nominal, and the

maximum output current is limited to + 275 mA. The lamp also lights if the multiplier and AV

switches would create an output in excess of + 1.2 volts when the sampler protection circuit is

on. VII. Output connector: BNC VIII. Controls: (a) AV in mV, (b) multiplier, (c) polarity (+ or -) , (d) mode (dc or 1 kHz), (e) sampler

protection (on or off) and (f) output impedance.

IX. Construction: the unit is a double-wide, plug-in module designed to be operated in a Tektronix

TM-500 mainframe.

3 . Circuit Description and Schematics

The block diagram of the amplitude calibrator is shown in figure 2. Detailed schematic diagrams

are found in figures 3 through 7. The internal voltage standard for the unit is + 10.000 V found at TP7. An LM399H, IC-10, is used

as a precision voltage reference. It is a temperature stabilized, active reference zener. It features

a typical temperature coefficient of 0.00003%/°C (0.0002%/°C max.). The actual reference voltage is a nominal 6.95 V (+ 0.35 V). The + 10.000 V internal standard voltage is obtained from the 6.95 V reference using the IC-1 and the resistors R , II , and R . The reference voltage is very stable with

a b c time and temperature but it is not well known (i.e., large variation in actual voltage from one unit to the next.) Thus it is necessary to provide a means of varying the gain of IC-1 to accurately

set the internal standard at precisely —+ 10.000 V. Resistor R is used for this function.

c Switch SI provides the polarity function by alternately grounding either the positive or negative

terminal of the 6.95 V reference. The 1 kHz square wave function is obtained using the integrated

analog switch, IC-4. It grounds at a 1 kHz rate the center point of resistors R^ and R^, thus forcing the input to IC-1 to zero. As a result the voltage at TP7 switches from + 10.000 V to 0.00 V. The AV function (1 mV to 500 mV in a 1-2-5 sequence) is provided by the variable gain amplifier

used as an active attenuator IC-2. The gain of this stage is set by the input and feedback resistor ratio

V(TP8) = V (TP7) X R /R.

.

e d

2
Resistors R

g and are precision, 0.1%, resistors and are switched by a common switch to give TP8

voltages ranging from +10 mV to +5.000 V. Following IC-2 is the multiplier attenuator, R^ . This is a passive voltage divider made up of

ten, 1 kfl, 0.1% resistors. This provides the unit step multiplier function (0, 1, 2, etc.

up to 10) . To avoid upsetting the accuracy of R^ it is followed by a very high input impedance voltage

follower, IC-3. Also following the multiplier attenuator is the sampler protection circuit. Most sampling

oscilloscopes have a dynamic range of + 1 V and burnout limits of + 3 V. Thus the maximum output from

this amplitude calibrator could easily destroy a sampling oscilloscope input circuit. To protect

against this a limiter circuit can be switched in to limit the output voltage to a nominal + 1.5 V. The next circuit is a hybrid power amplifier consisting of IC-3 and complementary NPN-PNP Darlington amplifier pairs. This power amplifier is capable of delivering up to + 10 V at 200 mA. The voltage

gain of this stage is unity. The circuit includes short circuit protection.

Beyond the power amplifier is an additional switch to determine the output impedance. The output

impedance of the power amplifier is typically 0.1 fi. Higher impedances are obtained by inserting a series 50 Q or 1 M C resistor. The output voltage in the 50 fi and 1 M position is calibrated in terms of the voltage delivered to a load resistance matched to the source resistance. Thus it is necessary to double the open circuit source voltage. For example when the AV is 500 mV, the multiplier

is 10 and the Z Out is 50 1) or 1 M Q, then the open circuit output voltage is + 10.000 V instead of + 5.000 V. This is accomplished by an additional switch section of the Z Out switch changing resistor

R, in the AV active attenuator,

d

The calibrator also includes an overload lamp. It lights whenever there is an overload or fault condition such as a short circuit on the output. It also lights if the sampler protection circuit is enabled and an output voltage is selected which exceeds the limiter voltage. The remainder of this

section deals with particular comments related to the actual circuits.

In the + 10 V standard circuit, IC-1, in figure 3, the resistors R^ and R^ and the switch IC-4 are actually five resistors and four CMOS switches. Each CMOS switch has a finite on resistance of the order of 100 fi. A single section switch will not give a perfect 0 V input to IC-1. It was necessary

to use multiple sections as a ladder attenuator to achieve the desired accuracy.

