Tektronix 103A Instruction Manual

INSTRUCTION MANUAL

MODEL 103A

NANOVOLT AMPLIFIER

0 COPYRIGHT 1974 0 COPYRIGHT 1974

KEITHLEY INSTRUMENTS. KEITHLEY INSTRUMENTS.

20775 AURORA ROAD CLEVELAND. OHIO R413Y ,216, 24~~0400 20775 AURORA ROAD CLEVELAND. OHIO R413Y ,216, 24~~0400

TELEX~ 98~5469 TELEX~ 98~5469

PRlNTED IN “.SA. PRlNTED IN “.SA.

CAOLE KEITHLEY CAOLE KEITHLEY

I NC. I NC.

CONTENTS

ILLUSTRATIONS

Fig. NO.

1
2
3

4
5
6

7a
7b
8

9
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12

13a
13b

14
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Ti,tle

Front Panel, wadcl, 103*.
Front Panel Controls and Terininal~s.
Rear Panel - Models 103A and 1031*.

overall Block ILt@-am.
Single-Ended Mode.
Uifferenrinl Mode.

Power Rcceptncle.
Power Ilqmfi connection.
Johnson Noise/ Hz Versus Source Resistance.
cain/Phnse vs. Frequency for R-C Type Filter.
Equivalent circuit Far Noise Analysis.
use Of Model 1037 Transformer.
Noise Bandwidth.
Noise CoDtoUr Single-Ended Mode.
Noise Contour Oiiferential Mode.
use as an cmill.oscope Preamplifier.
"se in System 84 Lockin Amplifier.
Model 2000 Rack Mounring.
Model 100, Dual Kack Mounting.
Overall Block r1i.ap,ram.
Non-inverting Stage "A".
Non-inverting stage '93".
Single-ended Mode.
"ifferenfisl Mode.
Nan-inverting stage "I?".

Nan-inverting Stage “F”.

High-Law cut Filter.
DC Offset Adjustment.

t18" Power supply.
camponent Layout, K-293.
component Layout, PC-294 (Mother Board).
Component Layout, PC-295 (Model 1031A Power Supply).
Component l.uyout, PC-261 (Model 1031A Regulator).
Tese Set-q For Frequency Response Check.
Chassis Assembly, Exploded View.
Bottom cover Assembly.

,‘URC

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SPECIFICATIONS

SPECIFICATIONS

0371

I<l3,‘?‘EIL.~-#

103A NANOVOLT AMPLIFIER

SECTION 1. GENERAL DESCRIPTION

l-l.

GENERAL. The Model 103A Nanovolt Amplifier is

an ac amplifier intended for use in high-gain low-

noise applications.

MODEL 103A AMPLIFIER

b. Adjustable frequency Sesponse. A combination of
high cut and low cut filter sections permit selection
of optimum irequency bandwidth.

C. Overload Indication.

An automaeic overload in­dication circuit detects overloads under various oper­ating conditions.

1-2. FEATURES.

d. High Output Level.

The full scale weput is ten

a. Selectable Input Mode. The input mode can be voles pk-to-pk (d-c coupled) to easily drive a recorder,

set far either single-ended or differential configura-

amplifier, or oscill~oscope without further amolification.

Front Panel Controls and Terminals

Control or Terminal

INPOT Switch (S201B)

A-B Input

-B Input

O"ERLO*o RESET Swiech (S201A)
3 dB FREO HZ Switch Sets overall amplifier frequency response.

HIGH Filter (S3"lA)

LOW Filter (S301B)

GAIN Switch CS302)

GAIN ADJUST Control (X306,

sets inpue “ode as follo”s:
“Ffferential Mode.
Single Ended Mode.

Activates overload reset circuitry.

Sets High Cue

sets LO" Cut
sets overall gain. in 20 dB steps.

Adjusts gain over 2” dS span.

Funceianal oescripekm

Paragraph

2-4, a
2-4, a

2-4, a
2-4, a

2-4, a
2-4, a

INPUT A cJ202~
INPUT B (5201~
HIGH "UT (53011
LOW "UT (53021

“vERL”A” Lamp toslol~

Control or Terminal

POWER INPUT (P301)

DC OUTPUT ADJ.

Control ii1 (R312)

Control 112 (R311)

2

Non-inverting

Inverting Input receptacle.

Input receptacle.

High output receptacle.

LOW output

receptacle.

Indicates overload condition.

Resr Panel Controla and Terminals

TABLE l-2.

Functional OescriptFon

Input receptacle for 518” power.

Adjusts dc oueput offsets.

