Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-04
2003-08-05
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000
Reexamination Certificate
active
06603456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a signal amplifier circuit, a load drive circuit and a liquid crystal display device using them.
2. Description of the Related Art
A liquid display device, in general, is made up of a pixel array portion with a matrix arrangement of signal lines and scanning lines, and drive circuits for driving the signal lines and the scanning lines. Conventionally, since the pixel array portion and the drive circuits were formed on separate substrates, it was difficult to reduce the cost of the liquid display device, and it was also difficult to increase the ratio of the real screen size relative to the outer dimension of the liquid crystal display device.
Recently, however, since the manufacturing technology for making TFT (thin film transistor) on a glass substrate by using polysilicon as its material has been progressed, it has been made possible to make the pixel array portion and the drive circuits on a common glass substrate by using the technology.
Apart from this, especially as a technological tendency of recent liquid crystal display devices integral with a drive circuit, it is getting more and more active to develop a liquid crystal device enabling direct input of a digital signal to the drive circuits on a glass substrate by configuring the drive circuits in the liquid crystal device to have the function of converting the digital signal to an analog video signal.
In a liquid display device particularly of a direct viewing type, however, digital input signals introduced from outside are supplied to the signal line drive circuit through a wiring on glass having a large resistance load and capacitance load. Therefore, in order to ensure direct supply of digital input signals from outside to the drive circuit on the glass substrate, it was necessary to supply digital input signal by using a signal supply circuit with a large drive power. As a result, it was necessary to additionally use another signal drive circuit for the digital input signals of the large drive power.
Moreover, since making uniform and good-property polysilicon TFT on a glass substrate is still difficult, the drive circuit on the glass substrate cannot be driven directly with digital input signals having an amplitude used in an external circuit unchanged, and it was necessary to additionally use a signal amplifier circuit for amplifying the amplitude of the digital input signals.
That is, it was necessary for the drive circuit on the glass substrate to include a signal amplifier circuit. And, it was necessary to introduce digital input signal into the signal amplifier circuit, amplify their amplitude, then output them as digital output signals, and use the digital output signals to activate the drive circuit.
However, because it was difficult to form polysilicon TFT with a uniform property on the glass substrate, it was also difficult to unify the property of the amplitude amplifying logic circuit provided in the signal amplifier circuit. Therefore, threshold voltage of the amplitude amplifying logic circuit may vary among blocks or products.
In case where, for example, a digital input signal has an amplitude from 4V to 6V, and it is to be amplified into a signal having an amplitude from 0V to 10V by the signal amplifier circuit, threshold voltage of the amplitude amplifying logic circuit in the signal amplifier circuit should be set to 5 V. However, in some cases, polysilicon TFT forming the amplitude amplifying logic circuit varied in property and caused the threshold voltage to become 4.5 V or 5.5 V. In this case, a difference was produced between the timing when the digital input signal changes from 4V to 6V and the timing when the digital output signal changes from 0V to 10V.
In addition, when the threshold voltage of the amplitude amplifying logic circuit came largely offset to become 6.5 V, the digital output signal did not change to 10 V even upon entry of the digital signal having the amplitude from 4V to 6V. So, defective products were produced.
Furthermore, making polysilicon TFT having a uniform property on a glass substrate is still difficult, and it results in variation in the threshold voltage and mobility. Therefore, even if the pixel array portion and the drive circuit are formed on a common substrate, there is still the possibility that variation in property of TFT causes a deterioration of the display quality such as inconsistent in luminance, and power consumption increases as well.
SUMMARY OF THE INVENTION
The invention has been made taking these points into consideration, and its object lies in providing a signal amplifier circuit capable of operating normally even under variation in threshold voltage of an amplitude amplifying logic circuit in a signal amplifier circuit. That is, it is the object of the invention to provide a signal amplifier circuit normally operable even when the property of polysilicon TFT forming the amplitude amplifying logic circuit is not always uniform.
Another object of the invention is to provide a load drive circuit preventing that a voltage supplied to a driven load fluctuates due to an influence from unevenness of the transistor property.
A feature of the signal amplifier circuit according to the invention lies in comprising:
an amplitude amplifying logic circuit for amplifying a signal having the first amplitude to a signal having the second amplitude larger than the first amplitude, and outputting it as the digital output signal;
a differential voltage hold circuit having one end connected to the amplitude amplifying logic circuit for temporarily holding a differential voltage between a reference voltage of a voltage value for switching the digital input signal between HIGH and LOW and a voltage substantially equal to the threshold voltage for switching the logic of the amplitude amplifying logic circuit between HIGH and LOW;
a threshold voltage setting circuit for setting one end of the differential voltage hold circuit in a voltage substantially equal to the threshold voltage of the amplitude amplifying logic circuit when setting in the differential voltage hold circuit the differential voltage which the differential voltage hold circuit should hold;
a reference voltage setting circuit for setting the other end of the differential voltage hold circuit in a reference voltage for switching the logic of the digital input signal between HIGH and LOW when setting in the differential voltage hold circuit the differential voltage which the differential voltage hold circuit should hold; and
a digital signal input circuit for inputting the digital input signal to the other end of the differential voltage hold circuit after the differential voltage hold circuit holds the differential voltage.
A feature of the liquid crystal display device according to the invention lies in comprising:
a pixel array portion formed on a transparent substrate, having signal lines and scanning lines aligned in longitudinal and transverse directions and having pixel electrodes near respective nodes of those lines; and
a drive circuit formed on the transparent substrate to drive the signal lines and/or the scanning lines, and functioning to convert a digital video signal into an analog video signal,
the drive circuit including a plurality of signal amplitude amplifier circuits supplied with a digital input signal having a first amplitude and amplifying the amplitude of the digital input signal to output it as a digital output signal having a second amplitude larger than the first amplitude, the signal amplitude amplifier circuit having:
an amplitude amplifying logic circuit for amplifying a signal having the first amplitude to a signal having the second amplitude larger than the first amplitude, and outputting it as the digital output signal;
a differential voltage hold circuit having one end connected to the amplitude amplifying logic circuit for temporarily holding a differential voltage between a reference voltage of a voltage value for switching the digital input signal between HIGH and LOW and a voltage sub
Aoki Yoshiro
Karue Masao
Hjerpe Richard
Kabushiki Kaisha Toshiba
Nguyen Kevin
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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