minimum clock speed needed for lcd tft display brands

Since the display includes the Ilitek ILI9320 controller, then your interface requirements are much lower, as the microcontroller no longer has to interface directly with the TFT and instead only talks to the controller chip via a simple interface: either SPI, which takes six wires: RS, CS, CLK, MOSI, MISO and RESET. Or you can use an 8080-compatible parallel interface which takes 13 wires: an 8-bit data bus, and RS, CS, WR, RD and RESET. (There are options to use larger data-buses, up to 18 bits, but I don"t recommend that for a low end microcontroller.)

There are two optional interfaces in which the microcontroller generates all of the clock signals (VSYNC, HSYNC and DOTCLK); you don"t want to do that since it would require a high-end controller.

So just about any microcontroller will do, however you need to have enough flash memory to hold whatever static items you want to display; for example if you are going to be displaying text then you will need to allocate arrays to store bitmaps for whatever fonts you will use. Even a small font can take 60KB.

This note will discuss the considerations made when choosing a microcontroller that will work for your display. A few requirements need to be met depending on the display’s features, interface, and size. These can also be determined by the embedded IC in the display. An overview of the considerations when choosing a microcontroller can be seen below. It should be noted that these items are separated for definition but may serve the same purpose and be interconnected in the ecosystem of the controller.

Application and display specific peripheral requirements. I2C, SPI, UART, Parallel, MIPI, LVDS, HDMI etc. Determines pin connections and required architecture of the device.

Flash and RAM memory requirements. Minimum frame buffer memory is dependent on the size andresolution of the display. Location of memory (external or internal) can restrict interface speed and must becompatible with the chosen interface.

Communication speed requirements defined by the interface and intended application. Refresh rateis determined on the size of the display and location of memory. This will indicate which processors arecompatible.

A displays embedded IC can offer resources such as internal RAM, clock generators and power control.This can save resources otherwise needed to be provided externally. Check the datasheet of the display’s ICcontroller for device function specifics.

Availability of resources for programming and debugging the microcontroller. Online resources andexampleprograms to leverage from can a lot of save time. Compatibility with a familiarprogramming environment isadditionally beneficial.

The interface selection is dependent on the intended application of the display. Each display has a different interface or different choices for a connection interface. For smaller displays a 3/4-wire serial interface would be sufficient. For larger display’s with high resolution a faster interface should be chosen. A parallel RGB interface is capable of high-speed data transmission however requires many pin connections. If the intended application for the display is video a MIPI, LVDS or HDMI connection would be a good choice.

The available memory of a microcontroller often becomes a highlighted issue when determining which microcontroller to select. The microcontroller needs a minimum amount of RAM to hold the frame buffer of the display. Even small displays require more RAM than a typical microcontroller possess. To verify that your microcontroller will have enough memory, it is important to calculate the frame buffer.

The minimum RAM required for the frame buffer in this example would then be 768kB. It is important to note that external RAM can be provided for the frame buffer if the microcontroller does not provide it internally. Clocking speed should be verified if using external RAM as the microcontroller cannot access external RAM as quickly. The clock frequency constrained by external RAM sometimes does not meet the minimum requirements of some very high-speed interfaces (ex. DSI-MIPI). Additionally, the display can contain some form of RAM depending on the IC controller inside the display. This can be verified on the specification sheet of the IC.

The speed of the microcontroller is heavily dependent on the interface used in the application. The minimum and maximum of the clock frequency is specified in the datasheet of the display and in the specification sheet of the display’s controller IC. The frame rate is typically around 50-60Hz, which is the median oscillation frequency to refresh the display to maintain an image. The display will often provide an internal high frequency clock that can be initialized to certain frequencies.

It is important to verify in the controller data sheet which resources are provided by the internal IC of the display. Some key information to look for would be: Does the display have sufficient RAM or does this need to be provided? Does the display have an internal oscillator for clock generation for the interface chosen? An additional graphics controller can be used to interface the display with the microcontroller to meet these requirements. Features like these can be utilized to avoid additional cost, space, and memory of your application.

After a brief consideration of intended application and interface of the display you can get some idea of which microcontroller processor and architecture you will need. There are a few different microcontroller processors to choose from. The main choices are ARM, AVR, PIC, and 8051. The difference between them is the bit size of the processor, 8-bit, 16-bit, 32-bit or 64-bit data . The data bit width is the amount of data that can be sent at a time. This determines the speed of data transfer and thus compatible applications and interfaces.

The AVR has an 8-bit processor and is a RISC type microcontroller. This type of processor is compatible with low speed interfaces (SPI, I2C) and smaller displays. A common AVR microcontroller board is the Arduino which has the embedded 8-bit ATMEL RISC processors. These processors are widely popular which provide the benefit of numerous online resources and availability. The Arduino processors (ATmega/SAM3X) are typically available in most microcontroller programming environments. Additionally, Arduino offers 32-bit AVR development boards which function closely to the ARM processors.

The AVR microcontrollers are constrained by the low frequency, internal memory availability and power costs. AVR’s cannot use external program memory but some may allow expansion of external SRAM. These microcontrollers alone would be incompatible for high frequency applications such as video, large displays, or capacitive touch panels.

The ARM microprocessors have a RISC architecture. They offer 32-bit or 64-bit processors and are great options for high speed interfaces (Parallel, LVDS, MIPI, HDMI) and high-resolution displays. Common ARM processors can be found from STMicroelectronics and Raspberry Pi. The most common version of the ARM processors is the “Microcontroller” Arm-M group which include the Cortex-M0 and Cortex-M4 series.

The ARM processors are compatible with most displays and connection interfaces. These microcontrollers have become increasingly popular, so the cost has become comparable between the ARM and the AVR types. These processors provide the speed, but it is recommended to verify the available RAM as these boards vary widely on included features.

