Ortec 408 User manual

PRECISION

INSTRUMENTATION

FOR

RESEARCH

Oak

Ridge

Technical

Enterprises

Corporation

OAK

RIDGE,

TENNESSEE

INSTRUCTION

MANUAL

MODEL

408

BIASED

AMPLIFIER

INSTRUCTION

MANUAL

MODEL

408

BIASED

AMPLIFIER

Serial

No.

Purchaser

Date

issued

OAK

RIDGE

TECHNICAL

ENTERPRISES

CORPORATION

p.

O.

BOX

C

OAK

RIDGE,

TENNESSEE

Telephone

(615)

483-8451

TWX

810-572-1078

I

Oak

Ridge

Technical

Enterprises

Corporation

1966

Printed

in

U.S.A.

CONTENTS

1.

DESCRIPTION

1.1

General

Description

1.2

Description

of

Basic

Function

2.

SPECIFICATIONS

2.1

General

Specifications

2.2

Biased

Amplifier

Specifications

3.

INSTALLATION

3.1

General

Installation

Considerations

3.2

Connection

to

Power—Nuclear

Standard

Bin,

ORTEC

Model

401/402

3.3

Connection

to

Linear

Amplifier

4.

OPERATING

INSTRUCTIONS

4.1

Front

Panel

Controls

4.2

Initial

Testing

and

Observation

of

Pulse

Waveforms

4.3

Connector

Data

4.4

Typical

Operating

Considerations

5.

CIRCUIT

DESCRIPTION,

Biased

Amplifier

(Etched

Board

408-0148)

6.

MAINTENANCE

6.1

Testing

Performance

of

Biased

Amplifier

6.2

Biased

Amplifier

Threshold

and

Pedestal

Adjustment

6.3

Suggestions

for

Troubleshooting

6.4

Tabulated

Test

Point

Voltages

on

Etched

Board

7.

PARTS

LIST

8.

BLOCK

DIAGRAMS

AND

SCHEMATICS

408-0148-Bl

Model

408

Block

Diagram

408-0148-Sl

Model

408

Biased

Amplifier

Schematic

408-0201-S

Model

408

Chassis

Wiring

Schematic

STANDARD

WARRANTY

FOR

ORTEC

ELECTRONIC

INSTRUMENTS

DAMAGE

IN

TRANSIT

Shipments

should

be

examined

immediately

upon

receipt

for

evidence

of

external

or

con

cealed

damage.

The

carrier

making-delivery

should

be

notified

immediately

of

any

such

damage,

since

the

carrier

is

normally

liable

for

damage

in

shipment.

Packing

materials,

waybills,

and

other

such

documentation

should

be

preserved

in

order

to

establish

claims.

After

such

notification

to

the

carrier,

notify

ORTEC

of

the

circumstances

so

that

we

may

assist

in

damage

claims

and

in

providing

replacement

equipment

when

necessary.

WARRANTY

ORTEC

warrants

its

electronic

products

to

be

free

from

defects

in

workmanship

and

materials,

other

than

vacuum

tubes

and

semiconductors,

for

a

period

of

twelve

months

from

date

of

ship

ment,

provided

that

the

equipment

has

been

used

in

a

proper

manner

and

not

subjected

to

abuse.

Repairs

or

replacement,

at

ORTEC

option,

will

be

made

without

charge

at

the

ORTEC

factory.

Shipping

expense

will

be

to

the

account

of

the

customer

except

in

cases

of

defects

discovered

upon

initial

operation.

Warranties

of

vacuum

tubes

and

semiconductors,

as

made

by

their

manufacturers,

will

be

extended

to

our

customers

only

to

the

extent

of

the

manufacturers'

liability

to

ORTEC.

Specially

selected

vacuum

tubes

or

semiconductors

cannot

be

warranted.

ORTEC

reserves

the

right

to

modify

the

design

of

its

products

without

incurring

responsibility

for

modification

of

previously

manufactured

units.

Since

installation

conditions

are

beyond

our

control,

ORTEC

does

not

assume

any

risks

or

liabilities

associated

with

the

methods

of

instal

lation,

or

installation

results.

QUALITY

CONTROL

Before

being

approved

for

shipment,

each

ORTEC

instrument

must

pass

a

stringent

set

of

quality

control

tests

designed

to

expose

any

flaws

in

materials

or

workmanship.

Permanent

records

of

these

tests

are

maintained

for

use

in

warranty

repair

and

as

a

source

of

statistical

information

for

design

improvements.

REPAIR

SERVICE

ORTEC

instruments

not

in

warranty

may

be

returned

to

the

factory

for

repairs

or

checkout

at

modest

expense

to

the

customer.

Standard

procedure

requires

that

returned

instruments

pass

the

same

quality

control

tests

as

those

used

for

new

production

instruments.

Please

contact

the

factory

for

instructions

before

shipping

equipment.

ORTEC

ij

MODEL

408

i/

BIASED

AMPLIFIER

i

BIAS

LEVEL

20

GAIN

INPUT

OUTPUT

^

■P

MODEL

408

BIASED

AMPLIFIER

1-1

MODEL

408

BIASED

AMPLIFIER

1.

