EP0580226A1

EP0580226A1 - Pilot system for a display panel utilizing ferroelectric crystals that provides the use of a pilot signal having a cancellation impulse

Info

Publication number: EP0580226A1
Application number: EP93202069A
Authority: EP
Inventors: Fabio Zuliani
Original assignee: SELECO SpA
Current assignee: SELECO SpA
Priority date: 1992-07-22
Filing date: 1993-07-16
Publication date: 1994-01-26
Also published as: ITTO920626A0; ITTO920626A1; IT1257391B

Abstract

The present invention refers to a pilot system for a display panel utilizing ferroelectric crystals; the main characteristic of the invention consists in that it provides the use of a pilot signal that has a cancellation impulse that precedes the writing impulses.

Description

The present invention refers to a pilot system for a display panel utilizing ferroelectric crystals.
Displays based on ferroelectric liquid crystals (SSFLC) have interesting characteristics, such as high resolution and memory (they are in fact bistable type elements).
The piloting of such kinds of display does however have some problems; it is in fact necessary to consider that ferroelectric crystals represent a particular state of liquid crystals, obtained from particular processing; the characteristics of the relative pilot system must be strongly correlated to the structure of the actual crystals; the form of the signals must be of the complex type and furthermore the actual characteristics vary generally with the variations of the temperature and of the form of the signals.
In particular the addressing diagram influences the characteristics of flicker, cross talk, motion performance, working procedure field.
Various diagrams of pilot signals are known (confront. T. Harada et al, SID Symposium Digest, Playa del Rey, May 1985, page. 131; C. Bowry et al, Eurodisplay 87, page. 152; P. Maltese et al, IEEE, Piscataway, oct. 88, page. 98).
The aim of the present invention is that of indicating a pilot system for a display panel utilizing ferroelectric crystals that has ameliorative characteristics, in particular as far as regards flicker, applied to images in movement and working field.
For achieving such aims the present invention has as its subject a pilot system for a display panel utilizing ferroelectric crystals, characterised in that it provides the use of a pilot signal that has a cancellation impulse that precedes the writing impulses.
Further aims and advantages of the present invention will result in being clear from the detailed description that follows and from the annexed drawings, supplied purely as an explanatory and non-limiting example, wherein:
The figure represents the diagram of the signal utilized for piloting a display panel according to the system subject of the present invention.
The diagram shown constitutes the path of the line signal (Vrow), that serves to activate a line of the display.
In the figure a first impulse (1) is seen that is a cancellation impulse (blanking) that has the aim of cancelling the information memorized by the crystals; said impulse is followed by a second equal impulse (2), of reversed polarity, of a distance of 5 time units (T), and by a third impulse (3), equal to impulse 1.
The impulses 2 and 3 immediately follow one after the other and are those which allow the writing of the new information on the display; T is in fact the writing time (write time), during which the voltage applied to the columns is received by the line in question.
The diagram represented in the figure without corrective actions would present two drawbacks:

a somewhat long duration (8 time units);
a value not null of the continuous component (two negative impulses and one positive).

For resolving the first drawback the scansion of the display takes place in a progressive manner (one line after another) with a displacement in time of two base units (2T); for resolving the second, the diagram is alternated (reversed polarity) every field in such a way to ensure a continuous component null to the ferroelectric material.
The pilot system according to the invention has demonstrated ameliorative characteristics as far as regards contrast, speed, flicker, cross-talk, working field, both in voltage and in frequency.
Hereinbelow some exemplified measures are reported (in lux), executed at a temperature of 23°C, 1000 lux of light source and 250 lux environment; writing time 70 microseconds; line tension (Vrow) equal to 28 V and column voltage (Vcol) equal to 9 V.

black white ratio

20 95 4,75

30 115 3,80

35 110 3,10
The characteristics of the pilot system subject of the invention result in being clear from the description of the example.
From the present description the advantages of the pilot system subject of the present invention are also clear.
It is clear that numerous variations are possible by the skilled-man, to the pilot system described by way of example, without departing from the novelty principles inherent in the invention.
For example there is the possibility of utilising the same principle diagram reversing the polarity of impulses 2 and 3 (impulse 2 negative and impulse 3 positive) with results being even better, even if with a loss of speed.

Claims

Pilot system for a display panel utilizing ferroelectric crystals, characterised in that it provides the use of a pilot signal having a cancellation impulse (1) that precedes the writing impulses (2,3).
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 1, characterised in that it provides the use of a pilot signal having a cancellation impulse (1) of determined duration (T) that precedes two writing impulses (2,3), of alternate polarity respect each other, and of the same duration as the cancellation impulse.
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 2, characterised in that the first writing impulse (2) has inverted polarity if compared to the cancellation impulse (1) and that the second writing impulse (3) has the same polarity as the cancellation impulse.
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 2, characterised in that the first writing impulse (2) has the same polarity as the cancellation impulse (1) and that the second writing impulse (3) has inverted polarity if compared to the cancellation impulse.
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 1, characterised in that said cancellation impulse precedes the first writing impulse (2) by 5 time units (T).
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 2, characterised in that the first writing impulse (2) immediately precedes the second writing impulse (3).
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 2, characterised in that said signal is deplaced in the time by two time units (2T) one line after the other is alternated (inverted polarity ) every field in such a way to ensure a continuous component null to the FLC material.
Pilot system for a display panel utilizing ferroelectric crystals, according to claim 2, characterised in that said signal polarity is inverted with every field in a such a way to ensure a continuous component substantially null.
Circuit for generating a pilot signal for a display panel utilizing ferroelectric crystals as resulting from the present description and annexed drawings.
Pilot system for a display panel utilizing ferroelectric crystals, as resulting from the present description and annexed drawings.