摘要:
A ferroelectric liquid crystal display comprises a layer of ferroelectric liquid crystal material contained between two cell walls, surface treated to align the material in a tilted layer. The walls carry eg row and column electrodes forming an x,y matrix of addressable elements or pixels. Multiplex addressing voltages are provided by driver circuits. An improved addressing is obtained by varying the addressing voltage applied during switching of a pixel to maximize torque applied on liquid crystal molecules. Addressing voltages are from two data waveforms and one strobe waveform; the data waveforms have more than two voltage levels, dc balance, and equivalent rms. values; the strobe waveform has two or more voltage levels (which may include a zero level). The strobe and data waveforms combine to provide a resultant voltage that form an addressing voltage at each pixel.
摘要:
A ferro-electric liquid crystal display is multiplex addressed by strobe waveform applied in sequence to each electrode in one set of electrodes coincidently with data waveforms applied to a second set of electrodes. Liquid crystal material in the display is switched by a d.c. pulse of appropriate polarity, amplitude and time. The strobe waveforms have first and second pulse pairs, each pulse pair comprising two pulses of different amplitude and the same or different sign. The pulse pairs are similar but of opposite sign. Data waveforms are rectangular waveforms of opposite sign. The amplitude and ratio of leading pulse to trailing pulse in each strobe pulse pair are adjusted to obtain the desired switching and contrast. Compensation for temperature changes is arranged by measuring the temperature of the liquid crystal material and using the value obtained to adjust the amplitude value of the leading pulse in each strobe pulse pair.
摘要:
A ferro-electric liquid crystal display is multiplex addressed by blanking and strobe waveforms applied in sequence to each electrode in one set of electrodes coincidentally with data waveforms applied to a second set of electrodes. Liquid crystal material in the display is switched by a d.c. pulse of appropriate polarity, amplitude and time. The strobe waveforms have a pulse pair comprising two pulses of different amplitude and the same or different sign. Data waveforms are rectangular waveforms of opposite sign. The amplitude and ratio of leading pulses to trailing pulses in each strobe pulse pair are adjusted to obtain the desired switching and contrast. Compensation for temperature changes is arranged by measuring the temperature of the liquid crystal material and using the value obtained to adjust the amplitude value of the leading pulse in each strobe pulse pair.
摘要:
The invention provides an addressing scheme with temperature compensation for temperature induced changes in liquid crystal material switching parameters. Temperature compensation is provided by measuring liquid crystal temperature, and varying the length of strobe waveforms accordingly. A ferroelectric liquid crystal cell is addressed by row and column electrodes forming an x,y matrix of display elements. A strobe waveform is applied to each row in sequence whilst appropriate data waveforms are applied to all the column electrodes. At each display element, the material receives an addressing waveform to switch it to one of its two switched states depending upon the polarity of the addressing waveform. The data waveforms are, e.g., alternating positive and negative pulses of period 2 ts. The strobe waveform has a zero for one time period ts followed by a unipolar voltage pulse of significant duration, e.g., equal to or greater than 0.25 ts or more. This may result in an overlapping of addressing in adjacent rows, e.g., the end of a strobe pulse on one row overlaps with the beginning of a strobe pulse on the next row. The display elements may be switched into one of their two states by one of two strobe pulses of opposite polarity. Alternatively, a blanking pulse may switch all elements to one state and a strobe used to switch selected elements to the other state.
摘要:
The invention provides a ferro-electric liquid crystal display (FLCDs) with reduced voltages requirements for driver circuits. This enables standard drivers circuits designed to rms address twisted nematic type of displays, to be used for FLCDs. Displays are formed by cells containing smectic liquid crystal material. The cell walls are surface treated and carry e.g. row and column electrodes forming an x,y matrix of addressable display elements. The smectic liquid crystal material switches between two states upon application of a dc pulse of appropriate amplitude, polarity, and time. Addressing waveforms are strobe waveforms, e.g. two pulses of opposite polarity in successive time slots, applied to each row in turn. Data waveforms are, e.g. dc pulses of alternate polarity with each pulse lasting one time slot ts. Two data waveforms are needed to switch between the two states; one data waveform is the inverse of the other. Typically a strobe waveform pulse may be 50 volts. In the invention a voltage reduction waveform (VRW) is added to both strobe and data waveforms. This has the effect of reducing the maximum amplitude of voltage needed by the driver circuits, whilst leaving the resultant voltage appearing at a display element at the same value as if VRW were not used. With a reduced voltage requirement, driver circuits previously used for relatively low voltage menatic material type of displays can be used to switch smectic materials.
摘要:
The invention provides a surface, or electric field, stabilised ferroelectric liquid crystal (SSFLC) device with an improved contrast ratio between its two switched states. The device comprises a liquid crystal cell formed by a thin layer (7), typically 1 to 5 .mu.m thick, of a smectic liquid crystal material, eg a smectic c, held between two glass walls (2, 3) coated on their inner faces with electrodes (5, 6). Polarizers (8, 9) are arranged either side the walls (2, 3). The device is switched between two bistable states by application of unidirectional voltage pulses, with or without the simultaneous application of ac bias voltages. To obtain optimum contrast ratio CR, the optical axis of the polarisers are rotated away from a crossed, or othogonal position. eg by +/-20.degree., and the cell rotated between the polarisers (8, 9); the precise optimum rotation depends upon material, and ac bias voltage.