Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-11-12
2001-08-14
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000
Reexamination Certificate
active
06275210
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a driver circuit of a liquid crystal display device (hereinafter referred to as an LCD) and, more specifically, to a driver circuit of a matrix type LCD having a data latch circuit for latching digital input data in response to sampling pulses that are generated based on horizontal scanning.
Under the current technologies, in producing what is called a driver circuit integration type LCD in which a driver circuit system is formed by using polysilicon TFTs (thin-film transistors) so as to be integral with a pixel (liquid crystal) system, a high power supply voltage and a high clock pulse voltage are necessarily required because the characteristics of a polysilicon TFT are inferior to those of a single crystal silicon transistor. Typically, a power supply voltage VDD is set higher than 13 V.
At present, low power consumption type mobile computers are being developed and commercialized actively. For an LCD to be used for this purpose, it needs to satisfy a condition of low power consumption. However, as described above, an LCD consumes large power when VDD is set higher than 13 V, for example. Further, since an input timing system needs a high voltage, it is necessary to effect voltage increase from an input voltage of the TTL level or the 2.7-V system to a voltage of the 13-V system inside or outside the LCD panel. Therefore, in the aspect of the system configuration, the use of a booster circuit causes increase in circuit scale and power consumption but also undesired emission.
On the other hand, where the common inversion driving method is used which is a commonly known liquid crystal driving method, a dynamic range of about 5 V is sufficient for a driver circuit system. The common inversion driving method is a driving method which can approximately halve the effective voltage of an external input video signal by varying the opposed electrode voltage with a phase opposite to that of the input signal. Although the common inversion driving method is a promising method for reducing the power consumption of mobile LCDs, the driver circuit system is a major factor of obstructing development of low power consumption LCDs because of insufficient device performance.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems in the art, and an object of the invention is to provide a driver circuit which can contribute to reduction in the power consumption of a liquid crystal display device.
The invention provides a liquid crystal display device having a data latch circuit for latching digital input data in response to a sampling pulse signal that is generated based on horizontal scanning, the data latch circuit comprising a comparator section having a PMOS differential circuit that receives the digital input data as an input for comparison and a predetermined comparison reference voltage as an input for reference, for performing a comparison operation in a sampling period of the sampling pulse signal; a first data latch section for latching an output of the comparator section in a non-sampling period of the sampling pulse signal; and a second data latch section for latching output data of the first data latch section in response to an output enable pulse occurring in one horizontal period.
The liquid crystal display device may be of a type further having a shift register and a decoder circuit.
According to another aspect of the invention, there is provided a driver circuit of a liquid crystal display device having a data latch circuit for latching digital input data in response to a sampling pulse signal that is generated based on horizontal scanning, the data latch circuit comprising a comparator section having a PMOS differential circuit that receives the digital input data as an input for comparison and a predetermined comparison reference voltage as an input for reference, for performing a comparison operation in a sampling period of the sampling pulse signal; a first data latch section for latching an output of the comparator section in a non-sampling period of the sampling pulse signal; and a second data latch section for latching output data of the first data latch section in response to an output enable pulse occurring in one horizontal period.
In the above-configured liquid crystal display device or driver circuit, the comparator section converts digital input data of, for example, the 2.7-V system into data of a power supply voltage level by comparing it with a comparison reference voltage by using the PMOS differential circuit. The converted data is latched by the first data latch section in a non-sampling period of a sampling pulse signal. The data latched by the first data latch section is then held for a 1H period (one horizontal period) by the second data latch section.
REFERENCES:
patent: 5739805 (1998-04-01), Dingwall
patent: 6067066 (2000-05-01), Kubota et al.
patent: 6078318 (2000-06-01), Hori et al.
Ghausi, M.S. “Electronic Devices and Circuits” Holt, Rinehart and Winston p. 399, 1985.
Hjerpe Richard
Kananen Ronald P.
Nguyen Francis
Rader Fishman & Grauer
Sony Corporation
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