Datapulse 101 - Circuit Description

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3.2

CIRCUIT

DESCRIPTION

Refer

to

the

schematic

diagram

for the

following

discussions.

3

2.1

Repetition

Rate

Oscillator

The

internal

rate

oscillator

is

an

emitter

coupled

multivibrator

with

high

level

positive

feedback

for

ac

provided

by

the

timing

capacitors

C6

through

Cll.

This

circuit

supplies

a

free-running

basic

rate

that

governs

the

remaining

circuits

and

provides

system

clock

output

pulses.

In

addition,

it

has

the

capability

of

synchronously

starting

oscillations

that

begin

at

the

leading

edge

of

a

control

gate

and

continue

until

the

gate

is

removed.

The

oscillator

circuit

consists

of

transistors

Q2,

Q3,

and

Q4

and

their

related

circuit

components.

To

trace

the

cycle

of

operation,

assume

that

Q4

is

cut

off

and

Q2

is

conducting;

the

waveform

at

the

base

of

Q4

will

then

be

rising

exponentially

toward

ground.

The

emitter

of

Q4

will

be

held

near

ground

by

the

conducting

emitter

of

Q2

and

when

the

base

of

Q4

reaches

ground,

Q2

will

start

to

cut

off.

The

resulting

positive

step

at

the

collector

of

OZ

will

be

transferred

through

emitter

follower

C3

and

the

timing

capacitor

(C6

through

C11)

to

the

base

of

Q4.

QB

provides

a

low

impedance

discharge

path

for

the

timing

capacitor

through

diode

CR3

to

ground.

C4

will

regeneratively

turn

on

while

QZ

is

turned

off

but

the

circuit

will

remain

in

this

condition

for

only

a

short

time

because

of

the

low

impedance

of

CR3.

It

will

again

become

regen-

eratively

unstable

and

Q4

will

be

cut

off

when

the

timing

capacitor

discharges

through

CR3,

starting

the

cycle

over

again.

The

collector

of

Q4

provides

an

isolated

output

that

does

not

affect

the

timing

circuitry

and

is

used

to

drive

the

trigger

multivibrator

(CR50

and

08)

and

the

advance

trigger

amplifier

(Q7).

The

positive

step

at

the

collector

of

Q4,

when

it

is

cut

off

operates

the

trigger

multivibrator

and

the

negative

step,

when

Q4

again

conducts

drives

the

advance

trigger

amplifier.

The

negative

step

always

appears

somewhat

before

the turnoff

of

Q4

and

is

present

whenever

the

rate

oscillator

is

running.

3,

Z.

2

External

Gate

Amplifier

Q1

is

a

buffer

amplifier

stage

which

inverts

the

external

gate

and

provides

the

standardized

output

to

gate

the

rate

oscillator

and

the

delay

multivibrator.

The

base

to

emitter

drop

of

Q1

sets

the

gate

amplitude

requirement

and

base

resistor

R2

provides

input

impedance

as

well

as

protection

from

overdrive.

In

the

asynchronous

gating

mode,

the

output

of

()1

drives

Q9

which

is

used

to

gate the

delay

multivibrator.

The

rate

oscillator

is

not

gated.

In

synchronous

gating,

the

rate

oscillator

is

stopped

at

a

point

in

its

cycle

just

before

the

turn

off

of

Q4

would

normally

Occur

and

is

held

in

this

condition

by

the

current

through

resistor

R4

and

diode

CR1.

The

application

of

a

gate

signal

drives

the

collector

of

Ql

abruptly

negative

and

allows

Q4

to

turn

off

by

stopping

the

current

flow

in

R4

and

CR1

that

was

holding

its

base

3-4

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