HELICOS: Hand held reflective colour display

• Research unit: EU RFP
• Project number: 98.0033

Key words (English)

Polarizer-free reflective colour LCD; low-power high-voltage LCD driver

Alternative project number (English)

EU project number: 28131

Research programs (English)

EU-programme: 4. Frame Research Programme - 1.3 Telematic systems

Short description (English)

See abstract

Partners and International Organizations (English)

CRL (UK), Koordinator; ALCATEL (F); IMEC (B); TECDIS (I); Thomson-LCD (F); Universität Stuttgart (D)

Abstract (English)

The objective of the present project is the development of reflective multicolour liquid crystal displays (LCDs) for portable intelligent systems in which the available energy is limited. As the legibility of reflective display systems is dependent on ambient light conditions a major problem is the achievable reflectance. To address this problem, only liquid crystal (LC) effects not using polarisers are considered. Different LC effects have been evaluated and technology demonstrators have been built. The potential for high brightness compared to other technologies has been proven. Two LC technologies have been selected to build the final project display demonstrators. The selected effects are:1. Dye-doped LC with colour filters for active matrix drive2. Cholesteric LC (CLC) working in the 'Bragg reflection' mode without colour filters for passive matrix drive.Standard measurement procedures for the evaluation of the electro-optic performance of the reflective display demonstrators have been defined and implemented. Comparative measurements with commercially available reflective colour displays, which are all one-polariser devices, have been made as some kind of benchmarking of the state of the art.During the evaluation of the selected LC effects it has become clear that light 'shaping' films, e. g. front diffusing films or shaped reflectors, should be used to optimise the electro-optic performance of the displays and corresponding work has been carried out with promising results.CLCs have memory, which results in an infinite multiplexing ratio and extremely low power consumption if the refresh rate for the images is low (virtually zero for still images). However, special driving schemes and high switching voltages (about 70V) are necessary to take best advantage of the properties of CLCs. Therefore the development of a high-voltage low-power (HV-LP) driver in a high-voltage CMOS technology is included in this project. Patent applications have been filed for a new level shifter circuitry with extremely low power consumption and an 8-bit programmable HV generation block on chip. All functional blocks of the HV-LP driver have been designed and integrated separately. Then, two complete drivers have been designed and the first one has still been manufactured within the time frame of the project. ASULAB S.A., a company of Swatch Group and the Swiss partner in this project, is involved in the development of the passive drive LCD based on CLCs, the HV-LP LCD driver and the realisation of a passive LCD module which is to be commercialised by its sister company EM Microelectronics S.A.. These modules will be introduced in Swatch Group products but they will also be available as custom designed products for third parties.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0033