The PIC architecture consists of 8, 16, and 32-bit processors developed by Microchip. The PIC 32-bit series of microcontrollers have been geared toward graphical embedded applications and there are a lot of resources online for these devices. There is a huge variety of PIC controllers which make them easily available. These microcontrollers are known for being low cost and are comparable to the ARM processors. The drawback of the PIC controllers is using Microchips programming environment, but this is based on preference.

The Intel MCS-51, more commonly known as the 8051 microcontrollers have a CISC architecture and an 8-bit processor. These processors differ in architecture from the previous and are programmed using a combination of C and assembly languages. The program memory is read only and does not have an on-board ISP. A special programming device is needed to rewrite the EEPROM or flash memory. These processors are typically small, low cost and low powered. This can make them favorable for battery powered devices. These processors are commonly used to initialize TFT displays and are combined with a graphics controller to provide the required resources such as RAM and clock frequency.

Development environments and online resources become considerably valuable when creating an application for your display. A brand new or uncommon microcontroller will have very few resources for reference. Even knowledgeable engineers can find frustrations with the manufacturers programming environments. There are many microcontroller choices that will support your display with similar and overlapping features. Choosing a microcontroller with an available FAQ, application notes or is accessible on a familiar programming platform can save a lot of time.

Buyers and others who are developing systems that incorporate FocusLCDs products (collectively, “Designers”) understand and agree that Designers remain responsible for using their independent analysis, evaluation and judgment in designing their applications and that Designers have full and exclusive responsibility to assure the safety of Designers" applications and compliance of their applications (and of all FocusLCDs products used in or for Designers’ applications) with all applicable regulations, laws and other applicable requirements.

Designer agrees that prior to using or distributing any applications that include FocusLCDs products, Designer will thoroughly test such applications and the functionality of such FocusLCDs products as used in such applications.

Low voltage differential signaling (LVDS, also known as OpenLDI) thin-film transistor (TFT) liquid crystal (LCD) displays typically have a specified resolution and minimum required clock frequency to meet desired resolution. Normally, you will find this information listed in the display data sheet and won’t need to perform any calculations.

However, if you do not yet have access to your display data sheet and only know what resolution you want your system to support, you can estimate what clock frequency you need and determine which serializer/deserializer (SerDes) is appropriate for your application.

%Blanking: The blanking period, or the percentage of time when active video is not being displayed. As shown in Figure 1, it is represented horizontally as horizontal pulse width (HPW), horizontal back porch (HBP) and horizontal front porch (HFP). It is also represented vertically as vertical pulse width (VPW), vertical back porch (VBP) and vertical front porch (VFP).

The values for these blanking parameters are listed in display data sheets. The total blanking period varies from 3% to 39%. If your system uses reduced blanking, then you can estimate %Blanking at 10%. If you are not sure what blanking period your system uses, estimate around 20% and above to be conservative.

Frame rate (or refresh rate):the frequency at which consecutive images (frames) are displayed, and is measured in hertz or frames per second (fps). 60Hz is the most common frame rate, but this value can vary from 24Hz to 70Hz.

Throughput is another metric that you can use to determine whether or not a device will support your desired display resolution. The throughput is the effective payload of video data, and is derived from the required pixel clock frequency and color depth of your system, as shown in Equation 2:

Color depth: For a first-generation SerDes like the SN65LVDS93A, color depth is typically 24-bit red-green-blue (RGB) or 18-bit RGB for single pixel in, single pixel out (SISO) applications, and 48-bit RGB or 36-bit RGB for dual pixel in, dual pixel out (DIDO) applications.

The color depth will determine how many LVDS data lanes your display requires. SerDes serialize data at a rate of 7x the pixel clock frequency on each LVDS data lane. If the color depth is 24-bit RGB, then you will need four LVDS data lanes (there are an additional four bits used for control, which brings the total bit count to 28 bits) and can use a SerDes like the SN65LVDS93A. If the color depth is 18-bit RGB, then you will need three LVDS data lanes (there are an additional 3 bits used for control, which brings the total bit count to 21 bits) and can use a SerDes like the SN74LVDS84A or the SN65LVDS93A.

If the color depth is 48-bit RGB, then you will need eight LVDS data lanes (there are an additional 8 bits used for control, which brings the total bit count to 56 bits) and will need to use a device like the DS90C387 or DS90C189-Q1, which can output as many as eight LVDS data lanes.

When calculating the throughput for DIDO applications, you need to calculate the throughput for the odd pixels and even pixels separately and then add them together. For example, for a 48-bit DIDO application, the total required throughput would be 2 x Pixel Clock x 24.

Since the color depth is 24-bit RGB, you will need four LVDS data lanes. The SN65LVDS93A is a good fit for this application, since it has a pixel clock frequency range of 10MHz to 135MHz. Additionally, the maximum throughput for each LVDS data lane on this device is 135 x 7 = 945Mbps. Because this device has four LVDS data lanes, the total maximum throughput is 945 x 4 = 3780Mbps, which is higher than the minimum required throughput.

So the minimum pixel clock frequency to support a 2048 x 1536 resolution display is 208MHz. However, since this is a 48-bit DIDO application, there are actually two clocks: the frequency is split between them. Each clock must have a frequency of at least 104MHz.

Since the color depth is 48-bit RGB, you will need eight LVDS data lanes. The DS90C387 and DS90C187 are a good fit for this application, since they have a pixel clock frequency range of 32.5MHz to 112MHz (the DS90C387) and 25MHz to 105MHz (the DS90C187) for each channel in DIDO applications. Thus, if you don’t have access to the display data sheet yet, you can still estimate the required pixel clock frequency and throughput to support your desired resolution. If the SerDes does not meet these parameters, data on the display may display incorrectly, or not display at all.

Let us start with the basics first; refresh the knowledge about TN and LCD displays in general, later we will talk about TFTs (Thin Film Transistors), how they differ from regular monochrome LCD displays. Then we will go on to the ghosting effect, so we will not only discuss the technology behind the construction of the TFT, but also some phenomena, like the ghosting effect, or grayscale inversion, that are important to understand when using an LCD TFT display.