The 1 kHz square wave drive signal for IC-4 is derived from a 1 MHz crystal oscillator, IC-5a, and three t 10 dividers, IC-6, 7 and 8. IC-9 is an additional tlO which provides a 100 Hz drive signal for the external, companion, plug-in, mercury switch pulse generator.

The active AV attenuator, IC-2, is seen to have nine (R33-R41) additional resistors in the + input.

These are chosen to approximate the parallel combination of Rd and Re to provide offset current compensation for IC-2. Likewise the extra resistors (R54-R65) in the multiplier attenuator, figure 4, provide

the same function for IC-3 in conjunction with R66. The sampler protection limiter consists of diodes CR1 and 2 and transistors Q1-Q4. The forward

diode drops of CR1, Q1 and Q2 in series provide the equivalent of a + 1.5 V clamp. Diode CR2 , Q3

and Q4 provide the same function for negative voltages. The transitors are connected as high 8 Darlington amplifiers. When they start to conduct they turn on Q14 which in turn lights the overload lamp.

3
The power amplifier is also shown in figure 4. IC-3 provides a high impedance load for the multiplier attenuator and also drives the output power transistors, Q5-Q8. To avoid "cross-over" distortion and non-linearities at low output levels the bias is arranged such that the output

transistors are always conducting. The bias network is made up of diodes CR3-CR6 and resistors R69,

70, 71, 73, and R5 . The diodes provide temperature compensation for the temperature characteristic

of the transistors' base-emitter junction voltage. The JFET transistors Q15a and b are used as constant current sources to force the output transistors to always conduct a few mA of current. The actual

idling current can be adjusted with R5 . The actual output current is monitored by sensing the voltage

drop across the 3.3 £2 resistors, R72 and R74. If the current exceeds 250 mA, then the voltage drop is sufficient to turn on transistor Q9 (or Q10) which in turn kills the base drive at Q5 (or Q7) and very effectively limits the output current. At a slightly lower current of 225 mA, Qll (or Q12) starts to conduct which in turn turns on Q13 and Q14 thereby lighting the overload lamp.

Each op-amp in the calibrator is equipped with a null adjustment pot. It is quite important,

especially for the mV output levels, that each op-amp be precisely nulled to 0 V. To facilitate

these adjustments, slide switches have been provided on the circuit boards.

It is important that the spurious noise output of this calibrator be kept to an absolute minimum.

The major internal source of EMI is the 1 MHz crystal oscillator and the divider chain. To insure a quiet output signal, line filters consisting of C12, C13, C16, C19, R65 and C20 are used. The power

supply lines on each card are filtered with tantalum and ceramic capacitors and RF chokes are used in the wiring between cards. In addition RC filters are used in the V+ and V- lines for each op-amp. Figure 5 shows the wiring between the various pc cards and the front panel controls. Figure 6 shows the power supply card. Main dc power is derived from the TM-500 main-frame through the plug-in

connector. The + 33.5 V supply is pre-regulated to + 20 V using CR9, CR11, Q16, Q18 and power transistors in the main-frame. Integrated circuit voltage regulators, IC11 and 12, are then used to obtain

the required + 15 V. These voltages are further dropped to + 7.5 V for the CMOS ICs using CR10, CR12,

Q17 and Q19.

4
TP7

TP

8

(T>0“

CUH

*V^\W I

1

' +i

o

/ + \

r |

1

i 1

/ +\

.1 i

!

»-o

pH O” H

+

<1 * vW 1

0> u o

P p

P- P

4-» T3 P 0) O PhG

P

0) P *H

QJ 4-4 £ *H O rH

cp a

I

p

Q4

I—

1

p

o

•H

P- a

e cu P -u CO op

p.

p p

QJ O

•H 4-1 rH P

Ph P

•H P

4J a) P 4-1 s <

> • nd O 4J rH CO +

Q)> r£ P u ^ 4-)

cr c/3 co

p

P

i—

i

o

pp

0)u

60 CD p P

4-» Q) rH 4-4 O 0) > &

5

Figure

2.

Block

diagram

of

amplitude

calibrator.
6

Figure

3.

Schematic

(1

of

4)
7

Figure

4.

Schematic

(2

of

4)
8

FRoajt

VA/JELswrrcw

wrRrv^

t>irA

<s,r/)m
id-L O

oeo

i a.

'fc V-"* *- <5-

^ bo o *

so' u- . Sr

'o ^

fOu " W < G> a a ^

V V V V

<r io e> ^

In y. W

«y <v

3^

tl < ^

a- «n -w

* *

P

>

%> CO*

\

<o3

ro

QC

U

«>

~x>*

PC

*1 «Q *3

9

Figure

6.

