Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-04-14
2001-12-18
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C330S252000
Reexamination Certificate
active
06331846
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a downsized less-power-consuming differential amplifier which is insensitive to an incidental offset voltage caused by discrepancies in material and workmanship. The present invention also relates to an operational amplifier employing such a differential amplifier and a liquid crystal driving circuit incorporating such an operational amplifier.
BACKGROUND OF THE INVENTION
FIG. 37
is a block diagram of an example of a conventional TFT liquid crystal display representing liquid crystal displays of an active matrix method. Numeral
3801
denotes a TFT liquid crystal panel, numeral
3802
denotes a source driver IC having a plurality of source drivers, numeral
3803
denotes a gate driver IC having a plurality of gate drivers, numeral
3804
denotes a controller, and numeral
3805
denotes a liquid crystal driving power source (power source circuit).
The controller
3804
sends a vertical synchronizing signal to the gate driver IC
3803
, and a horizontal synchronizing signal to both the source driver IC
3802
and gate driver IC
3803
. Display data inputted from the outside are entered into the source driver IC
3802
through the controller
3804
in the form of a digital signal. The source driver IC
3802
latches the input display data in a time-sharing method. Then, the source driver IC
3802
converts the digital signal to an analog signal in sync with the horizontal synchronizing signal from the controller
3804
and outputs the analog voltage from a liquid crystal driving output terminal to be used for gradation display.
FIG. 38
shows an arrangement of the TFT liquid crystal panel. Numeral
3901
denotes a pixel electrode, numeral
3902
denotes a pixel capacitance, numeral
3903
denotes a TFT (switching element), numeral
3904
denotes a source signal line, numeral
3905
denotes a gate signal line, and numeral
3906
denotes a counter electrode.
The source signal line
3904
is supplied with a gradation display voltage from the source driver IC
3802
, which varies in response to brightness of a display pixel. The gate signal line
3905
is supplied with a scanning signal from the gate driver IC
3803
, whereby vertically aligned TFTs
3903
are successively turned ON. Through the TFT
3903
which stays ON, a voltage supplied to the source signal line
294
is applied to the pixel electrode
3901
connected to the drain of that particular TFT
3903
. The applied voltage is accumulated in the pixel capacitance
3902
between the TFT
3903
and counter electrode
3906
, in response to which light transmittance of the liquid crystal varies. Accordingly, display in accordance with the variance of the light transmittance is shown.
Examples of a liquid crystal driving waveform are shown in
FIGS. 39 and 40
. Numerals
4001
and
4101
represent driving waveforms of the source driver, numerals
4002
and
4102
represent driving waveforms of the source driver, and numerals
4003
and
4103
indicate potentials of the counter electrode, and numerals
4004
and
4104
represent voltage waveforms of the pixel electrode.
A voltage applied to the liquid crystal material is a potential difference between the pixel electrode
3901
and counter electrode
3906
, which is indicated as a shaded portion in the drawings. The liquid crystal panel has to be driven by an alternating voltage to ensure long-term reliability.
FIG. 39
shows a case where the TFT
3903
is turned ON by an output from the gate driver when an output voltage of the source driver is higher than a voltage of the counter electrode. Thus, a positive voltage with respect to the counter electrode
3906
is applied to the pixel electrode
3901
.
FIG. 41
shows an example of a polarity alignment on the liquid crystal panel
3801
to obtain an alternating driving voltage. This example is based on so-called dot-inverting driving, and positive polarities and negative polarities are aligned vertically and horizontally in an alternating sequence on one screen (frame), and each polarity is inverted per frame. According to this method, in the source driver IC
3802
, when odd-numbered output terminals output positive voltages, even-numbered output terminals output negative voltages. Conversely, when the odd-numbered output terminals output negative voltages, even-numbered output terminals output positive voltages.
FIG. 42
shows an example driving waveform of the source driver by dot-inverting driving. In the drawing, numeral
4301
represents an output voltage waveform of the odd-numbered output terminals, numeral
4302
represents an output voltage waveform of the even-numbered output terminal, and numeral
4303
represents a voltage of the counter electrode
3906
. As shown in the drawing, the odd-numbered output terminal and even-numbered terminal constantly output voltages of opposite polarities with respect to the counter electrode
3906
.
FIG. 43
shows a block diagram of an example arrangement of the source driver IC
3802
. The display data (R,G,B) inputted in the form of a digital signal is time-shared based on an operation of a shift register
4403
, stored into a sampling memory
4404
, and transferred collectively to a hold memory
4405
at the timing of a horizontal synchronizing signal. The shift register
4403
is designed to operate based on a start pulse and a clock (CK). The data in the hold memory
4405
are converted to an analog voltage by a digital-to-analog converter (DAC)
4407
through a level shifter
4406
, and outputted as a gray scale display driving voltage (liquid crystal driving voltage) from an output circuit
4408
through a liquid crystal driving output terminal.
FIGS.
44
(
a
) and
44
(
b
) show a block diagram and an operation of an example output circuit of a source driver IC which carries out dot-inverting driving in accordance with a prior art (first prior art). In these drawings, blocks denoted by numerals
4405
,
4407
and
4408
in
FIG. 43
are illustrated as 2-output terminal circuits.
In these drawings, numeral
4501
denotes a voltage follower which is an output circuit employing an operational amplifier to drive the odd-numbered output terminal, numeral
4502
denotes a voltage follower which is an output circuit employing an operational amplifier identical with the one used for the output circuit
4501
to drive the even-numbered output terminal, numerals
4503
,
4504
,
4505
, and
4506
denote output alternating switches which switch the polarity of the output voltage of a liquid crystal driving output, numeral
4507
denotes a digital-to-analog converter which converts a digital signal of a positive voltage to an analog signal, numeral
4508
denotes another digital-to-analog converter which converts a digital signal of a negative voltage to an analog signal, numerals
4509
and
4510
denote hold memories which withhold display data, numeral
4511
denotes an odd-numbered output terminal, and numeral
4512
denotes an even-numbered output terminal. Numeral
4513
in the operational amplifier
4501
and numeral
4514
in the operational amplifier
4502
denote operational amplifiers with N-channel MOS inputs, and numeral
4515
in the operational amplifier
4501
and numeral
4516
in the operational amplifier
4502
denote operational amplifiers with P-channel MOS inputs.
The following will explain a method of alternating the liquid crystal driving waveforms by the above-arranged circuits.
When the output alternating switches
4503
through
4506
are in the state shown in FIG.
44
(
a
), the display data for the odd-numbered output terminal
4511
stored in the hold memory
4509
are inputted to the positive digital-to-analog converter
4507
. The resulting analog voltage is outputted to the liquid crystal panel
3801
from the odd-numbered output terminal
4511
through the voltage follower
4501
. The output voltage thus obtained is used as a positive liquid crystal driving voltage.
In contrast, when the output alternating switches
4503
through
4506
are in the state shown in FIG.
44
(
b
), the display data f
Hjerpe Richard
Laneau Ronald
Sharp Kabushiki Kaisha
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