DESCRIPTION

1.1

General

Description

The

Model

408

is

a

modular

Biased

Amplifier

designed

to

be

used

with

pulse

amplifiers,

such

as

the

ORTEC

Model

410,

that

provide

a

unipolar

or

bipolar

output

pulse,

with

either

RC

or

delay

line

shaping.

When

used

with

the

Model

410

Multimode

Amplifier,

the

combination

offers

high

counting

rate

capability,

good

overload

recovery,

and

the

ultimate

in

resolution

performance

necessary

for

use

with

semiconductor,

gaseous,

or

scintillation

detectors.

All

input

and

output

signal

levels

and

impedances

are

compatible

with

other

modules

in

the

ORTEC

400

Series.

1.2

Description

of

Basic

Function

The

Model

408

Biased

Amplifier

provides

a

variable

step

gain

of

1

to

20

in

a

1-2-5

sequence

to

expand

a

region

of

interest

in

a

spectrum

and

thereby

more

fully

utilize

the

capabilities

of

multichannel

analyzers

in

high

resolution

spectroscopy.

The

bias

level,

above

which

amplification

occurs,

is

controllable

by

a

10-turn

control

which

spans

the

linear

input

signal

range.

The

input

may

be

from

any

source

of

linear

signals

having

no

more

than

a

10-volt

span,

e.g.,

the

Model

410

Multimode

Amplifier,

the

Model

415

Sum-Delay

Amplifier,

or

the

linear

output

of

the

Model

409

Linear

Gate

and

Slow

Coincidence.

Circuit

features

of

the

Model

408

Biased

Amplifier

include

a

baseline

restoration

network

that

sets

the

input

back

to

zero

with

a

minimum

of

dead

time

and

offset,

and

an

amplitude

limiter

for

prompt

recovery

from

overload

pulses.

The

input

will

accept

either

unipolar

or

bipolar

signals,

but

the

output

is

only

positive

unipolar,

the

negative

portion

being

clipped

in

passing

through

the

biased

section

of

the

amplifier.

2-1

2.

SPECIFICATIONS

2.1

General

Specifications

The

Model

408

is

housed

in

a

Nuclear

Standard

Module;

it

is

one

standard

module

wide

and

weighs

2.4

pounds.

The

module

contains

no

internal

power

supply

and

therefore

must

obtain

the

necessary

operating

power

from

a

Nu

clear

Standard

Bin

and

Power

Supply

such

as

the

ORTEC

Model

401/402.

All

signals

in

and

out

of

the

module

ore

on

front

panel

BNC

connectors,

and

the

input

power

is

via

the

standard

connector

on

the

rear

panel.

2.2

Biased

Amplifier

Specifications

Input

Unipolar

or

bipolar

(with

the

positive

portion

leading);

0.2V

to

lOV

rated

range,

12

volts

maximum

Input

Impedance

125

ohms

Gain

1

to

20

in

steps

of

1-2-5-10-20

Bias

Range

,

0

to

90%

of

rated

span

Output

0

to

lOV

rated

span,

12V

maximum;

posi

tive

pulse

only

Output

Impedance

Approximately

1

ohm,

short-circuit

pro

tected

Linearity.

Integral

nonlinearity

less

than

0.2%

from

0.2V

to

8V,

0.3%

to

lOV,

taken

with

1-

fxsec

RC

shaped

pulse

and

minimum

bias

level

Temperature

Stability

Gain

shift

less

than

0.01%

per

°C

per

gain

factor

Operating

Temperature

Range

0

to

50°C

Power

Required

+24V,

59

mA

+

12V,

3

mA

-12V,

13

mA

-24V,

53

mA

Mechanical

One

module

wide

and

designed

to

meet

the

recommended

interchangeability

standards

set

out

in

AEG

Report

TID-

20893;

1.35

inches

wide,

8.75

inches

high,

and

9.75

inches

long.

3-1

INSTALLATION

3.1

General

Installation

Considerations

The

Model

408

Biased

Amplifier,

used

in

conjunction

with

o

Model

401/402

Bin

and

Power

Supply,

is

intended

for

rack

mounting

and

therefore

it

is

nec

essary

to

ensure

that

vacuum

tube

equipment

operating

in

the

same

rack

with

the

Model

408

have

sufficient

cooling

air

circulating

to

prevent

any

lo

calized

heating

of

the

all-transistor

circuitry

used

throughout

the

Model

408.

The

temperature

of

equipment

mounted

in

racks

can

easily

exceed

the

recom

mended

maximum

unless

precautions

are

taken;

the

Model

408

should

not

be

subjected

to

temperatures

in

excess

of

120°F

(50°C).

3.2

Connection

to

Power—Nuclear

Standard

Bin,

ORTEC

Model

402/402

The

Model

408

contains

no

internal

power

supply

and

therefore

must

obtain

power

from

a

Nuclear

Standard

Bin

and

Power

Supply

such

as

the

ORTEC

Model

401/402.

It

is

recommended

that

the

bin

power

supply

be

turned

off

when

inserting

or

removing

modules.

The

ORTEC

400

Series

is

designed

so

that

it

is

not

possible

to

overload

the

bin

power

supply

with

a

full

complement

of

modules

in

the

Bin;

however,

this

may

not

be

true

when

the

Bin

contains

mod

ules

other

than

those

of

ORTEC

design.

