ViewSonic VP150M Service Manual - Page 36

ViewSonic

September

2000

-

Version

1.0

Service

Manual

VP150m

THEORY

OF

CIRCUIT

OPERATION

The

detection

logic

is

always

active

to

automatically

detect

any

changes

to

the

input

Mode.

Users

can

manually

change

the

input

mode

information

at

run

time

through

the

CPU

interface.

Detailed

operation

of

the

CPU

interface

is

described

in

Section

3.6

of

"CPU

Interface".

Mode

detection

and

frequency

detection

can

be

independently

turned

ON

or

OFF

by

the

external

CPU.

This

feature

allows

system

customers

to

have

better

control

of

the

mode

-detection

and

frequency

detection

process.

When

the

detection

is

turned

OFF,

the

external

CPU

can

change

the

input

mode

and

frequency

definitions.

Phase

calibration

The

AM101-1

can

automatically

calibrate

the

phase

of

the

sample

clock

in

order

to

preserve

the

bandwidth

of

the

input

signal

and

to

get

the

best

quality.

The

AM101-

1

implements

a

proprietary

image

quality

function.

During

the

auto

-calibration

process,

the

AM101-1

continues

to

search

for

the

best

phase

to

optimize

the

image

quality.

The

output

image

may

display

some

jitter

and

blurring

during

the

auto

-calibration

process,

and

the

image

will

become

crisp

and

sharp

once

the

optimum

phase

is

found.

User

can

change

the

sampling

clock

phase

value

through

the

external

CPU.

Detailed

operation

of

the

CPU

interface

is

described

in

Section

3.6

of

"CPU

Interface".

The

phase

calibration

process

can

be

delayed

and

even

disabled

by

the

external

CPU

if

the

system

designer

wants

to

have

his/her

own

implementation.

The

phase

calibration

can

be

independently

turned

ON

or

OFF

by

the

external

CPU.

PWM

operation

The

AM101-1

implements

a

unique

algorithm

to

adjust

the

phase

of

the

AID

converter's

sampling

clock.

An

external

delay

circuit

is

required

to

compliment

the

AM101-1

for

the

phase

-calibration

process.

The

AM101-1

generates

a

Pulse

-

Width

Modulated

(PWM)

signal

to

the

external

delay

circuit.

The

delay

circuit

should

insert

a

certain

amount

of

time

delay

synchronization

pulse

based

upon

the

width

of

the

PWM

signal.

Confidential

—

Do

Not

Copy

Page

35

ViewSonic VP150M Service Manual - Page 36

ViewSonic, Service, Manual, THEORY, CIRCUIT, OPERATION

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