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LCD Electronics Theory of Operation Dick McCartney Corporate Technologist 1 Feb 2010 LCD Functional Diagram Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver W-LED RGB-LED Light Source Backlight PWR Conv

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slide1

LCD Electronics

Theory of Operation

Dick McCartney

Corporate Technologist

1

Feb 2010

lcd functional diagram
LCD Functional Diagram

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

slide3

Ernst Lueder, "Liquid Crystal Displays : Addressing Schemes and Electro-Optical Effects (Wiley Series in Display Technology)", John Wiley & Sons, 22 June, 2001.

liquid crystal nematic order

free

az

bound

free

free

ax

director axis

bound

free

ay

Liquid Crystal Nematic Order

Nematic Order:

  • Free to translate in x,y and z directions
  • Free to rotate about the major (director) axis
  • Restricted rotation of the director axis
dielectrics of nematic order
Dielectrics of Nematic Order

Dielectric Property

eperpendicular-2

eperpendicular

eparallel

eparallel

eperpendicular-1

director axis

director axis

Nematic Order reduces a 3-dimensional dielectric property to two dimensions.

eperpendicular-1

eperpendicular-2

+

eperpendicular

Due to spin about the director axis.

=

2

torque depends on v rms
Torque Depends on VRMS

RMS dependency

Temperature dependency

dielectric anisotropy

order depend on springs
Order Depend on Springs

Nematic order is maintained by intermolecular forces which are macroscopically characterized as spring constants for the material.

The bend, twist and splayspring constants restore order in a perturbed system. E-field inducted torque works against these springs.

The spring constants also depend on temperature

lcd monitor block diagram
LCD Monitor Block Diagram

Display

Electronics

Scaler

RGB (VGA)

DVI

Power

Converter

Backlight

WALL PWR

L

Audio

AMP

AUDIO IN

R

lcd tv block diagram
LCD TV Block Diagram

Display

Electronics

Tuner

Video

Processor

CABLE

CVBS

Y/C

YUV

YPbPr

Power

Converter

RGB (VGA)

DVI/HDMI

Backlight

WALL PWR

L

Audio

AMP

Audio

Processor

AUDIO IN

AUDIO OUT

R

representative smart phone system
RepresentativeSmart Phone System

Radio Section

Including:

carrier modem,

Bluetooth, WiFi, GPS

PMU

LED

Driver

Application

Processor

Key

pad

Key

Pad

Cntlr

Level

Shifter

Memory

Stick

Battery

Charging &

Protection

Processor/

Main Unit

Camera

LED

Driver

LED

Flash

Display

Audio

Subsystem

Micro-

phone

Display Driver

& Power

Audio

Amplifier

Audio/Video

ltps lcd functional diagram
LTPS LCD Functional Diagram

Display

Driver Chip

Timing

Controller

Application Processor

or Graphic Controller

DSI

MPL

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

Integrated into the LTPS display panel

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

lcd device operation
LCD Device Operation

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

CCFL

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

active matrix
Active Matrix

source or column driver

(row)

gate

NMOS

FET

source

drain

(column)

(subpixel)

gate or row driver

common

backplane driver (Vcom)

serial data scan pattern converted to row by row
Serial Data Scan Pattern Converted to Row-by-Row

pixel 1

Serial input R:G:B

new frame

old frame

v com function
Vcom Function

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

CCFL

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

gate line charge injection
Gate Line Charge Injection

Gate bus

Cgd

Cstore

Clc

alternating voltage drive

V

Alternating Voltage Drive

Normally-White

Operation

Alternating polarity is used to keep the average voltage value across the LC at zero. This prevents electroplating of ion impurities in the liquid crystal onto the electrodes. Electroplating of contaminants is a major source of image retention (sticking image).

Brightness

RMS Voltage

subpixel voltage translation
Subpixel Voltage Translation

Gate Bus Voltage

Subpixel

Voltage

DV

+ Polarity

Translated Source Bus Voltage

DV

- Polarity

Row

Select

Time

v com equivalent circuit at the subpixel level
Vcom Equivalent Circuit at the Subpixel Level

real transistor with its charge injection modeled as a series voltage drop.

ideal transistor without charge injection operating as a voltage controlled switch.