Next, we will look at different technologies of the TFT LCD displays like TN, IPS, VA, and of course about transmissive and transflective LCD displays, because TFT displays also can be transmissive and transflective. In the last part we will talk about backlight.

Let us start with a short review of the most basic liquid crystal cell, which is the TN (twisted nematic) display. On the picture above, we can see that the light can be transmit through the cell or blocked by the liquid crystal cell using voltage. If you want to learn more about monochrome LCD displays and the basics of LCD displays, follow this link.

What is a TFT LCD display and how it is different from a monochrome LCD display? TFT is called an active display. Active, means we have one or more transistors in every cell, in every pixel and in every subpixel. TFT stands for Thin Film Transistor, transistors that are very small and very thin and are built into the pixel, so they are not somewhere outside in a controller, but they are in the pixel itself. For example, in a 55-inch TV set, the TFT display contains millions of transistors in the pixels. We do not see them, because they are very small and hidden, if we zoom in, however, we can see them in every corner of each pixel, like on the picture below.

On the picture above we can see subpixels, that are basic RGB (Red, Green, Blue) colors and a black part, with the transistors and electronic circuits. We just need to know that we have pixels, and subpixels, and each subpixel has transistors. This makes the display active, and thus is called  the TFT display. TFT displays are usually color displays, but there are also monochrome TFT displays, that are active, and have transistors, but have no colors. The colors in the TFT LCD display are typically added by color filters on each subpixel. Usually the filters are RGB, but we also have RGBW (Red, Green, Blue, White) LCD displays with added subpixels without the filter (White) to make the display brighter.

Going a little bit deeper, into the TFT cell, there is a part inside well known to us from the monochrome LCD display Riverdi University lecture. We have a cell, liquid crystal, polarizers, an ITO (Indium Tin Oxide) layer for the electrodes, and additionally an electronic circuit. Usually, the electronic circuit consists of one transistor and some capacitors to sustain the pixel state when we switch the pixel OFF and ON. In a TFT LCD display the pixels are much more complicated because apart from building the liquid crystal part, we also need to build an electronic part.

That is why TFT LCD display technologies are very expensive to manufacture. If you are familiar with electronics, you know that the transistor is a kind of switch, and it allows us to switch the pixel ON and OFF. Because it is built into the pixel itself, it can be done very quickly and be very well controlled. We can control the exact state of every pixel not only the ON and OFF states, but also all the states in between. We can switch the light of the cells ON and OFF in several steps. Usually for TFT LCD displays it will be 8-bit steps per color, so we have 256 steps of brightness for every color, and every subpixel. Because we have three subpixels, we have a 24-bit color range, that means over 16 million combinations, we can, at least theoretically, show on our TFT LCD display over 16 million distinct colors using RGB pixels.

Now that we know how the TFT LCD display works, we can now learn some practical things one of which is LCD TFT ghosting. We know how the image is created, but what happens when we have the image on the screen for a prolonged time, and how to prevent it. In LCD displays we have something called LCD ghosting. We do not see it very often, but in some displays this phenomenon still exists.

If some elements of the picture i.e., your company logo is in the same place of the screen for a long period of time, for couple of weeks, months or a year, the crystals will memorize the state and later, when we change the image, we may see some ghosting of those elements. It really depends on many conditions like temperature and even the screen image that we display on the screen for longer periods of time. When you build your application, you can use some techniques to avoid it, like very rapid contrast change and of course to avoid the positioning the same image in the same position for a longer time.

You may have seen this phenomenon already as it is common in every display technology, and even companies like Apple put information on their websites, that users may encounter this phenomenon and how to fix it. It is called image ghosting or image persistence, and even Retina displays are not free of it.

Another issue present in TFT displays, especially TN LCD displays, is grayscale inversion. This is a phenomenon that changes the colors of the screen according to the viewing angle, and it is only one-sided. When buying a TFT LCD display, first we need to check what kind of technology it is. If it is an IPS display, like the Riverdi IPS display line, then we do not need to worry about the grayscale inversion because all the viewing angles will be the same and all of them will be very high, like 80, 85, or 89 degrees. But if you buy a more common or older display technology type, like the TN (twisted nematic) display, you need to think where it will be used, because one viewing angle will be out. It may be sometimes confusing, and you need to be careful as most factories define viewing direction of the screen and mistake this with the greyscale inversion side.

On the picture above, you can see further explanation of the grayscale inversion from Wikipedia. It says that some early panels and also nowadays TN displays, have grayscale inversion not necessary up-down, but it can be any angle, you need to check in the datasheet. The reason technologies like IPS (In-Plane Switching), used in the latest Riverdi displays, or VA, were developed, was to avoid this phenomenon. Also, we do not want to brag, but the Wikipedia definition references our website.

We know already that TN (twisted nematic) displays, suffer from grayscale inversion, which means the display has one viewing side, where the image color suddenly changes. It is tricky, and you need to be careful. On the picture above there is a part of the LCD TFT specification of a TN (twisted nematic) display, that has grayscale inversion, and if we go to this table, we can see the viewing angles. They are defined at 70, 70, 60 and 70 degrees, that is the maximum viewing angle, at which the user can see the image. Normally we may think that 70 degrees is better, so we will choose left and right side to be 70 degrees, and then up and down, and if we do not know the grayscale inversion phenomena, we may put our user on the bottom side which is also 70 degrees. The viewing direction will be then like a 6 o’clock direction, so we call it a 6 o’clock display. But you need to be careful! Looking at the specification, we can see that this display was defined as a 12 o’clock display, so it is best for it to be seen from a 12 o’clock direction. But we can find that the 12 o’clock has a lower viewing angle – 60 degrees. What does it mean? It means that on this side there will be no grayscale inversion. If we go to 40, 50, 60 degrees and even a little bit more, probably we will still see the image properly. Maybe with lower contrast, but the colors will not change. If we go from the bottom, from a 6 o’clock direction where we have the grayscale inversion, after 70 degrees or lower we will see a sudden color change, and of course this is something we want to avoid.

