Can you put a touch panel on any display?
What is the difference between transmissive and Transflective displays?
Transmissive: The transmissive liquid crystal cell does not have reflective properties. Utilizing a backlight behind the display creates the image that is displayed on the screen, and the transmissive liquid crystal cell acts as a light valve to either allow the light to pass through the display or to block the light. This technology is used when there are few ambient light sources available.
Transflective: Utilizing a transflector, which is a reflector that will still allow some light to pass through, transflective LCD displays are able to achieve both reflective and transmissive properties. This capability enables acceptable transmissive performance with a backlight in low-light conditions, and allows the utilization of a reflective lower-power mode in adequate ambient light conditions while maintaining good performance in direct sunlight. The transflective viewing mode is the most common monochrome LCD viewing mode.
What is a capacitive touch panel?
A capacitive touch screen is constructed out of glass with a coating of capacitive material
electrodeposited over its surface. Oscillator circuits at the corners of the capacitive glass measure
the capacitance of a person touching the glass surface. Each oscillator will vary in frequency
according to where a person touches the surface. The touch screen controller measures the
frequency changes to determine the X and Y coordinates of the touch. The drawback is that
capacitive touch screen cannot be activated by any non-conductive material, including a gloved
These are three main types:
Surface Capacitive – An exposed ITO conductor on the surface that is touched directly.
Commonly seen in newer household appliances.
Projected Capacitive – Contains two layers of conductors, typically glass. Projected capacitive
has higher accuracy due to the separate scanning of the top and bottom layers. This is the most
common technology used in combination with small format LCD displays.
Single-layer Capacitive – Contains only one layer, with the ITO conductive film underneath
this layer, which is typically glass. Single-layer capacitive has a lower accuracy as the single
conductive layer both emits and receives the signal.
How do you select a touch screen technology?
The four most common touch screen technologies are: resistive, infrared, capacitive, and SAW
(surface acoustic wave). Resistive and capacitive touch screen technologies are the most popular
for industrial and small format applications. If the application requires that operators wear gloves
when using the touch screen, then resistive is preferred over capacitive. Generally, capacitive
technology offers better optical and touch performance, including multiple touch, but is more
expensive than its resistive counterpart.
How does LCD display technology produce color displays?
An LCD is nothing more than a light valve that either allows light to go through the display or
blocks the light from passing. To create a full-color display, each pixel is actually divided into
three rectangular sub-pixels. When combined, these three sub-pixels are dimensionally similar
to a typical square pixel. These sub-pixels are then aligned perfectly with an RGB color filter
that is printed into the LCD cell itself. The color filter is a repeating pattern of Red-Green-Blue
columns, with each color the width of a single rectangular sub-pixel. The result is a display with
3x the original resolution. To obtain a wide range of color combinations, the gray shades of each sub pixels are used in combination to achieve the thousands of unique colors.
Most LCD controllers can be interfaced by what?
common drivers and segment drivers are the two unique types of driver ICs. common drivers
produce signals to create rows or numbers of lines. Segment drivers produce signals to create the
characters or columns.
The controller IC receives data written in ASCII or JIS code from the MPU. This data in stored
in RAM and is then converted into serial character patterns and transferred to the LCD driver IC.
The most commonly used in monochrome graphic and newer TFT LCD modules, the driver/controller IC receives data from the MPU and stores it in RAM. This IC also accepts commands directly from the MPU for both the common and segment drivers.
What are most common types LCD display fluids?
Twisted Nematic (TN) was one of the earliest fluid types to be implemented in LCD displays. Twisted Nematic LCD fluid uses a 90-degree twist between the top and bottom alignment layers of the LCD cell. The contrast of TN fluid displays is very high, but the limitations are that TN fluid can only support a limited multiplex rate, or limited number of rows. These displays are ideal for low information content, like simple character, segmented, or icon-based displays, commonly found in calculators, digital wristwatches, digital clocks, simple meters systems, or any other low information content display application.
Additionally, the TN fluid type is now widely used in full-color TFT displays for its high switching speed, high contrast, and wide viewing angle capabilities. The advent of the active matrix TFT backplane, which employs a transistor at each pixel location, allows a low multiplex rate at each individual pixel location to support the low mux rate requirement of the TN fluid.
Super Twisted Nematic, or STN, is ideal for dot matrix formatted displays, both character and graphic displays, with higher information content. STN is used over TN when the mux rate, or number of rows, is above 8-12. Super Twisted Nematic displays enable this higher mux by increasing the rotation of the molecules from 90 degrees (TN twist) to 260 degrees. This type of crystalline structure is used on almost all passive character and graphic displays of two lines or greater.
