Browse Prior Art Database

Analog Gamma Compensation Circuit

IP.com Disclosure Number: IPCOM000114589D
Original Publication Date: 1995-Jan-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Kobayashi, Y: AUTHOR [+2]

Abstract

This invention disclosure describes a gamma compensation circuit for Thin-Film Transistor/Liquid Crystal Displays (TFT/LCDs). It consists of four Inversion Amplifiers (IAs), each of which is made up of two transistors (i.e., 8 transistors in total).

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Analog Gamma Compensation Circuit

      This invention disclosure describes a gamma compensation
circuit for Thin-Film Transistor/Liquid Crystal Displays (TFT/LCDs).
It consists of four Inversion Amplifiers (IAs), each of which is made
up of two transistors (i.e., 8 transistors in total).

      Fig. 1 shows a circuit diagram of the invention, which contains
four IAs.  The input-to-output characteristic of each IA is
illustrated in Fig. 2-(1).  The combination of IAs 2 and 3 in Fig. 1
(i.e., double inversion) can be treated as a single non-inversion
amplifier.  Its input-to-output characteristic is shown in Fig. 2-(2)
and the characteristic around Vcent is sharp due to the double
inversion effect.  The output signal at Point 3 in Fig. 1 is fed back
to Point 2 through IA 4.

      The power supply voltage for IA 4 is set lower than those of
the other IAs, and the non-saturation region of IA 4 is narrower than
those of the others.  This non-saturation region is used as the
linear region of the gamma compensation.

      Waveforms at Points 1, 2, and 3 in Fig. 1 are shown in Figs.
3-(1), (2), and (3), respectively.  In Fig. 3-(3), the valid range of
the input voltage is Vlow through Vhigh.  Thus, Vlow has to be added,
as an offset voltage, to the input video signal at actual usage.  The
gamma compensation characteristic shown in Fig. 3-(3) is for
so-called normally-white LCDs.  For so-called normally-black LCDs,
video signals need to be inverted before...