1.Comparison between TN, STN and FSTN technologies.
2.Differences between reflective, transflective and transmissive displays.
3.Reference to Viewing angle.
4.Clarification to the term "rainbow" effect.
5.The minimum dot size and pitch on the LCD, the ITO line on the LCD and the elastomer (zebra) connector.
6.Adjusting the contrast of a character LCD module.
7.Advantages and disadvantages of backlight versions.
8.Connecting and powering the backlight.
9.Controlling the LED backlight on a 14-pin module.
10.Differences between a Driver IC, a Controller IC and a Controller/Driver IC.
11.Considerations for attaining a 3.0 Volt LCD module.
12.Pin assignments for a Character module.
13.What is temperature compensation and why is required?
14.Troubleshooting an LED backlight module in which the display is turning dark.
15.Brief description of various controller IC's.
16.Following is the Vop range for a Character and Graphics LCD module.

1.Comparison between TN, HTN, STN and FSTN technologies:

ITEM	Contrast Ratio	View Angle	COST
TN	1	1	1
HTN	2	2	2
STN	3	3	3
FSTN	4	4	4

Remarks: with 4 being the best or most expensive and 1 the worst or least expensive

 

2.Differences between reflective, transflective and transmissive displays?

Reflective: Such display includes a diffuser. This layer reflects the light that enters the front of the display. Reflective displays require ambient light for the light source since there is no backlight.

Transflective: As type of backing which is bonded to the rear polarizer. Enables light to pass through the back, as well as reflecting light from the front.

Transmissive: A type of LCD which does not have a reflector or transflector laminated to the rear polarizer. A backlight must be used with this type of LCD configuration. The most common is a transmissive negative image.

 

3.Reference to Viewing angle:

Viewing Angle is the direction by which the display will look best. This is established during the manufacturing process and can not be changed by rotating the polarizer. Viewing direction is specified in terms of a clock position, such as 6:00 & 12:00. Please refer to the following drawing:

This refers to a red and green circle or rainbow on the LCD glass. The LCD panel under uneven pressure causes this problem from the bezel. This problem is very common in LCD modules and normally it will not affect the performance or the appearance of the display when operational.

 

5.Following is the minimum dot size and pitch on the LCD, the ITO line on the LCD and the elastomer (zebra) connector:

Item	Dots or Lines	Gaps
LCD Dots	0.22mm	0.02mm
LCD ITO lines	S=0.075, C=0.08mm	0.03mm
Rubber Connectors	0.025mm	0.025mm
Heat Seal	0.09mm	0.09mm

 

6.Adjusting the contrast of a character LCD module.

There are two means of adjusting the contrast: Please refer to the following drawing:

Internal: J2 short, add the appropriate resister to R7 for contrast control.
External: J1 short, R7=0, By adding a VR the contrast can be controlled externally. Please note the following diagram

 

7.Advantages and disadvantages of backlight versions:

ITEM	LED	EL	CCFL
Type	Edge & Array	Thin Flat Panel	Direct & edge lighting
Power Requirement	DC 4.2V, Hight power consumption in array type	AC 110～130V, 400Hz, need DC/AC converter, Low power consumption	AC 600～1000V, 30KHz, Need DC/AC converter, Low power consumption
Brightness	15～80 CD/square M	70～200 CD/square M	200～600 CD/square M
Life	50,000～100,000hr	2,000～5,000hr	10,000～20,000hr
Thickness	Array: 5mm Edge: 1.3～4mm	1.5mm Max	Direct: 15.0mm Edge: 3.0mm
Color	Yellow/Green, Green,Amber, Red, Orange	Blue/Green, Yellow/Green, White	White

 

8.Connecting and powering the backlight.

There are two means of connecting and powering the backlight. Please refer to the below diagrams:

1. PINS 1 & 2 (Vdd & Vss): J3 short, by adding a resistor on R9.
2. PINS 15 & 16: J4 short, by adding a resistor on R8.

NOTE: The brightness can be controlled by the value of R8 or R9.

