|Technical Info. - LCD Technologies|
Twisted Nematic (TN) LCD consists of a layer of liquid crystal
material supported by two glass plates. The liquid crystal material is a
mixture of long, cylindrically shaped molecules with different electrical
and optical properties, depending on direction
the outer surface of the glass plates, polarizers are placed so they are
parallel to the liquid crystal orientation and perpendicular to each
other. in the "off" state, light entering the first polarizer is
guided by the liquid crystal layer twist to the second polarizer, through
which it is transmitted. When the cell is energized, the LC material is
aligned with the electric field; light transmitted through the first
polarizer is blocked by the second polarizer, forming a dark image. The
effect may be reversed if the polarizers are placed parallel to each
other, and a light image on a dark background is formed
Twisted Nematic LCD's have a twist that is greater than 90 but less than
360 degrees. Currently most STN displays are made with a twist between 180
and 270 degrees. The higher twist angles cause steeper threshold curves
which put the on and off voltages closer together. The steeper thresholds
allow multiplex rates greater than 32 to be achieved.
addition to normal supertwist displays, there also exist double
supertwist and triple supertwist displays. In general, the more
twists, the higher the contrast.
Supertwist displays are
also known as supertwist nematic (STN) displays.
most recent advance has been the introduction of Film compensated Super
Twisted Nematic (FSTN) displays. This adds a retardation film to the STN
display that compensates for the color added by the birefringence effect.
This allows a black and white display to be produced and provides for a
higher contrast and wider viewing angle.
for color super-twist nematic,
an LCD technology developed by Sharp Electronics Corporation. Unlike TFT ,
CSTN is based on a passive-matrix , which is less expensive to produce. The original CSTN
displays developed in the early 90's suffered from slow response times and
ghosting. Recent advances in the technology, however, have made CSTN a
viable alternative to active-matrix displays. New CSTN displays offer 100
response times, a 140 degree viewing angle, and high-quality color
rivaling TFT displays - all at about half the cost.
Short for double-layer
supertwist nematic, a passive-matrix LCD technology that uses two display layers
to counteract the color shifting that occurs with conventional supertwist
Short for thin film transistor, a type of LCD flat-panel display screen, in which each pixel is controlled by from one to four transistors. The TFT technology provides the best resolution of all the flat-panel techniques, but it is also the most expensive. TFT screens are sometimes called active-matrix LCDs.