Datapulse 101 - Page 23

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3.2.

12

Output

Driver

and

Amplifier

Circuits

The

driver

circuits

which

consist

of

transistors

015

through

Q18

are

essentially

overdriven

amplifiers

which

contain

diodes

to

aid

in

the

prevention

of

stored

charge

effects.

The

output

amplifiers

019

through

C22

are

emitter

followers

which

have

their

currents

applied

through

decoupling

networks

whose

impedance

is

constant

with

frequency.

This

helps

to

reduce

tilt

of

the

output

due

to

low

collector

voltages

reflecting

through

to

the

emitter.

Diodes

CRllo

and

CRlll

form

a

Baker

Clamp

to

aid

the

recovery

of

Q16.

Diode

CR112

holds

the

bases

of

019

and

QZO

slightly

below

ground

to

slice

off

small

baseline

irregularities

prior

to

the

leading

edge

of

the

pulse.

Constant

impedance

bridge

"T"

attenuators

connect

the

output

transistors

to

the

output

terminals.

The

positive

going

signal

applied

to

the

base

of

015

by

the

width

multivibrator

turns

Q15

on.

The

current

in

015

turns

Q16

on

and

drives

the

bases

of

Q19

and

Q20

positive

causing

them

to

turn

on.

The

resulting

positive

pulse

at

the

emitters

of

019

and

Q20

is

applied

to

the

positive

output

through

a

variable

attenuator

network

which

provides

output

amplitude

control.

The

emitter

current

of

015

is

taken

by

the

grounded

base

stage

Q17

to

the

negative

pulse

driver

018.

018

is

turned

on

and

diode

CR131

helps

reduce

stored

charge

effects.

The

collector

of

018

and

the

base

of

the

output

transistors

are

held

slightly

above

ground

by

the

current

through

CR132.

This

helps

remove

irregularities

from

the

baseline

for the

negative

pulse.

The

negative

output

is

supplied

by

emitter

followers

Q21

and

Q22

through

its

variable

attenuator.

3.2.

13

Power

Supplies

The

current

required

by

the

output

stages

varies

considerably

with

duty

factor

and

is

measured

in

the

power

supply

by

a.

pair

of

overload

protection

transistors

028

and

Q29.

When

the

drop

across

the

current

sensing

resistors

reaches

approximately

the

base

to

emitter

voltage

of

the

transistors,

a

signal

is

fed

to

the

regulators

shutting

down

the

power

supply

and

preventing

the

output

transistors

from

being

overloaded.

The remainder

of

the

power

supply

is

a

straightforward

regulator

consisting

of

a

simple

pass

transistor

error

amplifier

and

zener

reference

diode.

The

positive

and

negative

12

volt

supplies

are

essentially

identical

and

the

+6

volts

is

provided

by

a

single

emitter

follower

referenced

to

zener

diode

CR507.

3-8

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