 

9.Controlling the LED backlight on a 14-pin module:

Short J2, the Vdd is controlling the input to the LED backlight. In addition, it is necessary to place a current limiting resistor to lower the voltage from 5V to 4.2V.

Note: If the LED is drawing too much current it may cause the Vdd–Vo to lower and the contrast to become poor. If this should occur increasing the value of R9 should decrease the current draw to the LED backlight or another approach would be to increase the voltage input to the LCD by decreasing the value of R7

Driver IC: There are two types of driver IC's. One is a "common" driver and the other a "segment" driver. Common drivers output signals to create the rows or number of lines while the segment drivers output the necessary signals to create the characters or columns.

Controller IC: This IC receives data written in ASCII or JIS code from the MPU and stores this data in RAM. This data is then converted into a serial character pattern and transferred to the LCD driver IC.

Driver/Controller IC: This IC is most commonly found in a graphics module. This IC receives data from the MPU and stores it in RAM. This IC accepts commands directly from the MPU for both the common and segment drivers.

11.Considerations for attaining a 3.0 Volt LCD module:

IC: Choose the ICs that can be driven at 3.3V or less. Below is a list of IC's that can accomplish this requirement:

Controller:

KS0066U 2.7 ~ 5.5V
KS0070B 2.7 ~ 5.5V
HD44780U 2.7 ~ 5.5V

Driver:

KS0065 2.7 ~ 5.5V
KS0063 2.7 ~ 5.5V
SED1181 5.0V min.

LCD panel: The driving voltage for most all LCD panels is above 3.3V. It is necessary to then add a "negative voltage" IC on the PCB of the module or to the customer's motherboard to raise the voltage. A couple of NV generators is as follows:

NV IC: SCI7661 3X with temperature compensation.
SCI7660 2X, dice font available (at a much less expensive cost).

If a NV IC must be incorporated onto the module PCB, there is apt to be two possible considerations:

1. Tooling cost

2. The PCB is too small to accommodate the NV IC. If there is not sufficient space, a possible solution would be to replace one controller with a driver, with single controller (such as replacing a KS0066(U) & KS0065(B) with a KS0070). The per unit cost will be a little greater but it will save overall space on the PCB and eliminate having to re-tool the PCB.

Some TAB IC"s such as SED1560 series include a power circuit, which can amplify the input voltage to drive the LCD. In this case it is not necessary to add a NV IC to raise the voltage.

C.Backlight:

CCFL & EL: These backlight options require an inverter. The inverter that is chosen cannot exceed 3.3 Volts.

LED: In an attempt to achieve this 3.3V requirement it is necessary to use an edge-lit LED. Note: This edge-lit LED will still consume a large current.

Example of a standard 14-pin character module:

PIN 1: Vss
PIN 2: Vdd
PIN 3: Vo
PIN 4: RS
PIN 5: R/W
PIN 6: Enable
PIN 7 ~ 14: DB0 ~ DB7

 

A LCD operating voltage varies at different temperatures. The operating voltage must rise as temperature lowers or the contrast will degrade. Conversely, the operating voltage must fall as the temperature rises or the contrast will degrade. For this reason it is often a requirement, with graphics modules, to control the input voltage accordingly. The temperature compensation circuit is the circuit that controls the input voltage as the temperature changes. This temperature compensation circuit can be located on the LCD module or on the customer's motherboard.

 

This problem is more than likely caused by the temperature rise from the LED backlight. In this case the LED backlight has consumed too much of the power. When the temperature rises, the V_LCD requirements lower causing the input voltage to be too high. The result is a poor contrast and the display becoming too dark. The solution would be to lower the power consumption of the LED. This can be accomplished by raising the value of R8 or R9 to reduce the current to the LED backlight.

15.Brief description of various controller IC's:

Font Number	IC Number	Temp. Range	Content
SO	KS0066	Wide	English/Japanese
EA	SED1278	Normal	English/Japanese
S5	KS0066	Wide	English/Europe
EB	SED1278	Normal	English/Europe

 

16.Following is the Vop range for a Character and Graphics LCD module:

Note: N.T. = normal temperature
W.T.= wide temperature