2-2, a

2-2, a
2-2, b
2-2, b
2-5,

Paragraph

2-2, c

2-5, i

d

0371

INPUT MODE SELECTION

r

A-8 -J ""CRI."*D

INPIJC INPUT
5201

5201

%T

GENERAL DESCRIPTION

GAIN

ADJtJST SWiLCh

R306 s302

GAIN

INPUT

A

INPUT

""EilLOA"

B

FIGURE 2. Front Panel Controls and Terminals.

Lamp

LOW

FRCQ

HIGH
FREQ

5301 J-301
L."W
0 ,rr

IIICI,
"LT

"272

FIGURE 3. Rear Panel - Models 103A and 103ln

3

OPERATION

MODEL 103A AMPLIFIER

SECTION 2.

2-1. THEORY OF "PEKATION.

a. General. The Model 10311 Nanovolt hmplifier is

a high gain voltage amplifier designed for use with

single ended or differential inputs. 'The amplifier is

essentially composed of two high impedance inpue am-

plifiers, a summing amplifier, a combination high-l.ow

c,,t filter section, two stages of X10 gain, and an

output buffer amplifier as she"" in Figure 4.

b. Single-Ended Mode (-B INPUT). In this mode the

input amplifiers are connected together to form a
single-ended inverting amplifier as shown in Figure 5.
The signal at INPUT H will be amplified and inverted.
The signal at INPLTI A is not connected. Amplifiers

"A" and "s" are summed co provide very low noise char­acteristics.

Differential Mode (A-B INPUT). In this mode the

C.

input amplifiers are conneceed as separate amplifiers
which are summed differentially as shown in Figure 6.
The oueput is a funceion of A-B times the gain of the

amplifier.

OPERATION

2-2. C”NNIICTI”NS.

Input. 'I‘he

a.
designated "INPUT A" and "INPUT il". 'These receptacles
(5201 and 5202) at-2 BNC types which mate with coaxial
cables such as Keithlcy Models 8201 and 8202 coaxial
cables. 'he inner coneact of each receptacle is the
circuit high. The outer shell ia the circuit low

which is floati,"g wit,, respect co the Model l"3h chas-

sis. Only INPUT B should be used for single-ended
input operation. For differential operation both in­puts should be used.

modes is given in Section 2-5.

b. output.

cles designated "LOW "UT" and "HIGH "UT". These re-

ceptacles (5301 and 5302) are BNC types which mate

with coaxial cables such as Keithley Models 8201 and

8202

coaxial cables. The inner ConfaCt of "LOW am@'"
receptacle is at ci.rcuit low (the same as the outer
shell of INPUT A and INPUT B). The inner contact of
"HIGIl OUT" is the amplified output. me outer shell
of each ""UT" connectc,r is at chassis ground. There

Model 103A has two input receptacles

A complete discussion of input

the b,odel 103A has two oueput recepce-

INPUT6

INPUTA

“A”

FIGURE 4.

Overall Block Diagram.

FIGURE 6. Diffcrcntial Mode

4

“371

CHASSIS

INPUT E

+1t3v 8 D -18V

@

c

P301

LOW

INPUT A

,,.

,,,~;

;..,,

OPERATION

2.

Flicker noise (l/f). 'this noise has a char­acteristic of constant energy per percent bandwidth.
Random noise such as generated by tubes and trans-

istors shows a low frequency characteristic or l/f

relafionship.

3. oiscrete Frequency Noise. This is noise gen-

erated by various discrete frequency sources such
as power lines, radio frequency generators, etc.

b. Shielding.

1. Electric Fields.

Shielding is usually neces­sary when the instrument is in the presence of very
large ac fields or when very sensitive measurements

are being made. The shields of the measurement cir­cuit and leads should be connected together to ground

at only one point.

This provides a "tree" configura-

tion, which minimizes ground loops.

2. Magnetic Fields. Magnetic shielding is useful

where very large magnetic fields are present. Shield-

ing, which is available in the form of plates, foil
or cables, can be used to shield the measuring cir-

cuit, the lead wires, or the instrument itself.

c. Grounding. The Model 103A has been designed to
operate with either the Model 1031A Power Supply or

the Model 840 Amplifier. The circuit low is isolated
from chassis ground by a 10 ohm resisror in the power
supply. For best results, no other connection should

be made between circuit low and chassis ground. Since

the yodel 103.4

chassis is connected to earth ground
through the accessory power cable, it is not necessary
to connect the Model 10% chassis to ground.

when the

yodel 103~ is connected to the yodel 840 differential

inouc (as shown in FFrwre 15). the m!xR of the Model
840 minimizes the effects of ground loops.

a. Front Panel.