V

Vsource

Vsource

Vgate

Vgate

Clc

Cstore

Clc

Cstore

Vcom

static and dynamic vcom
Static and Dynamic Vcom

Cgd

Vsource

Clc

Vgate

Cstore

Vcom dynamic(GL)

Vcom static

grayscale dependent offset
Grayscale Dependent Offset

Cgd

Column Driver

Vsource

Clc

Vgate

Cstore

Vcom dynamic (GL)

Vcom static

adding dynamic v com to each gray level of the column driver
Adding Dynamic Vcom to each gray level of the Column Driver

Voltage pair for one particular gray level

normally black

behavior

offset

+V

Dynamic Range

-V

GL

255

0

255

0

GL

Asymmetric

Inverse Gamma Curve

Correcting for DV

Symmetric

Inverse Gamma Curve

corrected matrix

Vcom (GL)

Vcom (GL)

Vcom (GL)

V

V

V

Vcom

Corrected Matrix

V(GL)

V(GL)

V(GL)

Vgate

Clc

Clc

Cstore

Cstore

Clc

Cstore

Vcom

column line or source bus

row driver operation
Row Driver Operation

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

CCFL

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

gate and source voltages
Gate and Source Voltages

Select

Voltage

Gate Bus Voltage

ON

Center of the driving waveform

Valid Source

Bus Range

OFF

De-Select

Voltage

Row Select Time

row driver block diagram

D

D

D

D

D

D

D

D

Q

Q

Q

Q

Q

Q

Q

Q

LS

LS

LS

LS

LS

LS

LS

LS

Row Driver Block Diagram

Start

Out

Start in

CLK

OE

Outputs

amlcd address signal propagation
AMLCD Address Signal Propagation

Column Drivers

Row Signal Delay

Worst Corner

(column driver changes immediately but row fall is delayed)

Row Signal Delay

Column Delay

Column Delay

Column Delay

Row Drivers

Row Signal Delay

Best Corner

(column line changes well after row line changes)

required row select pulse for both near and far column

OE

Required Row Select Pulse for both Near and Far Column

row line signal

column line signal

TFT off

Far column

conventional solution
Conventional Solution

Row and Column Signals

OE

adjustable

width

Row N

Row N + 1

Row N + 2

Row N + 3

Line N

Line N+1

Line N+2

Line N+3

column driver operation
Column Driver Operation

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

CCFL

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

simplified 6 bit 64 1 r dac
Simplified, 6-bit (64:1), R-DAC

analog

voltage

references

Analog output

Gray level voltage

digital

code

(input)

column driver block diagram

Decoder

Decoder

Decoder

Decoder

Column Driver Block Diagram

gamma references

in large format drivers there are two separate banks of reference busses, one for each polarity.

in small format drivers the reference busses are usually shared between polarities.

Digital Gray Levels

Output Strobe

Outputs

direct drive column driver

Column Driver

Direct Drive Column Driver

Column Driver

Row Driver

Vcom

Driver

direct drive column driver34

Column Driver

Direct Drive Column Driver

Column Driver

Row Driver

Vcom

Driver

v com modulation inverse gamma
Vcom Modulation Inverse Gamma

Negative

Positive

Graylevel

ltps active matrix
LTPS Active Matrix

LTPS

Display Driver

multiplexer

integrated into glass

gate or row driver integrated into glass

rotated ltps active matrix
Rotated, LTPS Active Matrix

LTPS

Display Driver

rotation permits fewer column outputs for the same

h x v format

frame inversion

Frame M+1

Frame M

E

O

E

O

E

O

E

O

Rows

E

+

+

+

+

E

-

-

-

-

O

+

+

+

+

O

-

-

-

-

E

+

+

+

+

E

-

-

-

-

O

+

+

+

+

O

-

-

-

-

-

-

+

+

Frame Inversion
  • Low Power Operation
  • Sensitive to Flicker Due to Lack of spatial Averaging and Slight Transmissivity Mismatches for + and - Polarities
  • Sensitive to Horizontal and Vertical Cross-talk
line inversion

