Browse Prior Art Database

Digital-To-Analog Converter for LCD Polarization

IP.com Disclosure Number: IPCOM000038678D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Cukier, M: AUTHOR

Abstract

A drawback of the liquid crystal device (LCD) displays is the small viewing angle. To be read by the operator, the LCD screen must be properly oriented. The viewing angle can be changed by adjusting a dedicated input voltage. With a system such as a modem provided with a keyboard and a non- volatile memory, the operator can enter into memory the information like a word representing the desired polarization voltage. Thus, the operator can adjust this voltage for maximum visual confort. The object of this invention is to provide a digital-to-analog converter to convert the word entered by the operator at the keyboard into a polarization voltage. Digital-To-Analog Converter As shown in Fig. 1, the digital-to-analog converter consists of a Polynomial Counter, a Combinatorial decoder and an RC integrator.

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Digital-To-Analog Converter for LCD Polarization

A drawback of the liquid crystal device (LCD) displays is the small viewing angle. To be read by the operator, the LCD screen must be properly oriented. The viewing angle can be changed by adjusting a dedicated input voltage. With a system such as a modem provided with a keyboard and a non- volatile memory, the operator can enter into memory the information like a word representing the desired polarization voltage. Thus, the operator can adjust this voltage for maximum visual confort. The object of this invention is to provide a digital-to- analog converter to convert the word entered by the operator at the keyboard into a polarization voltage. Digital-To-Analog Converter As shown in Fig. 1, the digital-to-analog converter consists of a Polynomial Counter, a Combinatorial decoder and an RC integrator. The Combinatorial Decoder receives as inputs the bits R0-R3 of the digital number to be converted, and the outputs Q0-Q3 of the polynomial counter. It produces, at its output, a sequence of constant pulses the number of which is equal to the digital number to be converted. Then, constant pulses of the output sequence are averaged and smoothed in the RC integrator having a time constant large compared with the pulse sequence time, such that the analog voltage across the capacitor is a measure of the pulse rate and therefore proportional to the input digital number. Polynomial Counter This counter, shown on Fig. 2, is built out of a 4-bit shift register, the input of which receives the output of the Exclusive-OR circuit XOR 2. One of the two...