To summarize, when you buy older technology like TN and displays, which are still very popular, and Riverdi is selling them as well, you need to be careful where you put your display. If it is a handheld device, you will see the display from the bottom, but if you put it on a wall, you will see the display from the top, so you need to define it during the design phase, because later it is usually impossible or expensive to change the direction.

We will talk now about the other TFT technologies, that allow us to have wider viewing angles and more vivid colors. The most basic technology for monochrome and TFT LCD displays is twisted nematic (TN). As we already know, this kind of displays have a problem with grayscale inversion. On one side we have a higher retardation and will not get a clear image. That is why we have other technologies like VA (Vertical Alignment), where the liquid crystal is differently organized, and another variation of the TFT technology – IPS which is In-Plane Switching. The VA and IPS LCD displays do not have a problem with the viewing angles, you can see a clear image from all sides.

Nowadays all TV sets, tablets and of course mobile phones are IPS or VA. You can turn them around and see the image clear from all sides. But, for monitor applications the TN technology is still widely used, because the monitor usually is in front of you and most of the time you look directly at it, from top, left or right side, but very rarely from the bottom, so the grayscale inversion viewing angle can be placed there. This technology still is very practical because it is affordable and has some advantages for gamers because it is very fast.

Apart from the different organization of the liquid crystals, we also organize subpixels a little bit differently in a VA and IPS LCD displays. When we look closer at the TN display, we will just see the subpixels with color filters. If we look at the VA or IPS display they will have subpixels of subpixels. The subpixels are divided into smaller parts. In this way we can achieve even wider viewing angles and better colors for the user, but of course, it is more complicated and more expensive to do.

The picture above presents the TN display and grayscale inversion. For IPS or VA technology there is no such effect. The picture will be the same from all the sides we look so these technologies are popular where we need wide viewing angles, and TN is popular where we don’t need that, like in monitors. Other advantages of IPS LCD displays are they give accurate colors, and wide viewing angles. What is also important in practice, in our projects, is that the IPS LCD displays are less susceptible to mechanical force. When we apply mechanical force to the screen, and have an optically bonded touch screen, we push the display as well as squeeze the cells. When we have a TN display, every push on the cell changes the image suddenly, with the IPS LCD displays with in-plane switching, different liquid crystals organization, this effect is lesser. It is not completely removed but it is much less distinct. That is another reason IPS displays are very popular for smartphones, tablets, when we have the touchscreens usually optically bonded.

If we wanted to talk about disadvantages, there is a question mark over it, as some of them may be true, some of them do not rely on real cases, what kind of display, what kind of technology is it. Sometimes the IPS displays can have higher power consumption than others, in many cases however, not. They can be more expensive, but not necessarily. The new IPS panels can cost like TN panels, but IPS panels definitely have a longer response time. Again, it is not a rule, you can make IPS panels that are very fast, faster than TN panels, but if you want the fastest possible display, probably the TN panel will be the fastest. That is why the TN technology is still popular on the gaming market. Of course, you can find a lot of discussions on the internet, which technology is better, but it really depends on what you want to achieve.

Now, let us look at the backlight types. As we see here, on the picture above, we have four distinct types of backlight possible. The most common, 95 or 99 per cent of the TFT LCD displays on the market are the transmissive LCD display type, where we need the backlight from the back. If you remember from our Monochrome LCD Displays lecture, for transmissive LCD displays you need the backlight to be always on. If you switch the backlight off, you will not see anything. The same as for monochrome LCD displays, but less popular for TFT displays, we have the transflective LCD display type. They are not popular because usually for transflective TFT displays, the colors lack in brightness, and the displays are not very practical to use. You can see the screen, but the application is limited. Some transflective LCD displays are used by military, in applications where power consumption is paramount; where you can switch the backlight off and you agree to have lower image quality but still see the image. Power consumption and saving energy is most important in some kind of applications and you can use transflective LCD displays there. The reflective type of LCD displays are almost never used in TFT. There is one technology called Low Power Reflective Displays (LPRD) that is used in TFT but it is not popular. Lastly, we have a variation of reflective displays with frontlight, where we add frontlight to the reflective display and have the image even without external light.

Just a few words about Low Power Reflective Displays (LPRD). This kind of display uses environmental light, ambient light to reflect, and produce some colors. The colors are not perfect, not perfectly clear, but this technology is becoming increasingly popular because it allows to have color displays in battery powered applications. For example, a smartwatch would be a case for that technology, or an electrical bike or scooter, where we can not only have a standard monochrome LCD display but also a TFT LCD color display without the backlight; we can see the image even in

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strong sunlight and not need backlight at all. So, this kind of TFL LCD display technology is getting more and more popular when we have outdoor LCD displays and need a low power consumption.

On the picture above, we have some examples of how transmissive and reflective LCD displays work in the sunlight. If we have a simple image, like a black and white pattern, then on a transmissive LCD display, even with 1000 candela brightness, the image probably will be lower quality than for a reflective LCD display; if we have sunlight, we have very strong light reflections on the surface of the screen. We have talked about contrast in more detail in the lecture Sunlight Readable Displays. So, reflective LCD displays are a better solution for outdoor applications than transmissive LCD displays, where you need a really strong backlight, 1000 candela or more, to be really seen outdoors.

To show you how the backlight of LCD displays is built, we took the picture above. You can see the edge backlight there, where we have LEDs here on the small PCB on the edge, and we have a diffuser that distributes the light to the whole surface of LCD screen.

In addition to the backlight, we have something that is called a frontlight. It is similar to backlight, it also uses the LEDs to put the light into it, but the frontlight needs to be transparent as we have the display behind. On the example on the picture above we can see an e-paper display. The e-paper display is also a TFT display variation, but it is not LCD (liquid crystal), it is a different technology, but the back of the display is the same and it is reflective. The example you see is the Kindle 4 eBook reader. It uses an e-paper display and a frontlight as well, so you can read eBooks even during the night.