Film Compensated Super Twisted Nematic (FSTN) is the same STN fluid technology, but employs an additional compensation layer, retarder, which helps compensate for the STN polarizer’s inability to block or pass some of the circular polarized light that comes through the cell. FSTN is an STN cell with an improved polarizer, which improves the contrast by making a darker pixel with a lighter, more neutral-colored background. In simplest terms it gives a more paper-like, black-on-white appearance.
Types of LCD technology for displaying letters, numbers, & graphics?
Segment LCD: In the most common format, the display segments are arranged to form a figure 8 to display numbers and letters. The same technology can be implemented to construct custom icons of any shape or pattern in an LCD display, as well.
Character Display: The individual pixel units are arranged in 5×7 or 5×8 clusters to form characters. These displays are then characterized by how many rows and columns of pixel clusters, or characters, they can support. For example a 2×16 character display would refer to 2 rows of pixel clusters, or characters, by 16 characters across.
Graphic Display: The LCD display pixels are arranged in rows and columns, which enables the display to depict any text or graphics within the finite number of rows and columns of pixels.
What are the different types of backlights?
EL (Electroluminescent Lamp)
An EL backlight is a solid-state component, which uses colored phosphors to generate light.
These EL backlights are thin, lightweight, and provide very uniform lighting. EL panels are
available in a wide variety of colors. While their power consumption is moderately low, they
require voltages of 100 VAC @ 400 Hz supplied by an inverter that converts a 5, 12, or 24 VDC
input to the AC output. EL backlights also have a limited half-life of 3,000 to 5,000 hours. The
biggest drawbacks to an EL panel are the added cost for the inverter and the limited lifespan. EL
panels are rarely used in new designs today because of these factors
Edge-Lit LED Backlight
Edge-lit LED backlights consist of LEDs placed along the side or sides of a thin plastic light
guide, which then transmit the light evenly through the LCD panel. This is the most common
type of backlighting used today.
Lifetime: 50,000-100,000 hours
Power: 5V DC typical
LED array backlights are composed of surface-mount LEDs, which are configured in a matrix
along the bottom of a shallow plastic tray and encapsulated with a clear epoxy. These LEDs form
a grid across the entire viewing area of the LCD display and emit directly up through a diffuser
film and into the LCD display, rather than from the side like the edge-lit type.
CCFL (Cold Cathode Fluorescent Lamp)
Made of lead glass with mercury, Cold Cathode Fluorescent Lamps are small high-voltage field
emission lamps that provide a fluorescent light source. The CCFLs are used in conjunction with
the plastic light guide to evenly disperse light through the front surface of the LCD panel. Given
the power consumption, the cost, and the hazardous materials, CCFLs are rarely used in today’s
Lifetime: 15,000-30,000 hours
Power: 300V AC typical
What is a backlight?
Backlights are the light-emissive components positioned behind the LCD cell. Backlights are a
part of all transmissive or transflective displays. When an LCD display is used in an environment
where the ambient lighting will not support good reflective-mode visibility, the backlight
luminance is required to give the display contrast and be legible. Backlights are also required
in almost all full-color TFT displays due to the inherently low efficiency of the transmissive
structure of the TFT cell.
What is a NIT?
A NIT is a measurement of light in candelas per meter squared (Cd/m2). The unit is based on the
candela, the SI unit of luminous intensity, and represents a measure of light emitted per unit area.
This is a common metric used in characterizing the brightness of a display device. This can apply
to either the LCD display module as a whole assembly, or a measurement of the backlighting
system alone without the LCD glass.
What is a pixel?
A pixel (a word invented from “picture element”) is the most basic unit of programmable visual content within an LCD display. For a common graphic 128×64 LCD, the display comprises 128 solid columns and 64 solid rows. The display is capable of producing a square pixel in each location where the rows and columns intersect. In this example of a 128×64 display, the LCD display is capable of producing 8,192 unique pixels to be used for simple text and/or graphic images.
What is a resistive touch panel?
A resistive touch panel typically uses a conductive glass backplane with a plastic conductive-
coated inner surface. These conductive inner layers are separated by spacer dots evenly
distributed across the active area. Finger or stylus pressure causes internal electrical contact
at the point of touch, which supplies the touch screen controller with a vertical and horizontal
analog voltage for digitization. The three most common formats are:
Digital – Has a discrete number of touch locations determined by a series of rows and columns
of conductors within the touch panel.
4-wire – Is an analog device that, when combined with the touch screen controller, can identify
any point within the active area of the touch panel.