Schematic

(4

of

4)
4. Parts List

Part Number Description

Value

Card 3

R1 Resistor, trimmer, 10 turn 10 k£2 R2 Resistor, trimmer, 10 turn 20 k£2 R3 Resistor

,

trimmer, 10 turn 20 k£2 RIO Resistor

,

composition 1/4W, 5% 2 k£2 Rll Resistor

,

composition 1/4W, 5% 2 kfi R12 Resistor

,

metal film. 1/8W, 1% 10 kft R13 Resistor, metal film. 1/8W, 1% 10 kfi R14 Resistor, metal film. 1/8W, 1% 10 k£2 R15 Resistor

,

metal film. 1/8W, 1% 10 k£2 R16 Resistor

,

metal film. 1/8W, 1% 33.3 k£2 R17 Resistor

,

metal film, 1/8W, 1% 43.2 kn

R18 Resistor, metal film. 1/8W, 1% 100 k£2 R19 Resistor, composition 1/4W, 5% 100 n R20 Resistor, composition 1/4W, 5% 100 £2 R21 Resistor

,

composition , 1/4W, 5% 10 MEG n R22 Resistor

,

precision. 1/2W, 0.1% 100 kfi R23 Resistor, precision. 1/2W, 0.1% 100 k£2 R24 Resistor

,

precision, 1/2W, 0.1% 10 kfi R25 Resistor, precision. 1/2W, 0.1% 10 k£2 R26 Resistor, precision, 1/2W, 0.1% 10 k£2 R27 Resistor

,

precision, 1/2W, 0.1% 2 k£2 R28 Resistor, precision, 1/2W, 0.1% 2 kfi R29 Resistor

,

precision, 1/2W, 0.1% 1 k£2 R30 Resistor

,

precision. 1/2W, 0.1% 100 £2 R31 Resistor, precision. 1/2W, 0.1% 200 a R32 Resistor, precision, 1/2W, 0.1% 200 n R33 Resistor

,

metal film, 1/8W, 1% 200 £2 R34 Resistor, metal film. 1/8W, 1% 402 £2 R35 Resistor

,

metal film. 1/8W, 1% 100 £2 R36 Resistor, metal film. 1/8W, 1% 196 £2

R37 Resistor, metal film. 1/8W, 1% 383 £2 R38 Resistor, metal film, 1/8W, 1% 909 £2 R39 Resistor, metal film. 1/8W, 1% 1.65 k£2 R40 Resistor, metal film. 1/8W, 1% 2.87 k£2 R41 Resistor, metal film. 1/8W, 1% 4.99 k£2 R42 Resistor, composition , 1/4W, 5% 100 £2 R43 Resistor

,

composition , 1/4W, 5% 100 £2 R100 Resistor, composition , 1/4W, 5% 1M £2

10
Part Number Description Value

Card 3

Cl Capacitor, trimmer 5.5-18 pF

C2 Capacitor, silver mica 33 pF

C3 Capacitor, silver mica 33 pF

C4 Capacitor, tantalum 4.7 pF, 25 V

C5 Capacitor, disc ceramic 0.01 pF, 50 V

C6 Capacitor, disc ceramic 0.01 pF, 50 V

C7 Capacitor, tantalum 4.7 pF, 25 V

C8 Capacitor, tantalum 4.7 pF, 50 V

C9 Capacitor, disc ceramic 0.01 pF, 50 V CIO Capacitor, tantalum 4.7 pF, 25 V Cll Capacitor, disc ceramic 0.01 pF, 50 V

C12 Capacitor, silver mica 120 pF

C13 Capacitor, silver mica 39 pF

C14 Capacitor, plastic 0.01 pF, 100 V C15 Omitted

C16 Omitted

C17 Capacitor, plastic 0.1 pF, 100 V

C18 Capacitor, plastic 0.1 pF, 100 V

Y1 Crystal, 1.0 MHz., .001%

IC1 Operational amplifier 0P-05C

1C2 Operational amplifier OP-05C

IC4 Integrated circuit, CMOS CD4066A

IC5 Integrated circuit, CMOS CD4001AE

IC6 Integrated circuit, CMOS CD4017E

IC7 Integrated circuit, CMOS CD4017E

IC8 Integrated circuit, CMOS CD4017E

IC9 Integrated circuit, CMOS CD4017E

IC10 Integrated circuit, voltage reference LM-399H

S5 Switch, slide, miniature 1 pole, 2 position

S6 Switch, slide, miniature 1 pole, 2 position

S7 Switch, slide, miniature 1 pole, 2 position

11
Part Number Description Value

Card 2

R44 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R45 Resistor, Precision, 1/2 W. , 0.1% 1 kft R46 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R47 Resistor, Precision, 1/2 W., 0.1% 1 kft R48 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R49 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R50 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R51 Resistor