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In this Display 101 article we discuss thedigital parallelRGB LCD display interface and how the row and column driving signals are generated from the digital parallel RGB interface.

An LCD display consists of an array of liquid crystal segments. The crystal itself doesn’t emit light. With no electrical field, crystals organize in a random pattern. When an electric field is applied, the crystals align to the electrical field. Various strength of electric fields works like a “gate” to pass different intensity of backlight through the crystals. If the crystals are aligned perpendicular to the backlight, then the backlight can’t pass through the crystals. [1]

From the electronic structure point of view, an LCD panel consists of a grid of electrical signals. The pixels are addressed by a matrix where every interaction belongs to a pixel. Each pixel is connected perpendicularly to the row and column through a transistor. When the row and column are selected by an IC controller, the responding pixel at the interaction of the row and the column is enabled or disabled.[2]

How to generate a specific color for a pixel? Each pixel is composed of 3 segments that individually pass light through a red, green, and blue filter, to make an RGB display color pixel. For a 320*240 RGB TFT display, there are 960 (320*3) columns and 240 rows.

Most LCD displays have a digital parallel RGB interface. It works between the graphic controller as a signal source and the input of the RGB display module.

The image data is transmitted digitally as “0 ”or “1 “ by TTL voltage levels. For the RGB interface, each of the signals has a corresponding line. Below are the signal connections of the LCD RGB display interface of 24 bits per pixel.

The same principle is applied to the HSYNC syncpulse, marked with HBP and HFP. The HSYNC pulse is responsible for a new row.Between twoHSyncpulses, the grey level RGB color data for one row (line) needs to be transmitted.[4]

In the past decade, LCD monitors have replaced CRT screens for all but the most specialist applications. Although liquid crystal displays boast perfect

In market, LCD means passive matrix LCDs which increase TN (Twisted Nematic), STN (Super Twisted Nematic), or FSTN (Film Compensated STN) LCD Displays. It is a kind of earliest and lowest cost display technology.

LCD screens are still found in the market of low cost watches, calculators, clocks, utility meters etc. because of its advantages of low cost, fast response time (speed), wide temperature range,  low power consumption, sunlight readable with transflective or reflective polarizers etc.  Most of them are monochrome LCD display and belong to passive-matrix LCDs.

TFT LCDs have capacitors and transistors. These are the two elements that play a key part in ensuring that the TFT display monitor functions by using a very small amount of energy without running out of operation.

Normally, we say TFT LCD panels or TFT screens, we mean they are TN (Twisted Nematic) Type TFT displays or TN panels, or TN screen technology. TFT is active-matrix LCDs, it is a kind of LCD technologies.

TFT has wider viewing angles, better contrast ratio than TN displays. TFT display technologies have been widely used for computer monitors, laptops, medical monitors, industrial monitors, ATM, point of sales etc.

Actually, IPS technology is a kind of TFT display with thin film transistors for individual pixels. But IPS displays have superior high contrast, wide viewing angle, color reproduction, image quality etc. IPS screens have been found in high-end applications, like Apple iPhones, iPads, Samsung mobile phones, more expensive LCD monitors etc.

Both TFT LCD displays and IPS LCD displays are active matrix displays, neither of them can produce color, there is a layer of RGB (red, green, blue) color filter in each LCD pixels to make LCD showing colors. If you use a magnifier to see your monitor, you will see RGB color. With switch on/off and different level of brightness RGB, we can get many colors.

Neither of them can’t release color themselves, they have relied on extra light source in order to display. LED backlights are usually be together with them in the display modules as the light sources. Besides, both TFT screens and IPS screens are transmissive, it will need more power or more expensive than passive matrix LCD screens to be seen under sunlight.  IPS screens transmittance is lower than TFT screens, more power is needed for IPS LCD display.

This display is designed for low power consumption and effective heat dissipation, making it durable for long-term usage in production facilities. It is the ultimate energy-efficient solution.

... master display unit with navigation buttons. The display is fully programmable for use in any machine application as a master controller. The IQAN-MD3 master display has a rugged mechanical ...

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TOPWAY Smart LCDs embed a display engine and a versatile range of TFT display module sizes and Touch-Panels to support a wide range of industrial and instrumentation ...

TOPWAY HMT101ATA-C is a Smart TFT display module with 32bit MCU on board. Its graphics engine provides numbers of outstanding features. It supports TOPWAY TML for preload and pre-design display ...

... device can perform multiple functions such as recording data when the recording function is activated. It comes with a bigger display and more I/O and logic channels than CMC-99. It is very compact in size as its case ...

... PN-HW displays. They offer a wide range of screen sizes and flexible installation methods, including standalone operation, making them the ideal choice for both retail and corporate organisations.

... PN-HW displays. They offer a wide range of screen sizes and flexible installation methods, including standalone operation, making them the ideal choice for both retail and corporate organisations.

... PN-HW displays. They offer a wide range of screen sizes and flexible installation methods, including standalone operation, making them the ideal choice for both retail and corporate organisations.

... integrated displays that offer a range of features from exceptionally high resolution in small format sizes to rugged, robust, 4K ready options with slim designs and fantastic readability.

TN screen has the advantages of stable performance and high reliability. TOPLAND can provide various sizes from 0.6 inch to 15 inch, and a variety of interfaces such as RGB / MCU / SPI / LVDS, ect.

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The wide range of conditions over which LCD monitors are used means that it is desirable to produce displays whose luminance (brightness) can be altered to match both bright and dim environments. This allows a user to set the screen to a comfortable level of brightness depending on their working conditions and ambient lighting. Manufacturers will normally quote a maximum brightness figure in their display specification, but it is also important to consider the lower range of adjustments possible from the screen as you would probably never want to use it at its highest setting. Indeed with specs often ranging up to 500 cd/m2, you will certainly need to use the screen at something a little less harsh on the eyes. As a reminder, we test the full range of backlight adjustments and the corresponding brightness values during each of our reviews. During our calibration process as well we try to adjust the screen to a setting of 120 cd/m2 which is considered the recommended luminance for an LCD monitor in normal lighting conditions. This process helps to give you an idea of what adjustments you need to make to the screen in order to return a luminance which you might actually want to use day to day.

