Segment drive method:
Used for simple displays, such as those in calculators
Dot-matrix drive method:
Used for high-resolution displays, such as those in portable computers and TFT monitors.
Two types of drive method
Simple driving method:
In the static, or direct, drive method, each pixel is individually wired to a driver.
Multiplex drive method:
As the number of pixels is increased, the wiring becomes very complex, we used this alternative method, in which the pixels are arranged and wired in a matrix format.
Passive and Active Matrix LCDs
Passive Matrix (AMLCDs) :
There are no switching devices, and each pixel is addressed for more than one frame time. The effective voltage applied to the LC must average the signal voltage pulses over several frame times, which results in a slow response time of greater than 150 msec and a reduction of the maximum contrast ratio.
Active-matrix LCDs (AMLCDs) :
A switching device and a storage capacitor are integrated at the each cross point of the electrodes. There are many kinds of AMLCD. For their integrated switching devices most use transistors made of deposited thin films, which are therefore called thin-film transistors (TFTs).
The most common semiconducting layer is made of amorphous silicon (a-Si).
Passive Matrix
- Row & Column approach
- Apply small bias to perpendicular lines of electrodes
- Bias strong enough to darken bit at line intersection
- Multiplexed addressing scheme
- Advantage: Simple to implement
- Disadvantage: Can cause distortion (‘ghosting’ or ‘crosstalk’)
Active Matrix
- Each cell has its own thin-film transistor (TFT)
- Addressed independently from behind LCD
- Direct addressing scheme
- Advantages: Sharp display, better viewing angle, 40:1 contrast
- Disadvantages: Need better backlight, complex hardware
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