1. INPUT Switches (52018). These switches are
pushbutton types wit,, two "orma configurations. The
switch posi~i.ons are designated as "A-B" and "-U".
'These two pushbuttons are interlocked so that depress­ing one will release the Other automatically. H0C.T"~~

it is

possible

to depress both or have

both buttons
released but these conditions are not useable modes
Of operation.

2. O"EKLOA,l RESET Switch (S2Olh). This switch is
a momentary contact pushbutton type. The overload
reset circuit is activared only when the pushbutton
is depressed. When the OVERLOA" lndicaeor light goes
off the reset has been accomplished.

3dn FKEQ Hz (5301).

3.

concenrric type.

filter in ten positions from 10 11% co 300 k"Z.

'l'he inner dial sets the "IlIGil Cut"

This switch is a dual-

me

outer dial sets the "LOW Cut" filter in nine posi-

tions from 0.1 to 10 kllz.

4. GAIN.

Gain is set by use of a dual-concentric
GAIN switch 5302 and GAIN ADJUST control R306. The
GAIN hD.JUST control has a "CAL" position when set

to fully clockwise.

b. Rear Panel.

1. DC OUTPUT AOJ "1" (R312).

These controls adjust
the dc output offset.

6

FIGURE 9. Gain/Phase Vs. Frequency For R-C Type Filter.

0371

0371

7

MODEL 103A AMPLIFIER

Gain settings of Model l”3A

TABLE 2-3.

CAIN switch GAIN AD.J”ST

Overall Gain

setting setting (C) Possible

Of the IIICII-LOW cut filter which may not cause an
overload at the ourpuc. since a &refilter oVerload
may occur due t" large amplirude noise signals, the
overload is sensed and the OVERLOAD indicator is
lighted whenever an overload condition is present.

However, prefilter overloads above 100 km may not
be detected.

the output stages due tc’ saturation.

put will saturate when drive" beyond 10 volts &peak-

d. Overloads. Although clle Model 103A aaplifier is
ac coupled to the input, rtle amplifier has been designed
to have a very low frequency response. Therefore the

internal circuits have very long time constants. me
long time COnSrantS affect the operation of the Model

103A under input overloads and power turn-on

Three types of overloads must be considered in this

discussion.

conditions.

ra-peak, the OVERLOAD indicaror will be lighted as
long as t,,i.s canditian cxiscs.

lOad condition, the GAIN setting can be reduced, the
input signal can be attenuated, or fil~Lered through
the use of the HIGH-LOW cut filters. The O"CRI.oAD

K1:SF.T button can be used t0 restablish normal bias

conditions in the amplifier.

Calibrated

(Yes or NO)

wefilter ""erloads. Overloads can occur ahead

2.

3. Steady-state Overloads.

Overloads can occur in

Since the WC-

TO remove ibe "Ye=-

0371

“opt =

Eq. 6a

MODEL1037

Thus the equivalent noise bandwidth is given in equa­tion 10.

10

OPERATION

0371

APPLICATIONS

MODEL 1038 AMPLIFIER

SECTION 3.

3-1.

GENERAL. AlthouSh the Model 103A can be used as

El general purpose insfrument, a few specific applica-

tions Can more fully illustrate the important features.

3-2.

TYPICAL APPLICATIONS.

a. Oscilloscope Preamplifier. men used as a pre­amplifier for a dull input oscilloscope the Model 103A
CB” be connected as shown in Figure 14.
scope chassis should be conneceed to earth ground di­rectly. The Model 10%. out,,uts can be connect differ-

entially or single-ended if necessary.

ing the Model 103A output to a single input oscillo­scope, the NIGH OUT receptacle should be used.
the Model 103A low is isolated by 10 ohms above chassis

ground when powered by the Model 1031A, no other con­nection is required. If another power supply is used
such as batteries, it is necessary to connect a 10 ohm
resistor between low and chassis.

b. Lock-in.System Preamplifier. When used with a
phase-sensitive detector such as the Keithley Model
840 the Model 103A can be connected as shown in Figure

15. In this application the Model 103A outputs mate
with the differential input of the Model 840 thereby

minimizing ehc effects of ground loop connections.

this application

input “ode.

pr.ovides law and ground as well as +I8 volts, it is
not necessary to connect the Model 103A chassis to
earth Sround.

the Model 840 should be set for “01~~”

Since the Model 840 accessory power outpx,t

me oscillo-

men c”nnect-

Si”CC

For

APPLICATIONS

F10Lnuz 14.

FIGURE 15. “se in System 84 Lockin Amplifier.

Use as an Oscilloscope Preamplifier.

OSCILLOSCOPE

POWER GND