,

Precision, 1/2 W., 0.1% 1 kft R52 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R53 Resistor

,

Precision, 1/2 W. , 0.1% 1 kft R54 Resistor

,

Metal Film, 1/8 W. , 1% 2.74 kft R55 Resistor

,

Metal Film, 1/8 W. , 1% 1.82 kft R56 Resistor

,

Metal Film, 1/8 W. , 1% 1.10 kft R57 Resistor

,

Metal Film, 1/8 W. , 1% 681 ft R58 Resistor

,

Metal Film, 1/8 W. , 1% 332 ft R59 Resistor

,

Metal Film, 1/8 W. , 1% 221 ft R60 Resistor

,

Metal Film, 1/8 W. , 1% 332 ft R61 Resistor

,

Metal Film, 1/8 W. , 1% 681 ft R62 Resistor

,

Metal Film, 1/8 W. , 1% 1.10 kft R63 Resistor, Metal Film, 1/8W. , 1% 1.82 kft R64 Resistor

,

Metal Film, 1/8 W. , 1% 2.74 kft R65 Resistor

,

Metal Film, 1/8 W. , 1% 909 ft R66 Resistor

,

Metal Film, 1/8 W. , 1% 3.57 ft R67 Resistor

,

Composition, 1/4 W. , 5% 100 ft R68 Resistor

,

Composition, 1/4 W. , 5% 100 ft R69 Resistor

,

Composition, 1/4 W. , 5% 470 ft R70 Resistor

,

Composition, 1/4 W. , 5% 470 ft R71 Resistor

,

Composition, 1/4 W. , 5% 15 kft R72 Resistor

,

Composition, 1/2 W., 5% 3.3 ft R7 3 Resistor

,

Composition, 1/4 W. , 5% 15 kft R74 Resistor

,

Composition, 1/2 W. , 5% 3.3 ft R75 Resistor, Composition, 1/4 W., 5% 10 kft R76 Resistor

,

Composition, 1/4 W. , 5% 10 ft R77 Resistor, Composition, 1/4 W., 5% 470 ft R78 Resistor

,

Composition, 1/4 W. , 5% 1 kft R79 Resistor

,

Composition, 1/4 W. , 5% 5.6 kft R80 Resistor, Composition, 1/8 W. , 5% 10 kft R81 Resistor , Composition, 1/4 W. , 5% 470 ft R82 Resistor

,

Composition, 1/4 W. , 5% 1 kft R83 Resistor, Composition, 1/4 W. , 5% 5.6 kft R84 Resistor , Composition, 1/4 W. , 5% 12 kft R85 Resistor, Composition, 1/8 W. , 5% 10 k ft R86 Resistor, Composition, 1/4 W. , 5% 5.6 k ft R87 Resistor, Composition, 1/4 W., 5% 5.6 k ft R88 Resistor, Composition, 1/2 W. , 5% 560 ft

12
Part Number Description Value

Card 2

R89 R90

R91

R92 R93

Resistor, Precision, 1/8 -W. , 0.1%

Resistor, Precision, 1/8 W. , 1% Resistor, Power, 3 Watt, 5%, Selected

Resistor, Power, 3 Watt, 5%, Selected

Selected

1100 kft ioo n ioo n

R4

R5

Resistor, Trimmer, 10 turn

Resistor, Trimmer, 10 turn

20 K Q

2 K n

R6 Selected

C19 Capacitor, Disc Ceramic 0.001 yF

C20 Capacitor, Disc Ceramic 0.001 P

F

C21 Capacitor, Plastic 0.1 yF, 100 V C22 Capacitor, Plastic 0.1 yF, 100 V C23 Capacitor, Disc Ceramic .01 yF, 50 V

C24 Capacitor, Tantalum 4.7 jjF, 25 V

C25 Capacitor, Disc Ceramic .01 yF, 50 V C26 Capacitor, Tantalum 4.7 pF, 25 V C27 Capacitor, Plastic 0.1 yF, 100 V C28 Capacitor, Tantalum 4.7 yF, 25 V