Frame M+1

Frame M

E

O

E

O

E

O

E

O

Rows

E

+

+

+

+

E

-

-

-

-

O

-

-

-

-

O

+

+

+

+

E

+

+

+

+

E

-

-

-

-

O

-

-

-

-

O

+

+

+

+

-

+

-

+

Line Inversion
  • Reduced Flicker Due to Spatial Averaging
  • Reduced Vertical Cross-talk
  • Compatible with Vcom Modulation Scheme
  • High Power Operation: 480X Higher Power than Frame or Column Inversion
  • Sensitive to Horizontal Cross-talk
column inversion

Frame M+1

Frame M

E

O

E

O

E

O

E

O

Rows

E

+

-

+

-

E

-

+

-

+

O

+

-

+

-

O

-

+

-

+

E

+

-

+

-

E

-

+

-

+

-

-

+

+

O

+

-

+

-

O

-

+

-

+

Column Inversion
  • Low Power Operation
  • Further Flicker Reduction Due to Spatial Averaging
  • Greatly Reduced Horizontal Cross-talk
  • Requires High Voltage Source Driver
  • Reduces component count and complexity
  • Incompatible with Vcom Modulation
pixel inversion

Frame M+1

Frame M

E

O

E

O

E

O

E

O

Rows

E

+

-

+

-

E

-

+

-

+

O

-

+

-

+

O

+

-

+

-

E

+

-

+

-

E

-

+

-

+

O

-

+

-

+

O

+

-

+

-

-

+

-

+

Pixel Inversion
  • Highest Quality Image Due to Reduction in Both Horizontal and Vertical Cross-talk
  • No Flicker Due to Spatial Averaging
  • Requires High Voltage Source Driver
  • Incompatible with Vcom Modulation
  • Higher Power Due to Line Inversion Component
pixel inversion45
Pixel Inversion

Frame 1

+

-

+

-

+

-

-

+

-

+

-

+

-

+

-

+

-

+

Frame 2

+

-

+

-

+

-

n line inversion n 2
N-Line Inversion (N=2)

Frame 1

+

-

+

-

+

-

+

-

+

-

+

-

-

+

-

+

-

+

Frame 2

-

+

-

+

-

+

slide47

ó

ó

ó

l

l

l

l

l

l

P(

P(

)

)

f

f

(

(

) d

) d

K

ó

ó

ó

y

y

Video System Intensity Transformations

(Gamma)

Irradiance

from source (spectral density function)

(watts/steradian)

Simultaneous contrast

Effect in dark surround

= (x)1/125

CRT or other

display device = (x)2.5

Human

Lightness

Perception

(Brightness)

Contrast boost as

Pre-correction for

Dark surround

(assumed = (x)1/1.125

Pre-correction for

display device

(assumed = (x)2,5

(Y)

L

(Y’)

L0.45

(L0.4)

L1.125

L

(x)2.5

(x)1/1.125

(x)1/2.5

116(x/xn)0.33 -16

(x)1.125

P(l)

Camera (video source)

TV Display

Human Visual System

These two spaces are reasonably linear with each other. Enough so that image processing in the Luma domain is close enough to be uniform in perception.

www.poynton.com

Charles Poynton, A Technical Introduction to Digital Video. New York:

Wiley, 1996.

advanced features
Advanced Features

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

CCFL

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

dynamic contrast expansion
Dynamic Contrast Expansion

Reduced

Backlight

(x1/N)

LCD

limited

contrast

Bright

Images

Amplified

Grayscale

(xN)

Dark

Image

When the

Image is

Dark…

Ideal

Contrast

Scale the

Transmission

up by N

Dark

Images

While scaling

The Backlight

Down by N

Ideal

Contrast

Experience

reviewed operations
Reviewed Operations

Timing

Controller

Video Source

Gamma DAC Ref

Column Drivers

Electronics

DC/DC Conv

Display

Vcom

Buffer

Row Driver

W-LED

RGB-LED

Light Source

Backlight

PWR Conv

Controller

Driver

summary of lcd electronics
Summary of LCD Electronics
  • LCD operation is essentially the same across applications
  • Different driving strategies and tactics are used in different applications
  • Different back-lighting strategies are used in each application
  • Innovation and technology advancement continue to extend the size, format, contrast, color performance and portability of LCDs moving them into whole category of products