In

such

instances,

the

power

supply

voltages

should

be

checked

after

the

insertion

of

modules.

The

ORTEC

Model

401/402

has

test

points

on

the

power

supply

control

panel

to

monitor

the

dc

voltages.

When

using

the

Model

408

outside

the

Model

401/402

Bin

and

Power

Supply,

be

sure

that

the

jumper

cable

used

properly

accounts

for

the

power

supply

grounding

circuits

provided

in

the

recommended

AEC

standards

of

TID-

20893.

Both

clean

and

dirty

ground

connections

ore

provided

to

ensure

proper

reference

voltage

feedback

into

the

power

supply,

and

these

must

be

pre

served

in

remote

cable

installations.

Care

must

also

be

exercised

to

avoid

ground

loops

when

the

module

is

not

physically

in

the

bin.

3.3

Connection

to

Linear

Amplifier

The

input

to

the

Model

408

is

on

the

front

panel

INPUT

BNC

connector,

and

is

compatible

with

all

linear

unipolar

or

bipolar

signals

from

the

outputs

of

linear

amplifiers,

linear

gates,

delay

amplifiers,

etc.

The

input

impedance

is

125

ohms,

ac

coupled,

and

the

input

operating

range

is

from

threshold,

typ

ically

100

millivolts,

to

10

volts.

It

is

important

that

no

external

terminators

be

added

to

the

INPUT

BNC

on

the

Biased

Amplifier

unless

it

is

determined

before

hand

that

the

driving

source

can

drive

the

combination

load

of

the

Model

408

125-ohm

input

impedance

and

the

external

terminator

in

parallel.

3-2

3.4

Linear

Output

Signal

Connections

and

Terminating

Impedance

Considerations

The

source

impedance

of

the

0-10

volt

standard

linear

outputs

of

most

400

Series

modules

is

approximately

1

ohm.

Interconnection

of

linear

signals

is,

thus,

non-critical

since

the

input

impedance

of

circuits

to

be

driven

is

not

important

in

determining

the

actual

signal

span,

e.g.,

0-10

volts,

de

livered

to

the

following

circuit.

Paralleling

several

loads

on

a

single

out

put

is

therefore

permissible

while

preserving

the

0-10

volt

signal

span.

Short

lengths

of

interconnecting

coaxial

cable

(up

to

approximately

4

feet)

need

not

be

terminated.

However,

if

a

cable

longer

than

approximately

4

feet

is

necessary

on

a

linear

output,

it

should

be

terminated

in

a

resistive

load

equal

to

the

cable

impedance.

Since

the

output

impedance

is

not

purely

resistive,

and

is

slightlydifferent

for

each

individual

module,

when

a

certain

given

length

of

coaxial

cable

is

connected

and

is

not

terminated

in

the

characteristic

impedance

of

the

cable,

oscillations

will

generally

be

observed.

These

oscillations

can

be

suppressed

for

any

length

of

cable

by

properly

terminating

the

cable

either

in

series

at

the

sending

end

or

in

shunt

at

the

receiving

end

of

the

line.

To

properly

terminate

the

cable

at

the

receiving

end,

it

maybe

necessary

to

consider

the

input

impedance

of

the

driven

circuit,

choosing

an

additional

parallel

resistor

to

make

the

combination

produce

the

desired

termination

resistance.

Series

terminating

the

cable

at

the

sending

end

may

be

preferable

in

some

cases

where

re

ceiving

and

terminating

is

notdesirable

or

possible.

When

series

terminat

ing

at

the

sending

end,

full

signal

span,

i.e.,

amplitude,

isobtainedat

the

receiving

end

only

when

it

is

essentially

unloaded

or

loaded

with

an

impedance

many

times

that

of

the

cable.

This

may

be

accomplished

by

inserting

a

series

resistor

equal

to

the

characteristic

impedance

of

the

ca

ble

internally

in

the

module

between

the

actual

amplifier

output

on

the

etched

board

and

the

output

connector.

It

must

be

remembered

that

this

impedance

is

in

series

with

the

input

impedance

of

the

load

being

driven,

and

in

the

case

where

the

driven

load

is

900

ohms,

a

decrease

in

the

signal

span

of

approximately

10%

will

occur

for

a

93-ohm

transmission

line.

A

more

serious

loss

occurs

when

the

driven

load

is

93

ohms

and

the

transmis

sion

system

is

93

ohms.

In

this

case,

a50%

loss

will

occur.

BNC

connec

tors

with

internal

terminators

are

available

from

a

number

of

connector

manufacturers

in

nominal

values

of

50,

100,

and

lOOOohms.

ORTEC

stocks

in

limited

quantity

both

the

50

and

100

ohm

BNC

terminators.

The

BNC

terminators

are

quite

convenient

to

use

in

conjunction

with

a

BNC

tee.

4-1

4.

OPERATING

INSTRUCTIONS

4.1

Front

Panel

Controls

GAIN

The

voltage

gain

of

the

Model

408

Biased

Amplifier

is

controlled

by

the

GAIN

s\A/itch.

The

gain

is

applied

to

the

input

signal

that

exceeds

the

dc

BIAS

LEVEL.