Changing the display luminance is achieved by reducing the total light output for both CCFL- and LED-based backlights. By far the most prevalent technique for dimming the backlight is called Pulse Width Modulation (PWM), which has been in use for many years in desktop and laptop displays. However, this technique is not without some issues and the introduction of displays with high brightness levels and the popularisation of LED backlights has made the side-effects of PWM more visible than before, and in some cases may be a source of visible flicker, eyestrain, eye fatigue, headaches and other associated issues for people sensitive to it. This article is not intended to alarm, but is intended to show how PWM works and why it is used, as well as how to test a display to see its effects more clearly. We will also take a look at the methods some manufacturers are now adopting to address these concerns and provide flicker-free backlights instead. As awareness grows, more and more manufacturers are focusing on eye health with their monitor ranges.

Pulse Width Modulation (PWM) is one method of reducing the perceived luminance in displays, which it achieves by cycling the backlight on and off very rapidly, at a frequency you can’t necessary detect with the naked eye, but which could lead to eye issues, headaches etc. This method generally means that at 100% brightness a constant voltage is applied to the backlight and it is continuously lit. As you lower the brightness control the perceived luminance for the user reduces due to a number of possible controlling factors:

1) Frequency –The backlight is cycled on and off very rapidly, and this cycling typically occurs at a fixed frequency (in Hz). How fast this cycling occurs can impact whether flicker is visible or perceivable to the user, with higher frequencies being potentially less problematic. PWM has been known to operate at low frequencies of 180 – 240Hz for example which are likely to be more problematic than higher frequencies ranging up in to the Kilohertz range (e.g. 18,000Hz).

2) Modulation –The modulation of the cycling has an impact on the perceived brightness, and this describes the difference between the luminance in an “on” and in an “off” state. In some examples the backlight is completely turned off during the cycle so it is literally being turned on/off rapidly across the full brightness adjustment range. In those examples the luminance output is controlled really by the duty cycle only (see point 3). In other examples the backlight is not always being completely turned off but rather the voltage applied to the backlight is being rapidly alternated, resulting in less extreme differences between the on and off states. Often this modulation will be narrow in the high brightness range of the display, but as you reduce further, the modulation becomes wider until it reaches a point where the backlight is being switched completely off. From there, the change in the duty cycle (point 3) controls the further changes in the luminance output.

3) Duty Cycle – The fraction of each cycle for which the backlight is in an “on” state is called the duty cycle. By altering this duty cycle the total light output of the backlight can be changed. As you reduce the brightness to reach a lower luminance, the duty cycle becomes progressively shorter, and the time for which the backlight is on becomes shorter, while the time for which it is off is longer. This technique works visually since cycling the backlight on and off sufficiently fast means the user cannot see this flickering, because it lies above their flicker-fusion threshold (more on this later).

Above we can see graphs of a backlight’s output using “ideal” PWM for several cycles. The maximum output of this backlight in the example is 100 cd/m2, and the perceived luminance for the 90%, 50% and 10% cases are: 90, 50 and 10 cd/m2 respectively. The modulation percentage is the ratio between the minimum and maximum luminance during the cycle, and is 100% here, so it is being completely turned on and off. Note that during the duty cycle the backlight is at its maximum luminance.

The analogue (non-PWM) graphs corresponding to these perceived luminance levels would appear as shown below. In this case there is no modulation. This is the method used for flicker-free backlights which we will discuss more a little later.

The main reasons for the use of PWM is that it is simple to implement, requiring only that the backlight can be switched on and off rapidly, and also gives a large range of possible luminance.

The luminance of LED backlights can be adjusted greatly by altering the current passing through them, though this has the effect of altering the colour temperature slightly. This analogue approach to LED luminance is also undesirable since the accompanying circuits must take into account the heat generated by the LED’s. LED’s heat up when on, which reduces their resistance and further increases the current flowing through them. This can quickly lead to runaway current use in very high-brightness LED’s and cause them to burn out. Using PWM the current can be forced to hold a constant value during the duty cycle, meaning the colour temperature is always the same and current overloads are not a problem.

While PWM is attractive to hardware makers for the reasons outlined above, it can also introduce distracting visual effects if not used carefully. Flicker from LED backlights is typically much more visible than for older CCFL backlights at the same duty cycle because the LED’s are able to switch on and off much faster, and do not continue to “glow” after the power is cut off. This means that where the CCFL backlight showed rather smooth luminance variation, the LED version shows sharper transitions between on and off states. This is why more recently the subject of PWM has cropped up online and in reviews, since more and more displays are moving to W-LED backlighting units now.

It is important to remember that this is entirely due to the backlight, and the display itself is showing a static image. Often it is said that humans cannot see more than 24 frames per second (fps), which is not true and actually corresponds to the approximate frame rate needed to perceive continuous motion. In fact, while the eyes are moving (such as when reading) it is possible to see the effects of flicker at several hundred hertz. The ability to observe flicker varies greatly between individuals, and even depends on where a user is looking since peripheral vision is most sensitive.

It is also important to distinguish the difference between flicker in CRT displays and CCFL and LED backlit TFT displays. While a CRT may flicker as low as 60Hz, only a small strip is illuminated at any time as the electron gun scans from top to bottom. With CCFL and LED backlit TFT displays the entire screen surface illuminates at once, meaning much more light is emitted over a short time. This can be more distracting than in CRTs in some cases, especially if short duty cycles are used.

The flicker itself in display backlights may be subtle and not easily perceptible for some people, but the natural variation in human vision seems to make it clearly visible to others. With the use of high-brightness LED’s on the rise it is becoming increasingly necessary to use short PWM duty cycles to control brightness, making flicker more of a problem. With users spending many hours every day looking at their monitors, shouldn’t we consider the long term effects of both perceptible and imperceptible flicker?

