TN ,STN LCD, FSTN LCD Display Technology

This article introduce TN LCD and stn lcd display technologies, what are the difference between TN and STN LCD, FSTN and FFSTN LCD technology. How do TN LCD and STN LCD display work. let's see the introduction on the following:

How many types of LCD are available?

There are monochrome lcd and color LCD types.

Monochrome LCD technologies are including TN LCD, HTN, STN LCD (yellow-green mode, blue mode, gray mode, black-white mode/FSTN,FFSTN), monochrome tft lcd technology.

Color LCDs are including color STN LCD and color TFT LCD types （α-Si TFT and IPS TFT LCD). TFT LCD technology has definitely advantages than color STN LCD, color STN LCD (CSTN lcd) technology has been almost phased out in the market, all CSTN LCDs have been replaced by tft lcd displays nowadays.

In this article, we only introduce monochrome LCD display technogy. First, let's see:

What is TN LCD?

TN LCD means (twisted nematic) LCD, the namatic liquid crystal elements inside the lcd glass cell,its twisted angle is 90 degree, integrated the front and rear polarizes on the lcd, the polarized angle is also in 90 degree in cross, it control the light transmission and make the tn LCD display on and off.

TN LCD technoly is used for segments display in monochrome LCD displays, that the display content only have small quantity segments. total common lines less than 8 commons maximum, that it is 1/8 duty in the driving mode.

HTN LCD Displays:

HTN LCD(High-Temperature Nematic,twisted angle: 110°) offer a wider viewing angle than TN LCD displays, making them ideal for applications that require wider viewing angle than TN display, lower power consumption and more commons pins in LCD driving. HTN LCD technology is between TN LCD and STN LCD, it is better than TN LCD in contrast and viewing, but less than STN LCD in these performances.  HTN could drive the common lines up to 16 commons. while TN LCD can not drive the common lines up to 8.

What is STN LCD?

STN lcd is super-twisted nematic lcd display, it is a type of monochrome lcd display, it is also passive liquid crystal display (LCD). STN LCD twist angle is 240 degree, instead of 90 degree as TN LCD, so we call it STN LCD. STN lcd have yellow-green display mode, gray,black-white mode, blue display mode, available.

The STN LCD is not only difference on twist angle in 240 °, in the same time, because the liquid crystal has the double-reflective characteristic, the ambient light through the polarizer, it would change to linear polarized light, the linear polarized light go through the STN LCD cell with 240° twist angle, it would turn to oval polarized light because of the double-reflective of liquid crystal characteristic （the linear polarized light turn to two group lights via 240° twist angle liquid crystal, and the two group light intervened to oval polarized light）. the oval polarized lights are always with colors, that that is the reason of yellow-green or blue color come from for the STN LCD.

What is FSTN LCD?

FSTN lcd display mode is the profession name for black-white STN LCD mode, it is white background and black display characters. it is the nearest color to paper in monochrome lcd, even its real background is a little near to gray. FSTN LCD mode is one of STN mode, it is mean film STN, instead of the background color to yellow-green color or blue color, FSTN LCD add a optics compensating film on the front of FSTN LCD, the optics compensating  film compensate the linear polarize light and color from STN LCD, the STN LCD color turn to white background after light through the optics compensator film. that is the compensating film turn the oval polarized light to the linear polarized light again, then we could get the white and black lcd display. it is the display mode that near to paper. FSTN lcd is widely used in many display application because of its background.

STN, FSTN, FFSTN LCD (DFSTN LCD) structure:

What is FFSTN LCD?

FFSTN is FSTN LCD in negative display mode, it is also called DFSTN, means double films STN, it is also a kind of white-black STN LCD mode, FFSTN lcd is negative background with white display characters, while FSTN lcd is white background with black characters, its background would be in black, and display white characters. FSTN lcd would need one layer polarized light compensation, FFSTN would need two layers polarized light compensation on the front and rear polarizers, it would need higher cost than other STN LCD, but FFSTN LCD is best lcd soluton in STN LCD. it is higher contrast than other types of lcd.

CSTN LCD technology:

CSTN lcd means color STN LCD, its display technology is based on FFSTN mode, but it have a RGB color filter in side the lcd glass, so it can realize to color display, and because FFSTN have high contrast, so instead lcd font display to other STN LCD, CSTN LCD is better in image display than other monochrome lcd. but CSTN lcd is still type of stn lcd, it have cross-talk effect, which decreased the contrast than TFT LCD which is active display mode without cross-talk.

TN LCD and TFT :

TFT (thin film transistor) is still one kinds of lcd, but it active matrix lcd which without cross-talk with higher contrast than STN LCD or monochrome TN LCD. because of the thin film transistor inside, it is without cross-talk problem, and easily to get the high contrast. besides IPS tft, most of tft lcd is still TN LCD display mode, that is 90 degree twist angle to the liquid crystal.

Which is better: STN LCD vs TN LCD

Because STN lcd display is 240 degree twist angle, it have better display contrast than TN display in 90 degree twist angle. the STN display could support the 1/240 duty lcd, that with 480 segment x240 common graphic lcd. and the TN lcd only support 1/8 duty with 8 commons maximum. so TN lcd is mainly used in segment lcd display or icon lcd display. STN display is mainly used in graphic lcd display. of course, if STN lcd is also can be used segment lcd display or icon lcd display, but its cost would be around double than TN lcd display.

Contrast and viewing angle: STN LCD vs TN LCD:

With the twist angle in 240°, it bring higher display contrast as the twist angle from TN 90° to STN 240°, as see the graph as below, as the increasing about the lcd contrast in twist angle, when TN lcd can support 8 commons driver (1/8 duty), such as segment lcd, because the TN liquid crystal sharpness is less than STN LCD, if the commons higher than 8, the TN lcd contrast would be decreased dramatically. while STN lcd could support 240 commons (1/240 duty) in maximum. STN not only support 16x2, 20x4 characters lcd, and could support 128x64, 320x240 graphic lcd as well, it is all because the contrast increased due to liquid crystal's twist angle for STN lcd.

Meanwhile, as the display contrast increased for the STN LCD, it bring wider viewing angle for STN lcd than TN lcd display. STN lcd viewing angle could be reach 120 degree, while TN lcd viewing angle around 90 degree.

STN LCD vs TFT LCD

STN LCD display require less power and are less expensive to manufacture than TFT LCDs, STN displays typically has lower image quality and slower response time compare than TFT displays. and tft lcd display is mainly in color display, but STN LCDs have the advantage that it can be made purely reflective for viewing under direct sunlight. STN LCD is a good choice for sunlight readable display in outdoor, for it has a display effect in outdoor and less power consumption. such as transflective STN lcd or reflective STN LCD,they can display well without backlight light on.

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