The

gain

covers

the

range

of

1

to

20

in

a

1-2-5-10-20

sequence.

BIAS

LEVEL

A

continuously

adjustable

dc

bias

voltage

ranging

from

0

to

9V

is

provided

to

bias

out

a

fixed

level

of

all

input

pulses

to

the

Biased

Amplifier.

The

resultant

signal,

i.e.,

the

portion

of

the

input

signal

above

the

bias

level,

is

then

ampli

fied

by

an

amount

determined

by

the

setting

of

the

Biased

Amplifier

GAIN

switch.

4.2

Initial

Testing

and

Observation

of

Pulse

Waveforms

Refer

to

Section

6.1

of

this

Manual

for

information

concerning

data

obtained

during

initial

testing.

4.3

Connector

Data

PGl

-

INPUT

BNC

Connector

Input

impedance

is

125

ohms,

ac

coupled.

The

input

voltage

rated

range

is

0

to

lOV,

with

a

maximum

of

12V.

The

input

may

be

shunted

from

its

125-ohm

input

impedance

if

necessary

to

terminate

transmission

lines

that

have

im

pedances

other

than

1

25

ohms.

In

shunting

the

input

impedance,

care

must

be

taken

to

ensure

that

the

driving

source

can

drive

the

resultant

low

input

im

pedance.

PG2-OUTPUT

BNC

Connector

Output

driving

impedance

is

approximately

1

ohm

and

is

short-circuit

pro

tected.

OUTPUT

Test

Point

An

oscilloscope

test

point

is

available

for

monitoring

the

signal

on

the

OUTPUT

BNC

connector.

This

test

point

has

a

470-ohm

series

resistor

connecting

it

to

the

OUTPUT

BNC

connector.

Power

Connector

The

Nuclear

Standard

Module

power

connector

is

an

AMP

202515-5*

4.4

Typical

Operating

Considerations

The

output

signal

of

the

Model

408

must

be

closely

monitored

when

using

RC

shaped

input

pulses.

This

is

also

true

if

a

large

amount

of

integration

is

used

with

delay

line

shaped

pulses.

The

reasoning

behind

this

can

be

pointed

out

by

examining

the

resultant

pulse

shape

illustrated

in

Figure

4-1.

With

the

BIAS

LEVEL

set

at

level

A,

it

can

be

noted

that

the

output

pulse

width

of

the

Model

408

at

the

baseline

will

be

from

A

to

A';

i.e.,

the

baseline

width

is

equal

to

the

time

the

input

signal

E|,,

is

above

the

BIAS

LEVEL.

For

the

BIAS

LEVEL

A

in

Figure

4-1,

the

output

pulse

of

the

Model

408

will

be

satisfactorily

shaped

to

be

used

as

an

input

to

most

multichannel

analyzers.

However,

the

res.ultant

4-2

Model

408

output

pulse

for

BIAS

LEVEL

B

will

hove

a

pulse

width

at

the

base

line

equal

to

the

time

from

B

to

B'

in

Figure

4-1.

With

the

Biased

Amplifier

gain

applied

to

the

portion

of

the

input

signal

Ein

that

is

above

the

BIAS

LEVEL

B,

it

is

seen

that

the

resultant

Model

408

output

pulse

is

much

too

narrow

to

be

satisfactorily

used

as

an

input

signal

to

the

majority

of

available

multichannel

analyzers.

For

double

RC

shaped

signals

with

0.5-microsecond

integration

and

differentiation

time

constants,

the

time

between

B

and

B'

can

easily

be

as

short

as

0.5

microsecond.

For

the

above

reasons,

an

ORTEC

Model

41

1

Pulse

Stretcher

is

recommended

for

applications

involving

the

Model

408

Biased

Amplifier.

The

Pulse

Stretcher

will

stretch

the

peak

amplitude

of

the

output

signal

from'the

Model

408

for

a

minimum

of

1.5

microseconds,

thereby

im

proving

the

system

linearity

by

reducing

the

bandwidth

requirements

of

the

multichannel

analyzer

analog-to-digital

converter

(ADC).

!•

BIAS

LEVEL

B

r

BIAS

LEVEL

A

1

iJSEC

Figure

4-1.

Bipolar

RC

Shaped

Input

Pulse

5-1

CIRCUIT

DESCRIPTION,

BIASED

AMPLIFIER

(Etched

Board

408-0148)

5.1

From

Drawings

408-0148-Bl

and

408-0148-51,

the

following

functions

con

be

recognized

in

the

Biased

Amplifier:

a

baseline

recovery

network

consisting

of

Ql,

D2,

03,04,

and

Q3

(also

called

the

dc

restoration

network).

Q2

constitutes

a

dc

emitter

follower

that

establishes

the

bias

level

at

the

input

to

the

Biased

Amplifier.

Q4

is

an

emitter

follower

that

drives

the

linear

gate

section

of

the

Biased

Amplifier

(Q5

and

Q7),

and

also

drives

the

Schmitt

trigger

circuit

(Ql

1

and

012)

via

the

0.70

limiter

(012,

013,

and

014).

