Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Amorphous semiconductor material
Reexamination Certificate
2001-01-17
2002-07-09
Wojciechowicz, Edward (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Amorphous semiconductor material
C257S013000, C257S079000, C257S423000
Reexamination Certificate
active
06417521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driver circuit of a semiconductor device and a semiconductor device using the driver circuit. Particularly, the invention relates to a driver circuit of a semiconductor display device for displaying a picture on a pixel portion by driving TFTs arranged in a matrix form. Further, the invention relates to a semiconductor display device using the driver circuit, particularly to a liquid crystal display device and an EL display device which is also called a light emitting device or a light emitting diode or an OLED (Organic Light Emission Diode). The EL (electroluminescent) devices referred to in this specification include triplet-based light emission devices and-or singlet-based light emission devices, for example.
2. Description of the Related Art
Recently, a technique for fabricating a semiconductor device in which a semiconductor thin film is formed on an inexpensive glass substrate, for example, a thin film transistor (TFT), has been rapidly developing.
Among thin film transistors, especially a polycrystalline silicon thin film (poly-Si TFT) can operate at high speed as compared with an amorphous thin film transistor. On this account, different from the case where the amorphous thin film transistor is used, in a semiconductor device using the polycrystalline silicon thin film transistor, a driver circuit can be directly formed on the same substrate as a pixel portion. Note that, in the present specification, an insulating substrate having a surface on which a semiconductor element is formed is called an active matrix substrate.
At present, the mainstream is a system (dot sequential analog system) in which as a video signal itself to be inputted to a driver circuit, an analog signal formed by an IC externally attached to a panel is written in a pixel as it is.
However, as an interface is digitized after this, it is presumed that a system (digital system) in which a video signal of a digital form, which is not decoded into an analog value, is directly taken into a driver circuit on a substrate, and the video signal of the digital form is converted into a video signal of an analog form by the driver circuit, will be more earnestly demanded.
FIG. 24
is a schematic view showing an example of an active matrix liquid crystal display device driven by a dot sequential analog system.
A source side driver circuit
1301
and a gate side driver circuit
1302
are parts of a driver circuit. In a pixel portion
1308
, source signal lines
1303
connected to the source side driver circuit
1301
intersect with gate signal lines
1304
connected to the gate side driver circuit
1302
. A pixel thin film transistor (pixel TFT)
1305
, a liquid crystal cell
1306
in which a liquid crystal is sandwiched between a counter electrode and a pixel electrode, and a storage capacitor
1307
are provided in a region including the source signal line
1303
and the gate signal line
1304
.
An analog video signal (analog signal containing image information) inputted to the source signal line
1303
is selected by the pixel TFT
1305
and is written in a predetermined pixel electrode.
The analog video signal sampled by a timing signal outputted from the source side driver circuit
1301
is supplied to the source signal line
1303
.
The pixel TFT
1305
is operated by a selection signal inputted from the gate side driver circuit
1302
through the gate signal line
1304
.
FIG. 25
is a schematic view showing a structure of an active matrix liquid crystal display device of a digital driver system. In this case, an active matrix liquid crystal display device of a 4-bit digital driver system is exemplified. The active matrix liquid crystal display device of the digital driver system includes, as shown in
FIG. 25
, a source side driver circuit
1412
, a gate side driver circuit
1409
, and a pixel portion
1413
.
The source side driver circuit
1412
includes a shift register
1401
, latches 1 (LAT 1)
1403
, latches 2 (LAT 2)
1404
, and D/A converter circuits
1406
. Address lines
1402
(
a-d
) of digital video signals (digital signals including image information) inputted from the outside are connected to the latches 1 (LAT 1)
1403
. A latch pulse line
1405
is connected to the latches 2 (LAT 2)
1404
. A gray-scale voltage line
1407
is connected to the D/A converter circuits
1406
. Each of the latches 1
1403
and the latches 2
1404
(LAT 1 and LAT 2) represents four latches in one bundle for convenience.
Source signal lines (also called data lines)
1408
connected to the D/A converter circuits
1406
of the source side driver circuit
1412
and gate signal lines (also called scanning lines)
1410
connected to the gate side driver circuit
1409
are provided in the pixel portion
1413
.
In the pixel portion
1413
, a pixel TFT
1411
and a liquid crystal cell
1414
are provided at a portion where the source signal line
1408
intersects with the gate signal line
1410
.
By the timing signal from the shift register
1401
, digital video signals supplied to the address lines
1402
(
a-d
) are sequentially written in all the latches 1
1403
. Note that, in this specification, all the latches 1
1403
are generally named a LAT 1 group.
A period in which writing of digital video signals into the LAT 1 group is once completed is called one line period. That is, one line period is a period from a point of time when writing of the digital video signal into the leftmost LAT 1 starts to a point of time when writing of the digital video signal into the rightmost LAT 1 is completed. Note that a combination of the period when writing of the digital video signals into the LAT 1 group is once completed and a horizontal retrace line period may be made one line period.
After the writing of the digital video signals into the LAT 1 group is completed, the digital video signals written in the LAT 1 group are transmitted and written into all the latches 2
1404
all at once by a latch signal inputted to the latch pulse line
1405
. Note that, in the present specification, all the latches 2 are generically named a LAT 2 group.
After the digital video signals are transmitted to the LAT 2 group, a second line period starts. Thus, by a timing signal from the shift register
1401
, writing of digital video signals supplied to the address lines
1402
(
a-d
) is sequentially performed again to the LAT 1 group.
At the same time as the start of this second one line period, the digital video signals written in the LAT 2 group are inputted to the D/A converter circuits
1406
all at once. The inputted digital video signals are converted into analog signals (analog gray-scale voltage signals) having voltages corresponding to image information of the digital video signals by the D/A converter circuits
1406
, and are supplied to the source signal lines
1408
.
The analog gray-scale voltage signals are supplied to the corresponding source signal lines
1408
during the one line period. Switching of the corresponding pixel TFT
1411
is performed by a selection signal outputted from the gate side driver circuit
1409
, and a liquid crystal molecule is driven by the analog gray-scale voltage signal from the source signal line
1408
.
The foregoing operation is repeated a predetermined number of times, the number being equal to the number of the gate signal lines, so that one screen (one frame) is formed. In general, in the active matrix liquid crystal display device, rewriting of images of 60 frames is performed in one second.
As described above, in the dot sequential analog system, a gray-scale display corresponding to a voltage of the analog video signal made of one analog gray-scale signal is effected. On the other hand, in the case of the digital driver system, in order to effect a display of, for example, 16 gray-scales, it is necessary to process a 4-bit digital video signal in the driver circuit. To this end, in the digital driver system, compared with the dot sequential analog system in which one analog signal is processed, it becomes ne
Fish & Richardson PC
Semiconductor Energy Laboratory Co,. Ltd.
Wojciechowicz Edward
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