5-wire – Similar to the 4-wire, but has increased reliability for more extensive use-based
What is a Sunlight Readable or Outdoor Readable LCD?
Born of a need for outdoor applications and a lack of available transflective panels, Sunlight
Readable Displays combine the right type of anti-reflective front polarizer and high-efficiency
rear polarizer, allowing the cell to reuse some of the sunlight’s energy. Used in concert with
a higher-brightness backlight, the overall image quality in an indoor, high ambient light
environment is greatly improved. It is important to note that in order for the Sunlight Readable
Display to function properly in an outdoor environment, the backlight will need to be engaged.
The Sunlight Readable TFT Display is capable of reflecting more light, making it better suited
for use in direct, outdoor sunlight than a standard transmissive display. In this configuration
the display is considered to be Sunlight Readable, but it will not be as efficient in reflective
mode as the true transflective TFT cell. To further enhance the user experience in direct sunlight
conditions, it is also recommended that the user limit the image content to high-contrast images
What is a Surface Acoustic Wave (SAW) touch screen?
A SAW touch screen uses a solid glass display as the touch sensor. Across the surface of the
glass, two surface acoustic sound waves are transmitted – one for vertical detection and the other
for horizontal detection. Each sound wave spreads across the screen by bouncing off reflector
arrays along the edges of the display, and is detected by two receivers for each axis. The time
at which the sound waves arrive at each receiver is known because the velocity of the acoustic
wave through the glass is known and the size of the display is fixed. When the user touches the
glass surface of the display, some of the energy of the acoustic wave is absorbed by the water
content of the user’s finger. The controller measures the time at which the received amplitude
dips to determine the X and Y coordinates of the touch location. In addition to the X and Y
coordinates, SAW technology can also provide Z axis (depth) information. The harder the user
presses, the more energy the finger will absorb.
What is a viewing angle?
This is the angle representing the preferred viewing direction where the LCD display exhibits the
highest contrast. Viewing angles are usually defined in the horizontal and vertical directions, and
measured in degrees perpendicular to the LCD surface. As the user physically moves to either
side of the LCD screen, the images displayed will degrade.
The preferred viewing direction or viewing angle is defined with respect to the hands of a clock.
The most common angles are typically either 6 O’clock (viewed from below) or 12 O’clock
(viewed from above).
What is an infrared touch screen?
An infrared touch screen surrounds the face of the display with a bezel of light-emitting diodes
(LEDs) and diametrically opposing phototransistor detectors. A sequence of pulses is directed
to each of these LEDs by the controller circuitry directs, which scan the screen with invisible
infrared light beams just in front of the surface. The controller then detects the location where the
light beams become obstructed by any object.
What is an LED (Light Emitting Diode)?
An LED (Light Emitting Diode) is the most commonly used component in backlights. LEDs are
solid-state semiconductor devices that convert electrical energy directly into visible light. Two
semiconductor materials are joined such that when a current is passed through the LED, light and
heat are generated at the junction.
What is Chip-On-Board (COB)?
Chip-On-Board is the construction method with the LCD driver wafer mounted on the PCB with
contacts facing up. The contacts are then wire bonded to the PCB pads, followed by a complete
epoxy encapsulation for a hermetic seal.
What is Chip-On-Flex (COF)?
Chip-On-Flex is where the LCD driver is mounted directly to a flexible circuited board. These
IC-Flex combinations would come from the driver manufacturer on a reel form referred to as
TAB, or tape automated bonding. In the past, this was a very useful configuration of LCD driver
ICs, as they take up much less space on the LCD glass ledge. However, they are much less
common today due to the additional cost of the film.
What is Chip-On-Glass (COG)?
Chip-On-Glass is the mounting of the LCD IC directly onto the ledge of the LCD glass itself.
The IC is bonded with an anisotropic conductive film (ACF), which facilitates the mechanical
adhesion, as well as the conduction from the IC to the glass.
What is dot pitch or pixel pitch?
The dot pitch or pixel pitch is defined as the distance between the edge of a pixel and the same
edge of the neighboring pixel. The dot pitch is measured in millimeters (mm), with a smaller
number typically translating into a sharper image. Concurrently, a smaller pixel pitch for the
same resolution LCD display will also result in a smaller image.
What is the brightness requried for each application?
Each color display application will vary depending on the intended use of the LCD, the contrast,
and the ambient light environment that the display is in. A typical standard notebook or desktop
LCD display in office lighting conditions are in the 200-250 NIT range. In an LCD display
intended for mixed use of both indoors and with the potential for uncontrolled or indirect
sunlight, 500-900 NITs is recommended. For mainly outdoor or direct sunlight applications,
1,000 NITs or above is suggested.
