Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-18
2002-03-26
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S078000, C345S092000, C315S291000
Reexamination Certificate
active
06362798
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the technical field of transistor circuits including a plurality of transistors such as thin-film transistors (mentioned as TFT hereafter), field effect transistors and bipolar transistors, and particularly relates to the technical field of transistor circuits including driving transistors for controlling driving current, by controlling conductance between the source and the drain in response to voltage supplied to the gate, that is supplied to a driven element such as a current-controlled (current-driven) element through the source and the drain.
2. Description of Related Art
Generally, the voltage/current characteristics and thresholds of transistors tend to vary, depending on various conditions such as the quality and thickness of semiconductor films, impurity concentration and diffusion areas, the quality, thickness and the like of gate insulating films, operating temperature, and the like. In the case of bipolar transistors consisting of crystal silicon, the variance of thresholds is relatively small, but in the case of TFTs, the variance is usually large. Particularly, in the case of TFTs formed in a wide range in plurality on a TFT array substrate in a display panel such as a liquid crystal panel, an EL panel, and the like, the variance in voltage/current characteristics and thresholds often becomes extremely large. For instance, when such TFTs are manufactured so as to set the threshold at about 2V (+2V in the case of N channel, and −2V in the case of P channel), the variance is sometimes about several ±V.
In the case of a voltage-controlled (voltage-driven) type transistor for controlling the voltage of picture elements made of liquid crystals or the like, such as a so-called TFT liquid crystal panel, the variance in voltage/current characteristics and thresholds of driving TFTs that are applied to each picture element is not likely to be a problem. In other words, in this case, even if there is a slight variance in the voltage/current characteristics and thresholds of TFTs, contrast and brightness of each picture element can be controlled at high precision by increasing the precision of the voltage supplied to each picture element from the outside through the TFTs only if there is enough switching time. Therefore, even in the case of a TFT liquid crystal panel or the like for display wherein contrast and brightness at each picture element are regarded as important, high grade picture images or the like can be displayed by TFTs with a relatively large variance of voltage/current characteristics and thresholds.
On the other hand, display panels have been recently developed that include current-controlled light-emitting elements, such as a self light-emitting organic ELs to change the brightness at picture elements in response to current supply. These display panels have received attention as display panels that can display picture images without back light and reflected light, that consume less power, being less dependent on the angle of view, and are sometimes flexible. Even in this EL panel, a driving TFT is used at each picture element for driving an active matrix. For instance, it is constructed so as to control (change) the driving current supplied to an EL element from power source wiring connected to a source in response to the voltage of data signals applied to a gate, by connecting the drain of a driving TFT to the EL element through a hole-injecting electrode. Using a driving TFT as mentioned above, driving current flowing to an EL element can be controlled by controlling conductance between a source and a drain in response to the voltage change of input signals, so that brightness at each picture element can be changed for picture image display and the like.
However, particularly in the case of the current-controlled element such as the EL panel mentioned above, the variance of voltage/current characteristics and thresholds tends to be a problem in the driving TFT at each picture element. In other words, in this case, even if the voltage precision of data signals supplied to the driving TFTs from the outside is enhanced to some extent, the variance in voltage/current characteristics and thresholds in the driving TFTs appears directly as the variance of the driving current supplied to data signals, thus reducing the precision of the driving current. As a result, the brightness at each picture element is likely to vary in accordance with the variance in thresholds of the driving TFTs. Moreover, especially with current manufacturing techniques of low temperature polysilicon TFTs, voltage/current characteristics and thresholds vary considerably. Thus, this problem is, in practicality, extremely serious.
SUMMARY OF THE INVENTION
If each TFT is manufactured so as to reduce the variance in voltage/current characteristics and thresholds in consideration of this problem, the yield will decline and, particularly in the case of an apparatus with a display panel having a plurality of TFTs, the yield will decrease a great extent, and thus opposing a general goal of lower costs. Alternatively, it is almost impossible to manufacture TFTs that can lower such a variance. Moreover, even if a circuit for compensating the variance of voltage/current characteristics and thresholds at each TFT is installed separately, the apparatus will be complex and large, and moreover, the consumption of electric power will increase. Particularly, in the case of a display panel wherein a plurality of TFTs are arranged at high density, the yield will decline again or it will be difficult to satisfy current demands such as lower power consumption, and miniaturization and lightening of an apparatus.
This invention is carried out in consideration of the above-noted problems, and aims to provide transistor circuits for controlling conductance in driving transistors in response to the voltage of input signals, the conductance of which can be controlled by relatively small input signals and that can compensate for the variance in voltage/current characteristics and thresholds of driving transistors with somewhat smaller power consumption by using a relatively small number of transistors, and a display panel and an electronic apparatus using the same.
In this invention, the following transistor circuits according to the first to tenth aspects are provided.
First, according to a first aspect of the invention a transistor circuit is characterized in that it includes a driving transistor having a first gate, a first source and a first drain, wherein conductance between the first source and first drain is controlled in response to the voltage of input signals supplied to the first gate, and a compensating transistor having a second gate, a second source and a second drain, wherein the second gate is connected to one of the second source and second drain, and wherein the compensating transistor is connected to the first gate in an orientation so as to supply the input signals to the first gate through the second source and second drain, and to allow the first gate to move electric charge into a direction to lower the conductance.
According to the above-noted transistor circuit of the first aspect of the invention, one of the second source and second drain of the compensating transistor is connected to the first gate of the driving transistor, and input signals are supplied to the first gate of the driving transistor through this second source and second drain. Then, at the driving transistor, the conductance between the first source and first drain is controlled in response to the voltage of input signals supplied to the first gate. Herein, the compensating transistor has the second gate connected to the second drain, and is connected to the first gate in an orientation to allow the first gate to move electric charge into a direction to lower the conductance between the first source and first drain. In other words, the compensating transistor has diode characteristics and when the driving transistor is, for e
Kimura Mutsumi
Matsueda Yojiro
Ozawa Tokuroh
Quinn Michael
Oliff & Berridg,e PLC
Piziali Jeff
Seiko Epson Corporation
Shalwala Bipin
LandOfFree
Transistor circuit, display panel and electronic apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transistor circuit, display panel and electronic apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transistor circuit, display panel and electronic apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2831657