IC3 Operational Amplifier, Precision OP-05C

Q1 Transistor, Si, NPN 2N3904

Q2 Transistor, Si, NPN 2N3904

Q3 Transistor, Si, PNP 2N3906

Q4 Transistor, Si, PNP 2N3906

Q5 Transistor, Si, NPN 2N3904

Q6 Transistor, Si, NPN, Power 2N4922

Q7 Transistor, Si, PNP 2N3906

Q8 Transistor, Si, PNP, Power 2N4919

Q9 Transistor, Si, NPN 2N3904

Q10 Transistor, Si, PNP 2N3906

Qll Transistor, Si, NPN 2N3904

Q12 Transistor, Si, PNP 2N3906

Q13 Transistor, Si, PNP 2N3906

Q14 Transistor, Si, NPN 2N3904

Q15 Transistor, Si, Dual J-F.E.T. 2N5454

CR1 Diode, Signal, Ge 1N270

CR2 Diode, Signal, Ge 1N270

CR3 Diode, Signal, Ge 1N270

CR4 Diode, Signal, Si 1N4153

CR5 Diode, Signal, Ge 1N270

CR6 Diode, Signal, Si 1N4153

13
Part Number Description Value

Card 2

CR7 Diode, Signal, Ge IN270 CR8 Diode, Signal, Ge IN270

Card 1

R94 Resistor, Composition, 1/4 W, 5% 2.2 kn

R95 Resistor, Composition, 1/4 W, 5% 680 fi R96 Resistor, Composition, 1/4 W, 5% 2 Kfl R97 Resistor, Composition, 1/4 W, 5% 2.2 K « R98 Resistor, Composition, 1/4 W, 5% 680 n R99 Resistor, Composition, 1/4 W, 5% 2 Kfi

C29 Capacitor, Disc Ceramic 0.1 pF, 100 V

C30 Capacitor, Tantalum 4.7 PF, 25V

C31 Capacitor, Electrolytic 100 pF, 25V

C32 Capacitor, Disc Ceramic 0.01 PF, 50V

C33 Capacitor, Tantalum 10 PF, 25V

C34 Capacitor, Disc Ceramic 0.01 pF, 50V

C35 Capacitor, Disc Ceramic 0.1 PF, 100V

C36 Capacitor, Tantalum 4.7 PF, 25V

C37 Capacitor, Electrolytic 100 pF, 25V C38 Capacitor, Disc Ceramic 0.01 pF, 50V

C39 Capacitor, Tantalum 10 pF, 25V

C40 Capacitor, Disc Ceramic 0.01 pF, 50V

Q16 Transistor, Si, NPN 2N3904

Q17 Transistor, Si, NPN 2N697

Q18 Transistor, Si, PNP 2N3906

Q19 Transistor, Si, PNP 2N3638

1C11 Integrated Circuit, Regulator, +15V 7815

IC12 Integrated Circuit, Regulator, -15V 7915

CR9 Diode, Zener, 20V IN5250

CR10 Diode, Zener, 8.2V IN5237

CR11 Diode, Zener, 20V IN5250

CR12 Diode, Zener, 8.2V IN5237

Front Panel

gi Switch, Toggle, 2 pole, 2 position miniature

52 Switch, Rotary, 3 Section, 1 Pole, 9 Position,

Shorting. Centralab PSA208 or Equiv.

53 Switch, Rotary, 2 Section, 1 Pole, 11 Position,

Shorting, Centralab PSA204 or Equiv.

14
Part Number Description Value

Front Panel

L.E.D.

J-4

Diode, Light-emitting, Red

Connector, B.N.C., Female Panel Mount

S4 Switch, Rotary, Miniature, 2 Pole

,

2 Position

S8 Switch, Toggle, Miniature, 1 Pole, 2 Position

S9 Switch, Toggle, Miniature, 1 Pole, 2 Position

Front Panel - special built by NBS shops per attached drawing, figure 2-7.

Miscellaneous

Blank Plug--In Kit, double wide. Tektronix #040-0754-05 Connector , 20 Contact, .156" spacing TRW 251-10-30-160

or Equiv.

,

Keyed between 2-B and 3-C Connector

,

30 Contact, .156" Spacing TRW 251-15-30-160

or Equiv.

,

Keyed between 3-C and 4-D Connector

,

36 Contact, .156" Spacing TRW 251-18-30-160

or Equiv.

,

Keyed between 1-A and 2-B.

RFC1 R.F. Choke , Miniature 10 pH

RFC2 R.F. Choke , Miniature 10 pH

RFC3 R.F. Choke , Miniature 220 pH

RFC4 R.F. Choke , Miniature 220 pH

RFC5 R.F. Choke , Miniature 220 pH'

5 . Construction

This instrument is designed to be operated in and powered by a Tektronix TM-500 mainframe. It is built in a double-wide, blank, plug-in kit. There are three printed circuit boards. Figures 7-11 are photographs of the assembled instrument and the separate p.c. boards. Figures 12-14 are the art work for

the p.c. boards.