The

linear

gate

is

opened

by

the

application

of

a

positive

signal

through

C4

to

the

base

of

08,

which

causes

the

current

switch

to

transfer

its

emitter

current

flowing

through

R8

from

06

to

08.

When

08

conducts

the

emitter

current

of

the

current

switch,

the

base

drive

current

to

05

is

available

via

R6,

and

concurrently,

base

cur

rent

for

07

becomes

negligible,

since

the

collector

of

08

requires

approxi

mately

4

milliamperes.

With

the

current

switch

conducting

current

in

08,

it

can

be

seen

that

05,

the

series

element,

is

in

heavy

saturation,

with

the

base

drive

current

supplied

from

R6

flowing

into

the

base

through

the

emitter

and

back

to

the

emitter

of

04,

a

low

impedance

voltage

source.

Also,

07,

the

shunt

ele

ment

in

the

linear

gate,

is

now

back

biased

and

presents

a

high

shunt

impe

dance

to

signals

flowing

through

the

saturated

series

element,

05.

The

output

of

the

linear

gate

is

taken

from

the

collectors

of

05

and

07.

The

output

of

the

linear

gate

is

followed

by

a

cascode

emitter

follower,

09

and

010.

The

output

of

emitter-follower

09

and

010

is

fed

through

a

gain

control

switch

and

then

through

two

amplifying

loops

similar

to

the

loops

shown

in

Figure

5-1.

-24

V

R

in

-y\AA-

in

-»■

e

i

in

_rx.

\

Qa

+

24

V

If^

■vW^

6ND

Figure

5-1.

Basic

Feedback

Amplifier

Loop

!•

5-2

The

bias

level

is

set

by

the

1

K

helipot;

then,

the

dc

bios

level

is

fed

through

the

baseline

recovery

network

in

such

a

way

that

the

bias

level

is

approximately

equal

to

the

dc

potential

on

the

base

of

Q4.

Diode

D6

prevents

the

emitter

potential

of

emitter-follower

Q4

from

going

more

negative

than

approxi

mately

0.6

volts

due

to

the

BIAS

LEVEL

control.

With

the

application

of

a

positive

input

signal,

on

2

of

the

Biased

Amplifier

board,

that

is

equal

to

or

exceeds

the

bias

level

dc

potential,

emitter-follower

Q4

will

be

forward

biased

and

its

emitter

potential

will

be

equal

to

the

po

tential

of

the

input

pulse

minus

the

dc

bias

level

voltage.

The

positive

pulse

generated

at

the

emitter

of

Q4

is

fed

in

parallel

to

two

circuits

—to

the

emitter

of

Q5

and

to

the

cathode

of

D12.

The

combination

of

series

transistor

Q5

and

shunt

transistor

Q7

forms

a

linear

gate.

The

switching

of

the

linear

gate

from

its

normally

closed

position,

i.e.,

Q5

back-biased

and

Q7

saturated,

to

the

open

position

is

controlled

by

the

current

switch,

Q6

and

Q8.

The

current

switch

is

activated

by

the

application

of

a

positive

pulse

at

the

base

of

Q8.

The

positive

pulse

necessary

to

trigger

the

current

switch

is

generated

at

the

collector

of

Q1

2.

Transistors

Q1

1

and

Q1

2

constitute

a

Schmitt

trigger

discrim

inator

circuit

that

is

triggered

when

the

pulse

amplitude

of

the

input

signal

on

2

exceeds

the

bios

level

by

100

millivolts.

The

appearance

of

a

100-milli-

volt

positive

pulse

at

the

emitter

of

Q4

is

coupled

to

the

trigger

circuit,

Q11

and

Q12,

through

the

diode

network,

D12

and

D13.

The

positive

pulse

applied

to

the

cathode

of

D12

back-biases

D12,

thereby

shunting

the

V2-mil

liampere

current

normally

flowing

through

D12,

through

diode

D13,

and

then

through

the

parallel

combination

of

D14

and

R45.

Since

R46

constitutes

a

constant

current

generator

of

approximately

1

milliampere,

and

R45

constitutes

a

con

stant

current

sink

of

approximately

0.5

milliampere,

turning

off

diode

D12

will

force

the

additional

V2

milliampere

to

flow

in

the

combination

D13, D14,

and

R45.

When

the

additional

V2

milliampere

is

transferred

from

012,

transistor

Q1

1

will

be

forward

biased,

causing

the

Schmitt

trigger

circuit,

Q1

1

and

Q12,

to

trigger

and

remain

triggered

for

the

duration

of

the

input

pulse

that

exceeds

the

bias

level

by

ICQ

millivolts.

Since

Q12

is

normally

conducting,

the

trigger

action

will

transfer

the

current

from

Q1

2

to

Q1

1,

thereby

generating

a

positive

pulse

at

the

collector

of

Q12;

this

pulse

is

then

coupled

to

the

base

of

Q8

and

activates

the

current

switch,

Q6

and

Q8.

Transistor

Q6

in

the

current

switch

is

normally

conducting,

but

the

application

of

a

positive

signal

to

the

base

of

Q8

causes

Q6

to

cease

conduction

and

Q8

to

conduct

heavily.

When

Q6

ceases

conduction,

the

current

flow

flowing

through

R6

is

switched

from

the

collector

of

Q6

into

the

base

of

Q5,

thereby

causing

Q5

to

go

into

heavy

saturation.

