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Other Optical Effects
Published in Mary Anne White, Physical Properties of Materials, 2018
The terms passive-matrix and active-matrix refer to the way in which each pixel in the LCD is activated. In the passive-matrix mode, a row and a column in a grid supply voltage to the pixel at their intersection point. Active-matrix LCDs address a particular pixel by switching on the row and then sending a charge down the correct column; at the intersection, a thin-film capacitor can be carefully charged and the pixel activated. Although the passive-matrix device is simpler, it has the disadvantage of slow response time and ghost images on neighboring pixels, reducing resolution. These disadvantages are overcome with the active-matrix approach, but they are somewhat more complex (and expensive) to produce.
Circuit Components
Published in Julio Sanchez, Maria P. Canton, Microcontroller Programming, 2018
Julio Sanchez, Maria P. Canton
One way of reducing the number of electrical connections in an LCD is by means of a method called passive matrix display. Here the pixels to be lighted are determined by the crossing points between the row and the column selector electrodes. For example, in the 5 × 7 matrix display in Figure 6-34, the pixel at the center of the character is selected by picking row number 4 and column number 3. The name passive matrix originates in the fact that each pixel must retain its state between refreshes. As the number of pixels to be refreshed increases so does the time required for the refresh cycle. As a consequence of their design, passive matrix displays usually have slow response times and poor contrast.
Organic electroluminescent displays
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
A passive matrix is the simplest possible matrix display and consists of arrays of rows and columns forming pixels where they intersect. One row is selected and all the pixels on that row are driven from the columns. The other rows are selected in turn until the entire frame has been scanned. From their inception OLEDs were, due to their diode nature, touted as ideal for the fabrication of passive matrix displays, with visions of huge screens for very low cost. Of course, life is never that simple. As we shall see, the size of a passive matrix display is limited by the peak current required for pulsed light emission, by current leakage and, in particular, by the effects of device capacitance.
Enhanced electro-optical response of nematic liquid crystal doped with functionalised silver nanoparticles in twisted nematic configuration
Published in Liquid Crystals, 2020
Shivaraja S J, R K Gupta, Sandeep Kumar, V Manjuladevi
The increasing steepness of V–T curve is necessary for better multiplexing performance which can be easily achieved by increasing twist angle of the LC layer in case of super twisted nematic liquid crystal (STN) mode. The steepness of V–T curve also depends on the values of bend to splay elastic constant ratio (K33/K11) and the dielectric ratio , where Δε is the dielectric anisotropy and is perpendicular component of dielectric constant. Larger bend to splay elastic constant ratio is essential for high multiplexing rates with STN displays, whereas low value of this ratio is required for TN displays. Small dielectric ratio is required for steeper V–T curve. A steep V–T curve and well-defined optimum threshold voltage are a prerequisite to achieve high contrast passive matrix displays capable of binary or grey levels in applications requiring a high information content [43–45]. The steepness of V–T curve increases by 166%, 230%, 213%, 57% and 10% for 0.015 wt%, 0.025 wt%, 0.05 wt%, 0.1 wt% and 0.2 wt% of f-AgNPs in 5PCH, respectively, compared to pure 5PCH. The increase in the steepness of V–T curve in the f-AgNPs doped nanocomposites of 5PCH might be due to the decrease of ratio [30]. The increase in steepness may also be due to the decrease of visco-elastic ratio.