If the color display has transflective properties, then the backlight does not need to compete with
the ambient sunlight. In this outdoor application, the glass will revert to a reflective mode, and
the display only needs to rely on the backlight for the indoor or low-light applications.
Monochrome displays do not have the same requirements. As most monochrome displays can
easily adopt a rear transflective polarizer, there is no need to have a bright backlight compete
with the sun in an outdoor application. The transflective properties will suffice, and therefore the
backlight only needs to support the indoor or low-light applications. Additionally, the content
of a monochromatic black-on-white image does not require the same brightness as a full-color
TFT display to maintain good viewability of the content. A typical monochrome LCD will be
anywhere between 15 to 150 NITs.
What is the contrast ratio?
The contrast ratio is the ratio of the luminance between a pixel in the “light” state compared to
the same pixel in the “dark” sate. Typical contrast ratios for the different technologies are:
• TN 9:1
• STN 10:1
• FSTN 15:1
• CSTN 25:1
• TFT 300:1 and up
What is the definition of a duty rate?
A duty rate, also known as the multiplex rate, is the fraction of the total frame time that each row
of the LCD is addressed.
What is the definition of bias ratio?
The bias ratio of an LCD, or the voltage margin, is defined as the ratio of V on (voltage on pixels
that are currently addressed to the ON-state) divided by V off (voltage on pixels that are not
Active-matrix VS. passive-matrix LCD displays?
Passive-matrix LCD is an LCD technology that uses a grid of vertical and horizontal conductors
comprised of Indium Tin Oxide (ITO) to create an image. Each pixel is controlled by an
intersection of two conductors. By creating a potential voltage difference at an intersection, the
LC fluid is able to respond by creating an “on” state at that intersection, also commonly referred
to as a pixel.
While relatively simple and inexpensive to produce, passive-matrix displays do have a few
drawbacks. Because the charge of the two conductors (rows and columns) is addressed only one
row at a time, the response time of passive-matrix displays is relatively slow, and the contrast is
greatly reduced over that of an active TFT display.
An active-matrix display, or Thin Film Transistor (TFT), utilizes a silicon backplane instead of
the more basic Indium Tin Oxide (ITO) conductive surface used on the passive LCD display.
This silicon backplane enables the creation of a transistor at each pixel location, which holds the
LCD charge in between row-addressing cycles. This main charge-holding difference allows the
active-matrix LCD to use a TN LC fluid with active addressing, which results in higher contrast,
reduced response time, and better viewing angles. Active-matrix displays are usually combined
with a color filter to create a full-color TFT cell.
What is the difference between anti-glare and anti-reflection?
Glare and reflection are terms that are often confused. Both anti-glare and anti-reflective
enhancements attempt to improve or optimize readability while using different techniques to
address the causes of reduced readability due to external ambient light sources.
Anti-glare deals with external sources of reflection off a surface – like bright sunlight or high
ambient lighting conditions – by using diffusion to disperse the reflected light from the surface.
Diffusion works by reducing the coherence of the image that is reflected on the screen, making
this unwanted image unfocused to the user’s eye, and thereby mitigating its interference with
the viewing of the intended image. This comes at the sacrifice of clarity and resolution of the
intended image. While economical to apply, the trade-off in image clarity caused makes anti-
glare an inferior solution to anti-reflection.
Unlike the diffusion-based anti-glare solutions, anti-reflection takes into account both internal
and external sources of accumulated reflection. As light passes from one medium to another,
the difference between the index of refraction in the adjacent surfaces creates transitional phase
difference, which increases the amount of light reflected. These reflections are cumulative and
cause the display to become “washed out,” which reduces the contrast and the overall readability
of the LCD display. The anti-reflective coatings consist of transparent, thin film structures with
alternating layers of contrasting refractive index, which results in destructive interference in the
light reflected from the interfaces, and constructive interference in the corresponding transmitted
A typical amorphous silicon TFT LCD exhibits a contrast of approximately 300 to 700 in a dark
room transmissive mode measurement. The contrast on the same unit measured under ambient
illumination is drastically lowered due to surface reflection or glare. A standard 200 NIT LCD
display measured in a dark room may have a 300:1 contrast ratio, but could then measure less
than 2:1 in direct sunlight. This is due to the fact that the surface glare increases the luminance
by over 200 NITs, both on the “white” and the “black” that are produced on the display screen.
Resulting luminance of the white is slightly over 400 NITs and the luminance of the black is
slightly over 200 NITs, causing the contrast ratio to then drop to less than 2:1 and the picture
quality to become drastically reduced.
What is viewing cone?