In

a

similar

manner,

the

heavy

conduction

of

transistor

Q8

removes

the

available

base

current

for

Q7,

causing

Q7

to

be

turned

off.

With

Q5

in

heavy

saturation

and

Q7

turned

off,

the

action

of

the

linear

gate

is

evident;

i.e.,

the

series

path

from

the

emitter

of

emitter-follower

Q4

to

the

base

of

transistor

Q9

is

seen

to

have

a

very

low

impedance.

Since

transistors

Q9

and

QIO

form

a

cascode

emitter

follower,

the

signal

input

at

!•

5-3

2

that

exceeds

the

bios

level

will

now

appear

at

the

collector

of

QIO,

the

output

of

the

cascode

emitter

follower.

The

emitter

of

Q7

is

connected

to

the

wiper

of

the

trimpot,

R29,

labeled

PED

ESTAL.

The

pedestal

is

normally

adjusted

for

a

value

of—100

millivolts,

i.e.,

to

a

negative

voltage

level

that

is

equal

in

magnitude

and

opposite

in

polarity

to

the

discriminator

threshold

of

the

Schmitt

trigger

circuit,

Q1

1

and

Q12.

It

is

important

to

note

that

the

input

signal

to

the

biased

amplifier

must

exceed

the

bias

level

(Vg

)

by

approximately

100

millivolts

before

the

linear

gate,

Q5

and

Q7,

will

be

switched

open.

Since

the

linear

gate

is

either

open

(Q5

saturated)

or

closed

(Q5

back-biased),

there

is

negligible

nonlinearity

for

signals

just

ex

ceeding

the

bias

level.

The

adjustment

of

the

pedestal

trimpot

is

considered

further

in

Section

6.2.

5.2

The

Biased

Amplifier

GAIN

is

of

the

resistor

shunt

type

on

the

output

of

the

cascode

emitter

follower,

Q9

and

QIO.

As

the

amplifier

following

the

cascode

emitter

follower

is

of

the

current

type,

a

shunt

resistor

to

ground

from

12

wil

l

reduce

the

amount

of

current

flowing

into

the

base

of

transistor

Q13

for

a

given

output

voltage

from

the

cascode

emitter

follower.

The

amplifier

loop,

Q13-Q14,

and

the

output

cable

driver

loop

Q15-Q16

Q1

7,

and

Q18,

are

of

the

basic

type

shown

in

Figure

5-1,

with

the

exception

of

the

diode

limiter

in

the

loop

Q13-Q14.

Notice

that

the

diode

limiter

in

the

loop

is

necessary

because

the

output

of

Q9

and

QIO,

the

cascode

emitter

follower,

can

be

equal

to

10

volts

under

the

conditions

of

a

10-volt

input

signal

and

a

bias

level

of

000.

The

output

driver

loop

consists

of

Q15

through

QIB.

Q15

and

Q17

constitute

the

typical

npn-pnp

loop,

and

they

drive quite

well

in

the

negative

direction

but

not

in

the

positive

direction.

The

addition

of

emitter-follower

Q16

in

this

loop

allows

the

overall

loop

to

handle

both

positive

and

negative

signals

quite

easily

to

plus

or

minus

12

volts

into

100

ohms,

but

an

accidental

short

circuit

of

the

output

will

cause

Q16

to

be

destroyed.

For

this

reason,

Q18

was

added

to

protect

Q16.

The

function

of

Q18

is

to

provide

a

method

of

limiting

the

average

current

through

Q16

to

a

value

less

than

that

required

to

destroy

Q16.

Q18

can

supply

large

peak

currents

from

the

collector-capacitor

C24,

and

these

currents

can

flow

directly

through

Q18

and

Q16

and

thence

into

the

load.

In

the

event

of

a

short

circuit

on

the

output,

the

absolute

magnitude

of

current

that

can

be

supplied

through

Q18

and

Q16

from

C24

is

less

than

that

required

to

destroy

either

Q18

or

Q16.

Capacitor

C24

charges

back

to

the

8+

voltage

through

R47

in

the

absence

of

any

input

pulse.

!•

6-1

6.

MAINTENANCE

6.1

Testing

Performance

of

Biased

Amplifier

6.1.1

Introduction

The

following

paragraphs

are

intended

as

an

aid

in

the

installation

and

checkout

of

the

Model

408.

These

instructions

present

information

on

front

panel

controls,

waveforms

at

test

points

and

output

connectors.

6.1.2

Test

Equipment

The

fol

lowing,

or

equivalent,

test

equipment

is

needed:

(1)

ORTEC

Model

419

Pulse

Generator

(2)

Tektronix

Model

580

Series

Oscilloscope

(3)

100-ohm

BNC

terminators

(4)

Vacuum

tube

voltmeter

(5)

ORTEC

Model

410

Multimode

Amplifier

(6)

Schematic

and

block

diagrams

for

Model

408

Biased

Amplifier

6.1.3

Preliminary

Procedures

(1)

Visually

check

module

for

possible

damage

due

to

shipment.

(2)

Connect

ac

power

to

Nuclear

Standard

Bin,

ORTEC

Model

401

/402.