If you find PWM backlight flickering distracting or just want to see if reducing it makes reading on a monitor easier, I’d encourage you to try the following: Turn the brightness of your monitor up to maximum and disable any automatic brightness adjustments. Now use the colour correction available in your video card drivers or calibration device to reduce the brightness to normal levels (usually by adjusting the contrast slider). This will reduce the luminance and contrast of your monitor while leaving the backlight on as much as possible during PWM cycles. While not a long-term solution for most due to the decreased contrast, this technique can help to discover if a reduction in PWM usage is helpful.

A much better method of course would be to purchase a display not relying on PWM for dimming, or at least one which uses a much higher cycling frequency. Few manufacturers seem to have implemented PWM at frequencies that would limit visible artefacts (well above 500Hz for CCFL and above 2000 Hz for LED). Additionally, some displays using PWM do not use a 100% duty cycle even at full brightness, meaning they will always produce flicker. Several LED-based displays may in fact be currently available which do not use PWM, but until backlight frequency and modulation become listed in specifications it will be necessary to see the display in person. Some manufacturers promote “flicker free” monitors in their range (BenQ, Acer for example) which are designed to not use PWM at all and instead use a Direct Current (DC) method of backlight dimming. Other manufacturers such as Eizo talk about flicker free backlights but also list a hybrid solution for their backlight dimming, where PWM is used for some of the brightness adjustment range at the lower end. In fact it seems an increasingly common practice for a screen to be PWM free down to a certain point, and then fro PWM to be used to really drive down the minimum luminance from there.

An easy method of measuring the PWM frequency of a backlight would be ideal, and luckily it can be done using only a camera which allows manual control of the shutter speed. This can quickly and easily identify PWM frequencies in the lower range, but may not be suitable for high frequency PWM. It should be able to detect PWM up to at least 500Hz though, but anything above that may look like a solid block, suggesting no use of PWM, when in fact it might be just using a higher frequency. Further more complex methods such as our oscilloscope setup would be needed to validate flicker-free status for definite.

(Optional) Set the camera white balance by getting a reading off the screen while displaying only white. If not possible, then manually set the white balance to about 6000K.

Display a single vertical thin white line on a black background on the monitor (1-3 pixels wide should be fine). The image should be the only thing visible. Here is an example you may wish to save and use, show it full screen on your monitor.

Set the camera to use a shutter speed of 1/2 to 1/25 of a second. You may need to set the ISO sensitivity and aperture in order to capture enough light. Make sure the line is in focus at the distance you are holding it (lock the focus if needed).

Hold the camera about 2 feet in front of the monitor and perpendicular to (looking straight at) the front. Press the shutter button as you slowly move it horizontally across the screen (remaining perpendicular). You may need to experiment with moving the camera at different speeds.

Multiply this count by the inverse of the shutter speed. For example, if using a shutter speed of 1/25 of a second and 7 cycles are counted, then the number of cycles per second is 25 * 7 = 175Hz. This is the backlight cycle frequency.

What we are doing with this technique is turning a temporal effect into a spatial one by moving the camera during capture. The only significant source of light during the image capture is the thin line on the display, which is exposed onto consecutive columns on the sensor. If the backlight is flickering, different columns will have different brightness or colour values determined by the backlight at the time it was exposed.

A common problem when first attempting this technique is that the image is too dark. This can be mitigated by using a larger camera aperture (lower f/number) or increasing the ISO value. The shutter speed is not a factor in the exposure since we are using it only to control the total exposure time. The brightness of the image can also be adjusted by changing the speed at which the camera is moved, with a fast speed giving a darker image and more temporal resolution and a slow speed a brighter image with lower resolution. Another problem encountered is unevenly-spaced cycles in the final image, which is caused by the camera changing speed during exposure. Continuing to move the camera before and after the exposure helps to steady this. An image which looks particularly smooth may be due to it being out of focus. This can sometimes be helped by pressing the shutter button halfway to focus on the line target, then proceeding as normal.

Depending on the monitor several additional effects may be visible. CCFL-based backlights often show different colours at the start and end of each cycle, which means the phosphors used respond at different rates. LED-based backlights often use a higher cycling frequency than CCFL-based, and more rapid camera movement may be needed to easily see them. Dark stripes between cycles mean that the PWM duty cycle has been reduced to such an extent that no light is emitted for part of the cycles.

Using our oscilloscope and photosensor equipment it is possible to measure the PWM frequency and patterns far more accurately. While the above photo method is certainly suitable for a casual user, an oscilloscope can reveal more detail about the PWM operation and will be featured in all our reviews moving forward. We measure the luminance output of the screen at brightness settings of 100, 50 and 0%. This allows us to easily identify the backlight dimming technique, and if PWM is being used we can work out its frequency and comment on modulation, duty cycle etc.

Asus PA248Q – W-LED backlight. At 100% brightness we see a constant luminance output and a straight line, as there is no need for the backlight to be cycled. At 50% you can see PWM controls the backlight on and off. The modulation is always 100%, but the luminance reduction is controlled by the duty cycle which becomes progressively shorter. You can see much shorter “on” peaks in the 0% brightness graphs. We measure the frequency at 180Hz which is fairly typical.

The oscillographs for a typical CCFL display using PWM at 0% looks like the above. You can see the transitions from on to off are less sudden as the phosphors don’t go dark as quickly as with LED backlight units. As a result, the use of PWM may be less problematic to users.

As we said at the beginning, this article is not designed to scare people away from modern LCD displays, rather to help inform people of this potential issue. With the growing popularity in W-LED backlit monitors it does seem to be causing more user complaints than older displays, and this is related to the PWM technique used and ultimately the type of backlight selected. Of course the problems which can potentially be caused by the use of PWM are not seen by everyone, and in fact I expect there are far more people who would never notice any of the symptoms than there are people who do. For those who do suffer from side effects including headaches and eye strain there is an explanation at least.

