Epson L90P - TM Two-color Thermal Line Printer Manual do Utilizador descarregar pdf (Página 87)

L

r -

GND

50pF

L

R3

IOK

LI

CC

/250p3

{\

--vWJVNP

RI

2.5 MEG.

_ DI

CI MIMI IN34A

365

pF

C5

.OIyF

R4

4 7K

4J_

5K

t C3

IOyF

Li9

Fig.

2. In

this two- transistor receiver

circuit, regenerative

feedback

is used in Q1 portion

of

the

circuit

while Q2

serves as a capacitively coupled

audio

amplifier. Use 2000 -ohm phones.

nais are

picked up by

a pair of modi-

fied

short-wave receivers and

converted, af-

ter amplification,

into d.c.

signals large

enough

to

operate

an

X -Y

recorder.

A con-

tinuous

curve

is

plotted showing

the

im-

purity

densities at all depths

within the

wafer.

A typical graph

can be seen in

Fig.

1.

Impurity

densities

through the wafer

can

be

plotted

at each point where a metal

dot

has been deposited.

The Profilometer

can measure impurity

densities

as low as one atom in

one billion

over distances

as small

as one ten -thou-

sandth of an inch, or, for impurity

densities

as high as ten

atoms per million, over

dis-

tances

as

small as one

millionth of an

inch. In

coming months,

the new instru-

ment may be used by

a number

of semi-

conductor

manufacturers to insure

the

quality

of their products.

Reader's

Circuit.

Submitted

by reader

James

F.

Kaminski

(23

Fairmeadow

Road,

Wilmington,

Mass.

01887), the

AM broad-

cast -band

receiver

shown in

Fig.

2 should

make an

excellent

"one- evening"

project

for

the beginner or student. James

writes

that

he developed the

circuit by

combining

and

modifying features found

in

several

other

designs. He built

the unit

as part

of

his

work for a Radio

Merit Badge

as an

Eagle

Scout.

Referring

to the

schematic, diode

Dl

and

pnp

transistor QI

work together as a re-

generative*

amplifier /detector

stage while

a second pnp unit,

Q2, serves as a capaci-

tively

coupled audio

amplifier. In

operation,

r.f.

signals picked up by

the

antenna

sys-

tem are selected by

tuned circuit LI -Cl

and coupled

through capacitor

C2

to

DI

and Ql.

Detector -stage base bias is sup-

plied

through 121 and

stabilized

by

emit-

ter resistor

R2, bypassed by

C3. Regenera-

tive r.f. feedback is

furnished by

coil L2,

shunted by regeneration

control

R3. The

detected audio

signal developed across

Ql's

collector load resistor,

R4,

is

coupled

to the

audio stage, Q2,

through C4,

with C5 serving

as

an

r.f. bypass to

minimize the

load's

effect

on

regenerative

circuit action.

Con-

ventional

2000 -ohm magnetic earphones

are

used for

the output.

James has

specified inexpensive,

readily

available parts in

his circuit.

Transistors

QI

and Q2

are

general

purpose pnp

units,

such as types

2N107, 2N404, or

2N1305.

A

standard broadcast

-band, ferrite

coil is

used

for Ll, while L2 consists

of 7 turns

of any

thin insulated wire (size

22 to

30).

L2

is

wound directly on, or

alongside,

LI, de-

pending on

the latter's size and form.

In

common with the majority of

simple

receiver circuits,

neither

parts

arrangement

*See the Transitips

section of

Solid State,

POPULAR

ELECTRONICS.

November, 1968

for a

discussion of

regenerative

circuits.

April,

1969

95

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