IEC 30 Series - Page 23

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Width

control

R2IO

are

summed.

Q50

is

an

out-

put

buffer

for

providing

a

frequency

analog

voltage

to

the

current

control

circuits

and

also

to

IC I 7 which

drives

an

external

frequency

analog

out

connector

(F34

only).

b. CURRENT SOURCES. -

Generation

of two

equal

and

opposite

currents

is

accomplished

by

IC3

and

Q3

for

negative

current,

and

ICI,

IC2,

and

Q2

for

the

positive

current.

The

diode

switching

bridge,

CR3

through

CRIO,

allows

only

one

current

at

a

time

to

be

applied

to

the

integrating

capacitors,

CI

through

CIO. A

volt-

age

level

generated

in

the

VLS

section

selects

the

polarity

of

the

current.

c.

FOLLOW

AMPLIFIER.

-

The

follow

amp

is

a

unity

gain

amplifier

with

extremely

high

input

impedance

that

prevents

integrating

capacitor

loading

which would

result

in a

bowed

triangle

waveform.

LOW-impedance

out-

puts

provide

triangle

waveforms

to

the

system.

The

input

of

the

follow

amp

is

a

JFET

source

follower.

The

Vgs

offset

is

compensated

by

adjusting

R29.

d. VOLTAGE

LEVEL

SENSOR. -

The

voltage

level

sensor

(VLS)

provides

SWitching

signals

to

the

diode

bridge

and

also

generates

low-

impedance

squarewaves

of

controlled

ampli-

tude

to

the

output

amplifier

and

logic

sections.

The

rising

triangle

voltage

level

present

at

the

follow

amplifier

output

is

compared

with

a

reference

voltage

at

the

input

to

the

differential

comparator,

IC5. When

the

follow

amplifier

output

reaches

the

reference

voltage,

IC5

changes

state

producing

a

signal

which

is

fed

back

to

the

diode

bridge

(CR3

through

CRIO)

in

the

current

amplifier.

It

also

produces

a

new

reference

comparison

voltage

at

pin

4 of IC5

which

generates

the

reqUired

hysteresis.

Ad-

justments

R5I

and

R54

enable

the

reference

SECTION

3

voltage

to

be

set

up

so

that

a

symmetrical

waveform

is

produced.

Q7

and

Q8

form

a

complementary

emitter

follower

with

low-output

impedance.

This

output

is

the

squarewave

function

which

may

be

se-

lected

by

the

waveform

switch.

R63

provides

an

adjustment

for

the

d-c

level

(amplitude

sym-

metry)

of

the

squarewave

output.

Q5I

(F33,

F34) prOVides a

means

of

shifting

the

VLS

reference

level

approximately

I

percent.

When

an

external

repetitive

waveform

is

applied

at

the

Trigger/Sync

connector,

Q5I

serves

to

advance

the

VLS

switching

point

and

thus

ob-

tain

synchronous

operation.

e.

START/STOP

CONTROL

(F33,

F340nly).-

This

circuit

forms

a

three-element

gate

whose

inputs

are

two

logic

levels

and

one

analog

level.

When a

stop

command

level

is

present

and

the

VLS

square

wave

signal

indicates

that

the

tri-

angle

is

negative

going,

the

output

of

the

follow

amplifier

is

compared

to

a

reference

level

(zero

volts).

When

the

triangle

voltage

reaches

this

reference,

the

Start/Stop

Amplifier

becomes

active

and

causes

the

integrating

capacitor

charging

current

to

be

bypassed

from

the

capacitors

through

CR58,

thereby

clamping

the

voltage

of

the

triangle

waveform

to

the

reference.

When

the

stop

command

ceases,

the

integration

process

resumes

as

the

Start/Stop

Amplifier

is

deactivated

and

CR58

is

reverse

biased.

3-4.

SINE

SHAPER

Sinewaves

are

produced

by

shaping

the

tri-

angle

waveform

with

shunt

diode-resistor

net-

works.

Integrated

circuits

IC7

and

IC8

con-

tain

matched

diode

sets

which,

in

series

with

R74

resistor

elements,

load

the

triangle

and

3-3

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