(3)

Plug

module

into

Bin

and

check

for

proper

mechanical

alignment.

(4)

Switch

ac

power

on

and

check

the

dc

power

supply

voltages

at

the

test

points

on

the

Model

401

Power

Supply

control

panel.

6.1.4

Biased

Amplifier

The

threshold

discriminator

and

pedestal

have

been

set

at

the

factory

and

steps

1

through

9

can

be

omitted

in

original

instal

lations.

(1)

Feed

the

output

of

the

Model

419

Pulse

Generator

into

the

input

of

the

Model

410

Amplifier.

(2)

Set

the

amplifier

controls

as

follows:

1

.1

fjLsec

INPUT

ATTENUATOR

COARSE

GAI

N

INTEGRATION

NEG

1.5

D.L.

INPUT

POLARITY

FINE

GAIN

1

st

DIFFERENTIATION

{outer

concentric

control)

D.L.

2nd

DIFFERENTIATION

(inner

concentric

control)

(3)

Adjust

the

Model

419

Pulse

Generator

for

a

300-mV

pulse

from

the

unipolar

output

of

the

Model

410.

(4)

Set

the

Model

408

BIAS

LEVEL

at

000

divisions

and

the

GAIN

to

1.

(5)

Feed

the

300-mV

unipolar

output

of

the

Model

410

into

the

INPUT

of

the

Model

408.

(6)

Adjust

the

trimpot

at

the

front

of

the

Biased

Amplifier

board

fo

the

position

where

an

output

is

observed

at

the

Model

408

output.

(7)

Decrease

the

input

to

the

Model

408,

with

the

Model

419

Pulse

Generator,

to

1

00

mV

while

adjusting

the

front

trimpot

to

keep

an

output

pulse

present

at

the

Model

408

output.

The

amplitude

of

the

output

pulse

at

the

Model

408

output

is

unimportant

for

this

ad-

6-2

justment,

but

the

Model

408

output

should

be

"half-firing"

with

a

100-mV

input

signal.

(8)

Adjust

the

trimpot

in

the

middle

of

the

board

so

that

the

output

pulse

of

the

Model

408

is

approximately

zero

with

a

100-mV

input

signal.

(9)

Switch

the

Biased

Amplifier

GAIN

to

20.

Adjust

the

m/dd/e

trimpot

,

^

"

to

zero

volts

output

with

the

100-mV

input

signal.

0

(10)

Set

the

Biased

Amplifier

GAIN

control

to

1.

(11)

Adjust

the

Model

419

Pulse

Generator

for

a

400-mV

output

from/t^^^-vi^A

/

tUo

AA^.-i^i

/tn£3

ibr

jv

•7

the

Model

408

(12)

Check

that

the

Biased

Amplifier

GAIN

switch

positions

ore

ap

proximately

correct,

i.e.,

1,

2,

5,

10,

20.

(13)

Set

the

GAIN

switch

at

1

and

the

output

from

the

Model

408

to

8.0

volts.

(14)

Load

the

Model

408

OUTPUT

with

a

100-ohm

terminator.

The

out-

(3K

put

amplitude

should

change

less

than

200

mV

and

there

should

be

no

change

in

the

pulse

shape.

(15)

Readjust

the

Model

419

Pulse

Generator

for

on

8.0-volt

output

from

the

Model

408.

(16)

Increase

the

Model

408

BIAS

LEVEL

control

setting

from

000

di

visions

until

the

output

pulse

from

the

Model

408

ceases.

The

set-

ting

of

the

BIAS

LEVEL

control

should

be

820

±

40

divisions.

(17)

Increase

the

BIAS

LEVEL

50

divisions

above

the

setting

found

in

the

Set

the

GAIN

switch

to

20.

(18)

The

feedthrough

as

observed

on

the

Model

408

output

should

be

^

less

than

50

mV.

(19)

Decrease

the

BIAS

LEVEL

control

setting

to

000

divisions,

leaving

the

GAIN

switch

on

20.

(20)

The

Model

408

output

should

saturate

with

an

output

voltage

pulse

greater

than

1 1

volts.

6.2

Biased

Amplifier

Threshold

and

Pedestal

Adjustment

The

Biased

Amplifier

is

normally

closed

to

all

input

signals

less

than

100

mV

above

the

BIAS

LEVEL

control

setting.

The

linear

gate

in

the

Biased

Amplifier

circuitry

is

activated

by

a

trigger

circuit

which

has

an

adjustable

threshold.

The

threshold

is

set

by

the

trimpot,

R22,

on

the

408-148

etched

board.

This

threshold

is

normally

set

at

the

factory

at

100

mV,

but

may

be

varied

from

approximately

50

mV

to

200

mV

if

desired.

The

purpose

of

the

Biased

Amplifier

pedestal

adjustment

is

to

offset

the

100-

mV

threshold;

i.e.,

with

an

input

signal

of

100

mV

above

the

BIAS

LEVEL,

the

Biased

Amplifier

will

pass

this

signal,

but

the

pedestal

is

adjusted

so

that

the

output

from

the

Biased

Amplifier

is

zero

volts.

The

procedure

for

setting

the

threshold

and

pedestal

trimpots

is

found

in

Section

6.1.

