GB2287350A - Display module - Google Patents

Abstract

A display module, for use with a pixellated display of the type comprising an array of liquid crystal shutters each disposed in front of a light source, comprising a circuit board 1 including an aperture 2 on either side of which a liquid crystal cell 3, 4 is attached. Each liquid crystal cell includes an array of opposed electrodes so as to define an array of shutters 5. The shutters 5 of each cell are aligned with each other. A driver circuit 8 for the cells is mounted on the circuit board and conductive tracks 9 are provided on each face of the board to connect the driver circuit to each cell 3, 4 in parallel. <IMAGE>

Description

DISPLAY MODULE This invention relates to a display module for use with a pixellated display of the type comprising an array of liquid crystal shutters each disposed in front of a light source. Selective actuation of the shutters can cause a message or character to be displayed.

Under certain circumstances a single liquid crystal cell, in the non light transmitting state, can be insufficient to adequately mask the light source. For this reason it has been proposed to use two cells one disposed in front of the other. Typically one may comprise a Heilmeyer cell and the other that of a Twisted Nematic type.

The liquid crystal cells are delicate and can be prone to failure and it is important that they can be easily replaced.

This invention provides a display module for use with a pixellated display of the type comprising an array of liquid crystal shutters each disposed in front of a light source, the module comprising a circuit board including an aperture, a liquid crystal cell being attached to each face of the board overlying the aperture, each liquid crystal cell including an array of opposed electrodes defining an array of shutters, shutters of each cell being aligned with each other, driver circuit for the cells being mounted on the circuit board, conductive tracks being provided on each face of the board to connect the driver circuit to each cell in parallel.

The circuit board provides mechanical support for each of the liquid crystal cells and furthermore ensures that electrical connection can be provided to each board in a straight forward way. An advantage of the invention is that by attaching a liquid crystal cell to each face of the board balances the forces that would arise due to the different coefficients of expansion of the cell and board materials.

An embodiment of the invention will now be described with reference to the accompanying drawing which is an exploded perspective view of a display module according to the invention.

A display module comprises a circuit board 1 of generally rectangular shape having a rectangular aperture 2 formed therein. A liquid crystal cell 3, 4 is attached to each face la, ib respectively, of the circuit board using adhesive 14 applied to the corners of the cells 3, 4 such that the cells 3,4 overlie the aperture 2. Each liquid crystal cell 3,4 includes an array of shutters or pixels 5 each defined where opposed electrodes, not shown, of transparent ITO overlap one another. Application of a control voltage to a selected shutter 5 can cause the cell locally to change between light transmitting and non transmitting states so that a light source (not shown) disposed behind the module can be selectively shuttered. Each module can conveniently be used to display a single alpha-numeric character. The electrodes on each cell are attached by a heat bonded ribbon cable 6, 7 to the circuit board 1. An integrated driver circuit 8 is attached to the circuit board and conductive tracks 9 provided on each face of the board convey the control signals from the driver integrated circuit 8 to the respective ribbon cable 6, 7. The board includes plated through holes 10, where the pins 8a on the integrated circuit pass through the board 1, for interconnecting the tracks 9 on each side of the board. A connector 11 is also provided on the board for applying the control signals from the host system to the integrated circuit 8. A further connector 12 is provided for daisy chaining the module to other such modules so that control signals can be applied simultaneously to each module.

Conveniently one of the cells 3 is of the Heilmeyer type and the other is of the Twisted Nematic type. Attaching a liquid crystal cell 3, 4 to each face of the circuit board 1 balances the forces that would arise due to the different coefficients of expansion of the cell and board materials. Balancing these forces reduces the likelihood of the board and cells becoming separated or distorted.

Claims (5)

1. A display module for use with a pixellated display of the type comprising an array of liquid crystal shutters each disposed in front of a light source, the module comprising a circuit board including an aperture, a liquid crystal cell being attached to each face of the board overlying the aperture, each liquid crystal cell including an array of opposed electrodes defining an array of shutters, shutters of each cell being aligned with each other, driver circuit for the cells being mounted on the circuit board, conductive tracks being provided on each face of the board to connect the driver circuit to each cell.

2. A display module according to claim 1 in which the circuit board includes plated through holes to interconnect the conductive tracks on each face of the board.

3. A display module according to any preceding claim in which the liquid crystal cells are connected to the conductive tracks by heat bondable ribbon cables.

4. A display module for a single alpha-numeric character displaying according to any preceding claim.

5. A display module substantially as described with reference to the accompanying drawings.