15
Figure 7 . Photo of assembled instrument (cover plates removed)

.

Figure 8. Rear view. (Partially disassembled)

16
Figure 9. P.C. Board ill.

Figure 11. P.C. Board #3.

17
-T

11.3 cm

4 7/16"

Parts Side 2:1

Figure 12. P.C. Board #1 art work.

18
L 20.6 cm ”

8 5 / 32 " Foil Side

Figure 13. P.C. Board #2 art work.

19
Parts Side

Figure 14. P.C. Board #3 art work.

20
6. Alignment Procedure

1. Using an extender cable, install the unit in a TM 500 mainframe (power off during insertion or removal). Turn on the power. Allow 30 minutes warm-up.

2. Power Supplies:

a. Check TP1 for + 15 V dc, + 5% (+0.75V).

b. Check TP 2 for -15 V dc, +5%.

c. Check TP 3 for +7.5 V dc, + 5%. (+0.4V)

d. Check TP4 for -7.5 V dc, + 5%.

3. Frequency Calibration:

a. Connect an accurate digital counter to TP5

.

b. Adjust Cl for a frequency of 1.000 MHz, +0.01%. (+100 Hz).

4. Voltage Reference:

a. Connect an accurate DVM (HP-3490 or equiv.) to TP6 (neg. lead to the ground TP).

b. Set S5 to normal.

c. Set the polarity switch, SI, to +

.

d. TP6 voltage should read 6.95 V +0.15 V.

5. +10 Volt Standard:

a. Connect the DVM to TP7.

b. Set mode switch, S9, to DC.

c. Set S5 to Null and S7 to Normal.

d. Adjust R2 for 0 volts, + 5 pV, at TP7.

e. Set S5 to Normal.

f. Adjust R1 for -10.000 volts, +2 mV, at TP7

.

g. Set the polarity switch, SI, to —

.

h. Check that TP7 voltage is + 10.000 volts, + 2 mV.

i. Set S7 to baseline check.

j. Check that TP7 voltage is 0 volts, + 20 pV.

k. Repeat steps c through j until specs are met.

£. Reset S5 and S7 to Normal.

6. AV Attenuator:

a. Connect the DVM to TP8.

b. Set S6 to Null.

c. Set the AV switch, S2, to 1 mV.

d. Set the Z Out switch, S4, to < 0.1 fi.

e. Adjust R3 for TP8 voltage of 0 pV + 0.5 pV.

f. Set S2 and S4 to all possible combinations and check that TP8 voltage remains at

0 pV ± 3-1/3 p V.

g. Reset S6 to Normal.

21
7.

Power Amplifier:

a. Set the multiplier switch, S3, to 0.

b. Set the sampler protection switch, S8, to Off.

c. Connect the DVM positive lead to TP11 and the negative lead to TP12.

d. Adjust the idle current pot, R5, for a DVM reading of +20 mV, + 20%.

e. Connect the DVM to TP10 (negative lead to the ground TP).

f. Adjust R4 for TP10 voltage of 0V, + 5 yV.

g. Repeat steps c through f until both specs, are met.

8.

Output Impedance:

a. Make up a nominal 50 ohm load using a wire wound, 50 £2 resistor of at least a 20 watt rating.

Solder a coaxial cable to the resistor. The other end of the coax should be terminated in a BNC plug which is connected to one arm of a BNC tee.

b. Using an accurately calibrated ohmmeter, measure the actual resistance of the 50 £2 load as seen

at the BNC tee. Record this value. R, , = ohms. load

c. Using the BNC tee connect both the 50 £2 load and the DVM to the BNC output connector.

d. Set the AV switch to 500 mV, the multiplier to 10, the Polarity to +, the mode to DC, the Sampler Protection to Off, and the Z Out to 50 £2.

e. Disconnect the 50 £2 load from the BNC tee.

f. Measure and record the output voltage. V , = mV. open ckt.

g. Compute the expected output voltage when the load is connected and the source resistance is precisely 50.00 £2.

V. , = V , R-. ,/ (R. , + 50.00 £2), load open ckt load load

Vload mV

.

h. Select an appropriate combination of R6 and R93 to be used and solder them to the circuit board.

i. Adjust R6 until the output voltage is precisely that calculated in step g.

j. The output resistance is now precisely 50.00 £2.

