AD8389 Просмотр технического описания (PDF) - Analog Devices

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AD8389

Triple, 6-Channel LCD Timing Delay-Locked Loop

Analog Devices 

AD8389

OPERATING PRINCIPLES

DX

CLX,

ENBX(1–4)

200pF

MONITRI

DXI

DXRO

CLXRO,

ENBX(1–4)O

VCONTR

AD8389

MONITO

MONITI

DXI

CLXIN,

ENBX(1–4)I

DXO

CLXO,

ENBX(1–4)O

AD8384/AD8385

LEVEL SHIFTER SECTION

MON

H SHIFT

REGISTER

RED LCD

Figure 6. AD8389 Application in the Red Channel of an LCD Projection System

The image quality of an LCD system is dependent on the timing

relationship between the control inputs, DX, CLX, ENBX(1–4),

and the video channels.

TFT delay and switching speed variations, due to temperature

variations and LCD aging, degrade image quality if not

compensated.

An internal reference TFT connected to an internal pull-up

resistor, as shown in Figure 6, characterizes the internal S/H

TFTs of the LCD and monitors switching speed and delay

variations due to aging and temperature. When the MON

output of an LCD that includes such an internal reference TFT

is connected to the reference input of the AD8389 delay-locked

timing loop, continuously optimized timing of the LCD is

maintained automatically.

OPERATION

As part of a closed loop, the AD8389 maintains a constant delay

between the common input, DXI, and each independent

feedback reference, MONITxI. The block diagram of such

closed-loop system is shown in Figure 6.

A constant delay, t7, selected via the COMPEDGE and SLOW

control inputs, is applied to the DXI input to approximate the

nominal, initially expected total delay, t7, through the level

shifters and the LCD as shown in Table 5.

Table 5

COMPEDGE

1

1

SLOW

0

1

Constant Delay

15/fCLK + t4 DX

CONSTANT

9/fCLK + t4

MONITRI

0

0

32/fCLK + t4

CONSTANT

0

1

26/fCLK + t4 DX

MONITRI

Rev. 0 | Page 7 of 12

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