Liquid Crystal Display (LCD) screen is characterized by small size, thin, lightweight, energy-efficient, wide viewing angle, no flicker, and can be directly matched with CMOS integrated circuit, which makes it dominant in the display world.
According to the
display technology
, there are many different types of LCDs, including TN, STN, TFT, IPS, etc. How do they work, and what&#;s the difference between them?
TN (Twisted Nematic) LCD is a kind of monochrome LCD display technology that can be used as a positive or negative display mode. It contains two polarized filters, and nematic liquid crystal elements that are inside two glass substrates. When nature's light goes through the front polarizer to meet with the nematic liquid crystal cells, it twists 90-degree, and passes through the rear glass to arrive at the rear polarizer. In this way, it controls the TN LCD panel on and off, and lets us see the light. As one of the oldest LCD display technologies, it has lower cost, and faster response time, but suffers from limited viewing angle, so it is mostly used in the low-end market, such as LCD panel terminals.
STN (Super Twisted Nematic) LCD is characterized by the use of passive-matrix monochrome pixels. It differs from TN LCDs only in the twisted composition as it uses a 180-to-190-degree twisted composition for its pixel. STN LCDs produce sharper contrast, and require less power, but they are more expensive and have slower response speed than TN LCDs. They are typically used in inexpensive mobile phones and digital information display screens.
TFT (Thin Film Transistor) LCD is one of active matrix LCD that uses thin-film transistor technology to create images and improve image quality. The liquid crystal molecules are filled between two parallel glasses. Two polarizer filters, color filters (RGB, red/green/blue), and two alignment layers decide the amount of light that is allowed to pass and which colors are created. TFT LCDs have excellent performance with minimal energy consumption, faster and more accurate response time, and sharp visibility. Thanks to TFT technology, it makes more display devices possible like televisions, laptop
monitors
, CDs, DVDs, etc., and also makes the world more colorful.
IPS (supper fine TFT) LCD is a variant of TFT LCDs that have liquid crystals to switch in and out of a plane, which leads it to reign supreme in regards to the great color performance and ultra-wide viewing angles. Whereby, IPS LCD panels become the preferred choice of those who value image quality and super-wide viewing angles, such as professional applications dealing with graphics, monitors for gaming, high-level business use, etc.
Although there are many kinds in the LCD panel technology family, and they might get things confusing, you still can find the best for your needs.
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There are many LCD display types to choose from. Some are new cutting edge technology and other are older legacy types of displays. Although even some of the legacy type of LCD displays make use of cutting edge technology. The goal of this article is to provide the reader with a brief overview of the uses, advantages and disadvantages of each type of display.
Segment LCD&#;s, also called static or direct drive are an older technology but are still in heavy use today. These displays are reliable and have been in use for many years. They show no signs of going away anytime soon.
The goal of this display is simplicity. Their only job is to display letters, numbers and icons. There is no 3-D effect or range of brilliant colors and most do not contain a touch screen or any other type of human interface. They normally are not equipped wit a controller/driver chip.
In fact, you could reduce the static/direct drive LCD down to the simple formula of one pin equals one segment. If you need a display that contains a 7 segment number, you need 7 pins. The exception to this is if you increase the number of backplanes and convert this to a multiplex display.
The formula for a multiplex display is a little more complicated. One pin equals 2 or 4 segments. The advantage of multiplexing is that you reduce the number of pins which, in turn, reduces the cost of the display and the amount of time required to mount the display to a PCB.
One disadvantage of multiplex display over direct drive displays is that the refresh rate is slower and this may allow the segments that are ON to &#;fade&#; or not look as sharp. Some times this is referred to as &#;ghosting&#;. This is not a very common occurrence as the technology has improved since the days of pagers and low cost calculators.
When a customer cannot decided what LCD display type to use we have a general rule: If the total number of segments is 20 or less, we advise a static (direct drive) display since a display with 20 pins is low cost to build and to install on the PCB.
Once the number of segments exceed 20, we recommend multiplex. A display with more than 120 segments becomes cost prohibitive.
If your design exceeds 120 segments we would recommend converting your design to a graphics type of LCD display that makes use of the controller driver chip. The controller driver chip allow the number of connections for multiple segments to be reduced to 14 or 16 pins. This LCD technology is covered later in the article.
While monochrome displays are simple and can come across as somewhat boring, there are some key advantages to consider when choosing which of the LCD display types to go with.
Low Power LCD Displays
One key advantage of the monochrome LCD display is that they are not power hungry. They operate with very little current draw. This becomes an ideal choice when the only power you have is a battery. These displays are built to operate at 3.0V, 3.3V (in some case they can operate as low as 1.7V) and 5V. The current draw for a display with no backlight can run as low as 6uA per cm^2. (Note: The lower the operating temperature of the LCD, the greater the power required).
If all you need to display is what time it is, the current temperature, or the number of gallons, and your customer does not wish to pay for vibrant, flashy power-hungry color, then this display will work perfectly for you.
Customizable LCD Displays
The majority of the static or multiplex displays we offer have been customized to meet the customer&#;s requirements. This is a great advantage to consider when choosing one of the LCD display types you will use in your product.
A customized static or multiplex display allows you to have the display built to the dimensions you require. You can select the following options:
The tooling or NRE (non-recurring engineering cost) of this type of display is much lower than newer technologies and the MOQ (minimum order quantities) are also lower than other types of displays.
If your goal is to display basic information, with a low tooling cost and you need to operate on a low power budget than the best type of LCD Display is a static or multiplex LCD.
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