9.

The alignment is now complete.

22
7 . Performance Check and Calibration

1

.

Initial Set-Up

a. Check that all of the internal switches (S5, S6, and S7) are set to the Normal position.

b. Install the plug-in in the mainframe. (Power off during insertion or removal).

c. Turn on the power.

d. Set the polarity switch, SI, to +.

e. Set the mode switch, S9, to DC.

f. Set the sampler protection switch, S8, to Off.

g. Set the Z Out switch, S4, to < 0.1 £5.

h. Set the multiplier switch, S3, to 0.

i. Set the AV switch, 52, to 1 mV.

j. Connect a DVM (Fluke 8502A. or equiv.).

k. Allow 30 minutes warm-up.

2

.

DVM Zero Check

Check that the DVM reads 0 volts (+ 1 yV) on all of its ranges.

3.

Multiplier Attenuator Check

a. Set the DVM to the 10 V range.

b. Set the AV switch, S2, to 500 mV.

c. Set the multiplier switch, S3, to its various positions and record the DVM readings. Change

the DVM range as necessary. Compare the results to the specs, in the following table:

Multiplier Output Limits

Setting Voltage

1 0..500 V + 1.,3 mV

2 1.,000 V + 2.,5 mV

3 1.,500 V + 3. 8 mV

4 2..000 V + 5.,0 mV

5 2..500 V + 6. 3 mV

6 3.,000 V + 7.,5 mV

7 3.,500 V + 8.,8 mV

8 4.,000 V + 10..0 mV

9 4.,500 V + 11., 3 mV

10 5,.000 V + 12,.5 mV

Measured

Output Voltage

4

.

Polarity Check

a. Set the AV switch to 500 mV.

b. Set the multiplier switch to 10.

c. Switch the polarity switch, SI, between + and -. Record the DVM readings. They must read + 5.000V (±12.5 mV)

.

23
5 . AV Attenuator Check

a. Set the multiplier switch to 10.

b. Set the polarity switch to +. Set the AV switch to its various positions and record necessary. Compare the results to the specs, in the

AV Output Limits

Setting Voltage

500 5.000V +12.5 mV

200 2.000 V + 5.0 mV

100 1.000 V + 2.5 mV

50 500.0 mV + 1.25 mV

20 200.0 mV + 500 pV

10 100.0 mV + 250 pV

5 50.0 mV + 125 pV

2 20.00 mV + 50 pV

1 10.00 mV + 25 pV

Out Voltage Shift Check

. Set the Z Out switch. S4 , to 50 ft

. Set the AV switch to its various positions and record

necessary. Compare the results to the specs, in the :

AV Output Limits

Setting Voltage

500 10. 000 V + 25 mV

200 4. 000 V + 10 mV

100 2. 000 V + 5 mV

50 1. 000 V + 2.5 mV

20 400.0 mV + 1.0 mV

10 200.0 mV + 500 pV

5 100.0 mV + 250 pV

2 40 .00 mV + 100 pV

1 20 . 00 mV + 50 pV

Measured

Output Voltage

Change the DVM range as

Measured

Output Voltage

Z Out Impedance Check

a. Make up a nominal 50 ft load using a wire wound, 50 ft resistor of at least a 20 watt rating.

Solder a coaxial cable to the resistor. The other end of the coax should be terminated in a BNC plug which is connected to one arm of a BNC tee. Using an accurately calibrated ohmmeter, measure the actual resistance of the 50 ft load as seen

at the BNC tee. Record this value. R.load

ohms

.

Using the BNC tee connect both the 50 ft load and the DVM to the BNC output connector.

Set the AV, multiplier, and Z Out switches as shown in the table below. Record the DVM readings

with the load attached (V, ,) and also with the load disconnected (V ). Compute the out- load open ckt. put resistance, R , using the following equation:

24
R . = R, j (V , _ - V. ,)/Vn ,. out load open ckt . load load

In the < 0.1 £2 position the output resistance must be no larger than 0.15 £2. In the 50 £2 position the output resistance must be 50.00 £2, + 0.05 £2.

Z Out Switch

AV Switch

Multiplier

Switch ^load

Vopen ckt R

out

< 0.1 £2 500 mV 10 mV mV £2 50 £2 500 mV 10 mV mV £2

< 0.1 £2 20 mV 9 mV mV £2 50 £2 20 mV 9 mV mV £2

e. Disconnect the BNC tee and 50 £2 load from the output connector.

f. Set the multiplier switch to 0.

g. Set the Z Out switch to 1 M£2.

h. Using the DVM as an ohmmeter, connect it to the BNC output connector and measure the resistance.

