Variable current controller

Details Variable current controller Variable current controller

2000-12-08

2003-10-21

Saras, Steven (Department: 2675)

Computer graphics processing and selective visual display system

Display driving control circuitry

Display power source

C345S212000, C345S060000, C345S214000

Reexamination Certificate

active

06636209

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a display apparatus arranged to limit an electric current therein, and more particularly to a display apparatus, such as a CRT, a plasma display, an LED display and a field emission display, having a characteristic that power consumption varies when the brightness of a displayed image varies.
Self-emission type display apparatuses including CRT, a plasma display, an LED display and a field emission display, generally encounter vary in power consumption therein when the brightness of a displayed image varies.
The reason for this lies in that the quantity of electric currents which flow in the display portion is enlarged because light beams must be emitted more intensely and the number of emission times must be enlarged when a bright image is displayed. When a dark image is displayed, the quantity of electric currents which flow in the display portion is reduced because light beams must be weakened and the number of emission times must be decreased.
Under circumstances where saving of the energy resources is required from a global viewpoint, e.g. display apparatuses are required to have large-size screens and display apparatuses as used in vehicles and on portable telephones, power saving has been required for the display apparatus. Power saving realizes advantages for users and attains effects to be obtained in that loads which must be borne by the display portion and the power supply circuit of the display apparatus can be reduced, the size of circuit can be reduced and low-cost elements can be employed. In addition, the lifetime of the display apparatus can be extended.
Therefore, a method has recently been employed which uses a characteristic which is apparent for a self-emission type display apparatus and with which power consumption varies when the brightness of a displayed image varies in order to save power.
Referring to the drawings, an example of the current limiting circuit will now be described in such a manner that a conventional current limiting circuit employed in a plasma display is taken as an example.
FIG. 15
is a block diagram showing an essential portion of the display apparatus having the conventional current limiting circuit. Referring to
FIG. 15
, reference numeral
1
represents an A/D conversion means for video signals,
2
represents a video-signal processing means,
3
represents a storage means,
4
represents a display sequence control means,
5
represents a panel of the plasma display,
11
represents a means
11
for generating the number of pulses to be retained,
12
and
31
represent multiplying means,
32
represents a smoothing means and
33
represents a pulse controlled-variable calculating means.
The operation will now be described. The operation which is performed until an image is displayed will now be described in accordance with the flow of a video signal. The A/D conversion means
1
A/D-converts an analog video signal
101
which is supplied to the plasma display to output digital video data
102
. The video signal is treated as digital data in a portion following the A/D conversion means
1
. The video-signal processing means
2
subjects digital video data
102
output from the A/D conversion means
1
to brightness, contrast, color temperature correction and gamma conversion processes to output video signal data
103
subjected to the video signal process. The storage means
3
has two storage means, which are a first storage means
36
and a second storage means
37
, as shown in FIG.
16
. Each of the storage means is a field memory or a frame memory. When the display method of the panel is interlace display, the storage means is able to store video signal for two fields. When the display method is progressive display, the storage means is able to store video signal for two frames. Selectors
38
and
39
disposed in front and behind the storage means
36
and
37
are exclusively and independently operated. When the first selector
38
adjacent to the input portion selects the first storage means
36
, the second selector
39
adjacent to the output portion selects the second storage means
37
. When the first selector
38
adjacent to the input portion selects the second storage means
37
, the second selector
39
adjacent to the output portion selects the first storage means
36
. If the first selector
38
adjacent to the input portion selects the first storage means
36
, the first storage means
36
is being operated in a write mode. Thus, video signal data
103
supplied to the storage means is written on the first storage means
36
. In the foregoing period, the second storage means
37
is operated in the reading mode so that sub-field data
104
having a predetermined number of bits is read from the second storage means
37
. When the storage means
3
is interposed, video signal data
103
can be converted into a plurality of sub-field data items
104
which are divided in terms of time. Therefore, the storage means
3
is an important element for the plasma display which displays a gray-scale image by performing pulse-width modulation also when the interlace display is performed. The display sequence control means
4
outputs, to the panel
5
, sub-field data
104
of the image signal read from the storage means
3
as write data
105
for selecting cells in the panel
5
from which light is emitted. The panel
5
operates writing electrodes and displays the image in accordance with write data
105
.
The operation will now be described which is performed until the number of pulses to be retained for generating retaining discharge to cause the panel to emit light is determined, the description being performed along the flows of data of the number of pulses to be retained. A means
11
for generating the number of pulses to be retained generates and outputs data
111
of the number of pulses to be retained which corresponds to sub-fields. A multiplying means
12
multiplies data
111
of the number of pulses to be retained output from the means
11
for generating the number of pulses to be retained and a controlled variable
124
of the number of pulses (to be described later) for limiting the electric current to output data
112
of the number of pulses to be retained after the electric current is limited. The display sequence control means
4
generates pulse-shape data
113
for causing the panel to emit light by the number instructed with data
112
of the number of pulses to be retained after the electric current is limited. The display sequence control means
4
writes a display position on the panel with write data
105
corresponding to the sub-field, and then outputs, to the panel
5
, pulse-shape data
113
for causing the panel to emit light. The panel
5
applies pulse-shape waveform to an electrode after data is written on the panel so that only cells written with write data
105
emit light in accordance with pulse-shape data
113
so that an image is displayed.
The operation for limiting the electric current will now be described. The multiplying means
31
multiplies sub-field data
104
of the video signal output from the storage means
3
and data
112
of the number of pulses for retaining light emission which is output to the panel to perform an equivalent calculation of the quantity of light to be emitted from the panel in one sub-field period. Then, the multiplying means
31
outputs pseudo quantity
131
of light to be emitted which is obtained by the equivalent calculation. Sub-field data
104
of the video signal corresponds to the number of cells which emit light, while data
112
of the number of pulses to be retained corresponds to the number of light emitting operations of each cell. The smoothing means
32
subjects the pseudo quantity
131
of-light to be emitted which varies in sub-field units to a smoothing process to output a smoothed quantity
132
of light to be emitted. The pulse controlled-variable calculating means
33
causes a deviation detection means
34
to obtain deviation
133
of the quantity
132
of light

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