Refer

also

to

Section

5

and

see

Drawings

408-0148-Bl

and

408-

0148-Sl.

6.3

Suggestions

for

Troubleshooting

In

situations

where

the

Model

408

is

suspected

of

malfunction,

it

is

essential

to

verify

such

malfunction

in

terms

of

simple

pulse

generator

impulses

at

the

input

and

output.

In

consideration

of

this,

the

Model

408

must

be

disconnected

from

its

position

in

any

system,

and

routine

diagnostic

analysis

performed

with

a

test

pulse

generator

and

oscilloscope.

It

is

imperative

that

testing

not

be

performed

with

a

source

and

detector

until

the

amplifier-biased

amplifier

system

performs

satisfactorily

with

the

test

pulse

generator.

The

testing

instructions

listed

in

Section

6.1

of

this

manual

and

the

circuit

de-

descriptions

in

Section

5

should

provide

assistance

in

locating

the

region

of

trouble

and

repairing

the

malfunction.

The

guide

plate

and

shield

can

be

com

pletely

removed

from

the

module

to

enable

oscilloscope

and

voltmeter

obser

vations

with

a

minimal

chance

of

accidentally

short-circuiting

portions

of

the

etched

board.

The

Model

408

utilizes

the

modular

etched

board

concept

in

that

all

the

active

circuitry

in

the

module

can

be

removed

from

a

plug-in

socket.

This

has

the

advantage

of

servicing

the

unit

by

substitution

of

the

affected

etched

board

either

from

spares

kept

on

hand

or

obtained

from

the

factory.

The

Model

408,

or

the

etched

circuit

board,

may

be

returned

to

ORTEC

for

re

pair

service

at

nominal

cost.

The

standardized

procedure

requires

that

each

repaired

instrument

receive

the

same

extensive

quality

control

tests

that

a

new

instrument

receives.

6.4

Tabulated

Test

Point

Voltages

on

Etched

Board

The

following

voltages

are

intended

to

indicate

the

typical

dc

voltages

mea

sured

on

the

etched

circuit

board.

In

some

cases

the

circuit

will

perform

satis

factorily

even

though,

due

to

component

variations,

there

may

be

some

volt

ages

that

measure

outside

the

given

limits.

Therefore,

the

voltages

given

here

should

not

be

taken

as

absolute

values,

but

rather

are

intended

to

serve

as

an

aid

in

troubleshooting.

Table

6.1

Typical

DC

Voltages

Note:

1.

All

voltages

were

measured

from

ground

with

vtvm

having

input

impedances

of

10

megohms

or

greater,

2.

Voltages

are

dc

values

with

no

input

pulses.

3.

Set

BIAS

LEVEL

to

000

divisions

and

GAIN

switch

to

XI.

Location

1

2

3

4

5

6

7

8

Transistor

No.

and

Elementi.#^#^

011b

Q12e

Voltage

+0.05

-0.5

-12.4

+101

-10.0

-0.08

Limits

-0.06

-0.6

-12.7

+0.95

+0.97

-11.0

+0.08

-0.5

'.

yp^ttr

Location

9

10

11

12

13

Transistor

No.

and

Element^^j^j

q,^,.

3,7^

Q,g|j

Q,g,.

Voltage

IBM

6.8

14.^

1.2

14.2

Ml

#

Limits

Mm

^'lO

BIN/MODULE

CONNECTOR

ASSIGNMENTS

FOR

AEC

STANDARD

NUCLEAR

INSTRUMENT

MODULES

PER

TID-20893

Function

1

+3

volts

23

Reserved

2

—3

volts

24

Reserved

3

Spare

Bus

25

Reserved

4

Reserved

Bus

26

O-30

volts

ac

5

Coaxial

27

0—30

volts

ac

6

Coaxial

*28

+24

volts

7

Coaxial

*29

—24

volts

8

200

volts

dc

30

Spare

Bus

9

200

volts

dc

31

Carry

No.

2

10

+6

volts

*32

Spare

1 1

—6

volts

*33

115

volts

ac

12

Reserved

Bus

*34

Clean

Ground

13

Carry

No.

1

35

Reset

14

Spare

*36

Gate

15

Reserved

37

Spare

*16

+

1

2

volts

38

Coaxial

*17

—

1

2

volts

39

Coaxial

18

Spare

Bus

40

Coaxial

19

Reserved

Bus

*41

1

15

volts

ac

20

Spare

*42

Dirty

Ground

21

Spare

G

Ground

Guide

22

Reserved

*These

pins

are

installed

and

wired

in

parallel

in

the

ORTEC

Model

401

Modular

System

Bin

!•

The

transistor

types

installed

in

your

instrument

may

differ

from

those

shown

in

the

schematic

diagram.

In

such

cases,

necessary

replace

ments

can

be

made

with

either

the

type

shown

in

the

diagram

or

the

type

actually

used

in

the

instrument.

!•

The

transistor

types

installed

in

your

instrument

may

differ

from

those

shown

in

the

schematic

diagram.

In

such

cases,

necessary

replace

ments

can

be

made

with

either

the

type

shown

in

the

diagram

or

the

type

actually

used

in

the

instrument.

ORTEC 408 User manual

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