Record this value. R (1M £2) = ohms. out

The output resistance must be 1.00 M£2, +1 k £2.

8

.

Overload Protection Check

a. Set the Z Out switch to < 0.1 £2.

b. Set the AV switch to 50 mV and the multiplier switch to 0.

c. Connect a milliampmeter (1A range) to the BNC output connector.

d. Increase the multiplier switch in steps and observe the Overload lamp. The output current threshold at which the lamp lights shall be at least 210 mA, but less than 240 mA. Overload Lamp Threshold = ma.

e. Set the AV switch to 500 mV and the multiplier switch to 10.

f. Measure and record the maximum output current. It shall be at least 250 mA but less than 300 mA.

I = mA. max.

g. Set the mode switch to 1 kHz and verify that the overload lamp is on. Return the switch to DC.

h. Set the Z Out switch to 50 £2 and verify that the overload lamp remains off.

i. Set the polarity switch to - and repeat steps b through h.

j. Remove the milliammeter from the output connector.

9 . Sampler Protection Check

a. Connect the DVM to the BNC output connector.

b. Set the polarity switch to +.

c. Set the AV switch to 200 mV, the multiplier to 0 and the Z Out to < 0.1 £2.

d. Increase the Multiplier setting one unit at a time. Note the output voltage. Then set the Sampler Protection switch to on and note the output voltage. The protection threshold is the first level at which a difference is noted in the two DVM readings. Record this level. This

threshold shall be at least 1.1 V but less than 1.5 V. The Overload lamp must also light when

the threshold is reached.

Protection Threshold = mV.

e. Set the AV switch to 500 mV, the Multiplier to 10, and the Z Out to 50 £2.

25
f. Measure and then record the output voltage. It must be less than 2.0 V. Protection Threshold = mV.

g. Set the polarity switch to - and repeat steps c through f.

0

.

Square Wave Operation Check

a. Set the AV switch to 500 mV, the Multiplier to 10, the Z Out to < O.lfi, and the polarity to +.

b. Connect an oscilloscope to the output.

c. A 5 volt square wave with a baseline of 0 volts should be observed.

d. Measure and record the rising and falling transition durations (10% - 90%). They must be less than 40 ps. The waveform must be clean with no perturbations such as overshoot or undershoot.

Transition Duration = ps.

e. Remove the oscilloscope.

f. Connect a frequency counter to the output.

g. Measure and record the square wave repetition rate. It must be 1.0 kHz + 0.01%. Frequency = kHz

.

1

.

Noise Output Check

a. Using a BNC cable connect the output to the input of an AC VTVM (HP-400 or equiv.) through a 50 Q BNC feed- thru termination.

b. Set the AV to 500 mV, Multiplier to 10, Z Out to 50 fi, mode to DC, and Sampler Protection to Off.

c. Measure and record the ac noise voltage. It must be less than 200 pV rms. Noise Voltage (high level) = pV rms.

d. Set the AV to 1 mV and the Multiplier to 1. e. Measure and record the ac noise voltage. It must be less than 25 pV rms. Noise Voltage (low level) = pV rms.

2.

The performance check and calibration is now complete.

26
NBS-114A (REV. 9-76)

' U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 81-1646

2. Gov't Accession No. 3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Amplitude Calibrator for Oscilloscopes

5. Publication Date April 1981

6. Performing Organization Code

7. AUTHOR(S)

James R. Andrews, Eugene E. Baldwin

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No.

.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, zip) 13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) The amplitude calibrator is designed to provide known dc voltage levels or 1 kHz square

waves from + 1 mV to + 5 V. It features selectable output impedances of < 0.1 ft, 50 , and 1 M ft. The instrument is designed with sufficient current capability to deliver

its indicated voltage into a 50 ft termination. To protect delicate sampling oscilloscopes, a limiter circuit can also be activated to limit the output voltage to + 1.8 V.

17. KEY WORDS (six to twelve entries ; alphabetical order; capi tali ze only the first letter of the first key word unless a proper name;

separated by semicolons)

Calibration; calibrators; instrumentation; oscilloscope calibrator; oscilloscopes

18. AVAILABILITY QQ Unlimited

I | For Official Distribution. Do Not Release to NTIS

I I Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

IX^Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

21. NO. OF

PRINTED PAGES

UNCLASSIFIED X 32

20. SECURITY CLASS

(THIS PAGE)

22. Price

X $6.00

UNCLASSIFIED

USCOMM-DC