ViewSonic VA550 Service Manual - Page 19

ViewSonic

Corporation

Service

Manual

VA550

THEORY

OF

CIRCUIT

OPERATION

AM100

The

AM100

is

capable

of

performing

automatic

detection

of

the

display

resolution

and

timing

of

the

input

signals

generated

from

various

graphic

cards.

The

AM100

then

automatically

scales

the

input

image

to

fill

the

full

screen

of

the

LCD

monitor.

The

AM100

can

interface

with

TFT

LCD

panels

from

various

manufacturers

by

generating

48

-bits

R.G.B.

signal

to

the

LCD

panel

based

upon

the

timing

parameter

saved

in

the

EEPROM

(IC07).

The

AM100

has

the

following

major

functions;

1.

Input

mode

detection.

2.

Auto

calibration.

3.

Image

scaling.

4.

Image

interpolation

and

dithering.

5.

OSD

mixer.

The

following

sections

describe

these

functions:

Input

Mode

Detection

The

AM100

can

automatically

detect

the

mode

of

the

input

signal

without

any

user

adjustment

or

driver

running

on

the

PC

host

or

external

CPU.

It

automatically

detects

polarity

of

input

synchronization

and

the

sizes

of

back

porch,

valid

data

window

and

the

synchronization

pulse

width

in

both

vertical

and

horizontal

directions.

The

size

information

is

then

used

not

only

to

determine

the

input

resolution

to

generate

the

frequency

driver

for

the

input

PLL

to

lock

with

HSYNC,

but

also

to

automatically

scale

the

image

to

full

screen

and

to

synchronize

the

output

signal

with

the

input

signal.

The

detection

logic

is

always

active

to

automatically

detect

any

changes

to

the

input

mode.

Auto

calibration

The

AM100

can

automatically

calibrate

the

phase

of

the

sample

clock

in

order

to

preserve

the

bandwidth

of

input

signal

and

get

the

best

quality.

The

AM100

implements

a

proprietary

image

quality

function.

During

auto

-calibration

process,

the

AM100

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,

but

the

image

will

become

crisp

and

sharp

once

the

optimum

phase

is

found.

User

can

change

the

sampling

clock

phase

value

with

the

external

CPU.

The

phase

calibration

process

can

be

delayed

and

even

disabled

by

the

external

CPU

if

system

designer

wants

to

have

their

own

implementation.

The

phase

calibration

can

be

independently

turned

ON

or

OFF

by

external

CPU.

When

the

calibration

is

turned

OFF,

external

CPU

can

change

the

input

mode

and

frequency

definitions.

CONFIDENTIAL

—

DO

NOT

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