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Browse Prior Art Database

Analog Gamma Compensation Circuit for Liquid Crystal Display

IP.com Disclosure Number: IPCOM000114291D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Kobayashi, Y: AUTHOR [+3]

Abstract

This invention disclosure describes an analog circuit that performs gamma compensation of video signals (analog R/G/B signals) for Liquid Crystal Displays (LCDs). After transforming the video signals, the circuit will supply them to analog LCD drivers.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 78% of the total text.

Analog Gamma Compensation Circuit for Liquid Crystal Display

      This invention disclosure describes an analog circuit that
performs gamma compensation of video signals (analog R/G/B signals)
for Liquid Crystal Displays (LCDs).  After transforming the video
signals, the circuit will supply them to analog LCD drivers.

      The circuit consists of multiple differential amplifiers, of
which input-to-output characteristics are adjusted appropriately as
described below.  Gamma compensation is realized by piling up the
characteristics of the differential amplifiers.

      Fig. 1 shows an example of the gamma compensation circuit that
consists of four differential amplifiers: A1, A2, A3, and A4.  Analog
video signals are supplied to Vin in Fig. 1, and the transformed
video signals are output from +Vout and -Vout.  The -Vout is the
inverse of the +Vout, and is used for the voltage inversion, which is
a mandatory requirement for LCDs.

      The input-to-output characteristics of the A1, A2, A3, and A4
differential amplifiers are illustrated at the bottom of Fig. 2.  The
input-to-output characteristic of the gamma compensation circuit,
which is a result of the pile of the characteristics of the four
differential amplifiers, is shown at the top of Fig. 2.

      There are five control points in the example circuit shown in
Fig. 1: four resisters of the four differential amplifiers and Vref
(voltage reference).  The resisters are used to control the slop...