The viewing cone is the maximum viewing angle range that the display can either support a
minimum contrast value, or not become inverted. For example, a monochrome display might
support a contrast ratio of 2:1 minimum when viewed at 45 degrees from perpendicular in every
direction around the display. Beyond 45 degrees, the contrast will dip below 2:1. Often these
cones are not perfectly symmetrical.
What types of interfaces are available LCD Controller?
Most LCD controllers can be interfaced by an 8-bit, 4-bit, or 2-bit I2C, or 1-bit interface.
Can I Put a Touch Panel on Any Display?
Product life cycle & How to handle obsolescence
Most of our displays run 7-10 years. And as long as our customers are still buying the configuration, we would not obsolete the LCD display. In the case where the LCD IC driver or the color TFT glass used in the display becomes obsolete, we create a design around the closest replacement, identify any differences, and work with our customers on a last time buy strategy to manage any gap in supply while developing the replacement display.
How do I know what kind of display I need?
Call us. We always start with your end product and study what you are trying to accomplish with the display content, who your customer is and how they will be using the device. From that information, we can determine the right display technology and then we work with your product to integrate in the most effective and cost efficient manner possible.
What are the different interconnect options available?
The most common is a flex to ZIFF style connection. The other available options are board-to-board connectors, pins for thru-hole soldering, Elastomeric or Zebra connectors, and in some rare instances a customer may elect to use a Hot-Bar solder process directly to a PCB.
Sample & production lead-time for a display. Is expediting possible?
Standard Product sample lead-time ranges from 3 days to 2 weeks
Custom displays aretypically 5-8 weeks
Production lead-time is 8 weeks and then 4 weeks for traditional ocean shipping to the AZ warehouse
We can expedite whenever requested, and it is case by case depending on what is possible.
What is the minimum order quantity for a program?
It depends on the display type. For the larger more complicated display we can do as little as 1K/ yr and the more common typical display is closer to 5K/ yr. We can spread out this quantity over the 12 month period.
Can you ship anywhere? Shipping terms & will you stock?
Yes, for non US domestic shipping locations we can ship ExWorks Hong Kong. And for customers manufacturing in the US, we warehouse in Arizona and ship from the Arizona warehouse. We will stock product in either China or Arizona.
Where do you manufacture displays?
We have three manufacturing locations, the exact facility depends on the product technology. Southern China (Shenzhen) Central China (Shanghai) and Northern China (Beijing)
Can you match the display that I am getting from my supplier?
Yes, in almost all cases. For monochrome displays we would re-tool the LCD glass, backlight, PCB and anything else that is applicable for the display. And as long as the LCD driver IC is still available in production we guarantee a 100% identical replacement. In the case that the IC is no longer available, we will recommend a replacement IC which is often 100% compatible or in some cases requires a minor software update.
For color TFT projects, we would use a common TFT glass platform and tool up the balance of the components to match the original design. And the same holds true, as long as the TFT glass is still available in production we guarantee a 100% identical replacement. In the case that the TFT LCD is no longer available, we will recommend a replacement, which is often 100% compatible as well.
Please see Phoenix Display’s cross-match program:
Tooling difference of a custom monochrome display VS a color TFT?
We manufacture the monochrome LCD glass in house. The tooling portion of the mono glass is about $2500-$3500. Because of the high expense of color TFT tooling and the high MOQ’s, we typically design around a standard TFT glass size and resolution. If a custom color TFT display solution is required the tooling can range from $125,000-$350,000 and the MOQ would be 10K-100K depending on the design.
What are the tooling costs?
There is a wide range depending on the product, we can change the glass type for no tooling, and simple PCB changes are around $1000 or less. The full custom monochrome display will be around $4000-$6000. Designing a semi-customer display around a standard TFT glass platform is $1000-$5000. And tooling up a full custom TFT glass platform can be anywhere from $125,000-$350,000, which is why most of our color TFT customers choose to go semi-custom and use an existing standard glass cell.
Can I modify an existing standard display?
Yes, we consider this semi-custom, and anything is possible. The benefits are lower tooling and the potential to use the standard display for testing while the tooling for the customization is in process.
When should I choose to go custom?
There are two different scenarios:
For a new design: It’s typically either a volume based issue, where the volume is high enough ( 5-10K/yr) to justify the piece price savings, or if there are mechanical constraints that dictate the design be custom.
For our cross matching program we usually do a custom display so there is no impact to our end customer’s product when crossing over with a Phoenix Display module.
Are custom displays more expensive than standard displays?
No, a custom display only implies that there is some element of tooling involved. Custom displays are generally less expensive as they are designed specifically for the application.