With the long term and proven success of a technology like Pulse Width Modulation, and the many years of use in CCFL displays we can’t see it being widely changed at any time soon to be honest, even with the popular move to W-LED backlit units. It is still a reliable method for controlling the backlight intensity and therefore offering a range of brightness adjustments which every user would want and need. Those who are concerned about its side effects or who have had problems with previous displays should try and consider the frequency of the PWM in their new display, or perhaps even try and find a screen where it is not used at all in backlight dimming. Some manufacturers are proactively addressing this concern through the use of flicker free backlights, and so options are emerging which do not use PWM.

Before you get a new monition for your organization, comparing the TFT display vs IPS display is something that you should do. You would want to buy the monitor which is the most advanced in technology. Therefore, understanding which technology is good for your organization is a must. click to view the 7 Best Types Of Display Screens Technology.

Technology is changing and becoming advanced day by day. Therefore, when you are looking to get a new monitor for your organization, LCD advantages, and disadvantage,  you have to be aware of the pros and cons of that monitor. Moreover, you need to understand the type of monitor you are looking to buy.

That is why it is important to break it down and discuss point by point so that you can understand it in a layman’s language devoid of any technical jargon. Therefore, in this very article, let’s discuss what exactly TFT LCDs and IPS LCDs are, and what are their differences? You will also find out about their pros and cons for your organization.

The word TFT means Thin-Film-Translator. It is the technology that is used in LCD or Liquid Crystal Display. Here you should know that this type of LCD is also categorically referred to as active-matrix LCDs. It tells that these LCDs can hold back some pixels while using other pixels. So, the LCD will be using a very minimum amount of energy to function. TFT LCDs have capacitors and transistors. These are the two elements that play a key part in ensuring that the display monitor functions by using a very small amount of energy without running out of operation.

Now, it is time to take a look at its features that are tailored to improve the experience of the monitor users significantly. Here are some of the features of the TFT monitor;

The display range covers the application range of all displays from 1 inch to 40 inches as well as the large projection plane and is a full-size display terminal.

Display quality from the simplest monochrome character graphics to high resolution, high color fidelity, high brightness, high contrast, the high response speed of a variety of specifications of the video display models.

No radiation, no scintillation, no harm to the user’s health. In particular, the emergence of TFT LCD electronic books and periodicals will bring humans into the era of a paperless office and paperless printing, triggering a revolution in the civilized way of human learning, dissemination, and recording.

It can be normally used in the temperature range from -20℃ to +50℃, and the temperature-hardened TFT LCD can operate at low temperatures up to -80 ℃. It can not only be used as a mobile terminal display, or desktop terminal display but also can be used as a large screen projection TV, which is a full-size video display terminal with excellent performance.

The manufacturing technology has a high degree of automation and good characteristics of large-scale industrial production. TFT LCD industry technology is mature, a mass production rate of more than 90%.

It is a perfect combination of large-scale semiconductor integrated circuit technology and light source technology and has great potential for further development.

TFT LCD screen from the beginning of the use of flat glass plate, its display effect is flat right angles, let a person have a refreshing feeling. And LCDs are easier to achieve high resolution on small screens.

The word IPS refers to In-Plane-Switching which is a technology used to improve the viewing experience of the usual TFT displays. You can say that the IPS display is a more advanced version of the traditional TFT LCD module. However, the features of IPS displays are much more advanced and their applications are very much widespread. You should also know that the basic structure of the IPS LCD is the same as TFT LCD if you compare TFT LCD vs IPS.

As you already know, TFT displays do have a very quick response time which is a plus point for it. But, that does not mean IPS displays a lack of response time. In fact, the response time of an IPS LCD is much more consistent, stable, and quick than the TFT display that everyone used to use in the past. However, you will not be able to gauge the difference apparently by watching TFT and IPS displays separately. But, once you watch the screen side-by-side, the difference will become quite clear to you.

The main drawback of the TFT displays as figured above is the narrow-angle viewing experience. The monitor you buy for your organization should give you an experience of wide-angle viewing. It is very much true if you have to use the screen by staying in motion.

So, as IPS displays are an improved version of TFT displays the viewing angle of IPS LCDs is very much wide. It is a plus point in favor of IPS LCDs when you compare TFT vs IPS. With a TFT screen, you cannot watch an image from various angles without encountering halo effects, blurriness, or grayscale that will cause problems for your viewing.

It is one of the major and remarkable differences between IPS and TFT displays. So, if you don’t want to comprise on the viewing angles and want to have the best experience of viewing the screen from wide angles, the IPS display is what you want. The main reason for such a versatile and wonderful viewing angle of IPS display is the screen configuration which is widely set.

Now, when you want to achieve wide-angle viewing with your display screen, you need to make sure it has a faster level of frequency transmittance. It is where IPS displays overtake TFT displays easily in the comparison because the IPS displays have a much faster and speedier transmittance of frequencies than the TFT displays.

Now the transmittance difference between TFT displays and IPS displays would be around 1ms vs. 25ms. Now, you might think that the difference in milliseconds should not create much of a difference as far as the viewing experience is concerned. Yes, this difference cannot be gauged with a naked eye and you will find it difficult to decipher the difference.

However, when you view and an IPS display from a side-by-side angle and a TFT display from a similar angle, the difference will be quite evident in front of you. That is why those who want to avoid lagging in the screen during information sharing at a high speed; generally go for IPS displays. So, if you are someone who is looking to perform advanced applications on the monitor and want to have a wider viewing angle, then an IPS display is the perfect choice for you.

As you know, the basic structure of the IPS display and TFT displays are the same. So, it is quite obvious that an IPS display would use the same basic colors to create various shades with the pixels. However, there is a big difference with the way a TFT display would produce the colors and shade to an IPS display.

The major difference is in the way pixels get placed and the way they operate with electrodes. If you take the perspective of the TFT display, its pixels function perpendicularly once the pixels get activated with the help of the electrodes. It does help in creating sharp images.

But the images that IP