Driving circuit of display device

Abstract

A driving circuit of a display device including a TFT (Thin Film Transistor) liquid crystal display device or the like is provided which is capable of decreasing a chip in size and reducing costs of testing by reducing the number of bits even in the case of increased number of bits of digital image data to perform multi-gray shade displaying. The driving circuit of the display device has a gray shade voltage generating circuit adapted to generate a plurality of voltages, gray shade voltage selecting circuits used to select one voltage out of a plurality of voltages supplied from the gray shade voltage generating circuit based on high order bits composed of one or two and more bits counted from the most significant bit of the digital image data and the number of bits of which is smaller than that of the digital image data and to output it, operational amplifiers used to convert an impedance of a voltage outputted from gray shade voltage selecting circuits and voltage adjusting circuits used to induce a voltage rise or a voltage drop in voltages outputted from the operational amplifier based on low order bit of the digital image data excluding its high order bits.

1. A driving circuit of a display device for displaying a plurality of gray shades based on inputted digital image data comprising:
 gray shade voltage generating means for generating a plurality of voltages;  
 gray shade voltage selecting means for selecting one voltage out of a plurality of voltages supplied from said gray shade voltage generating means based on high order bits composed of at least one bit counted from the most significant bit of said digital image data, and for outputting said voltage;  
 an operational amplifier used to amplify a voltage outputted from said gray shade voltage selecting means; and  
 voltage adjusting means for inducing a voltage rise or a voltage drop of a voltage outputted from said operational amplifier based on low order bits of said digital image data.  
 
     
     
       2. The driving circuit of the display device according to  claim 1 , wherein said voltage adjusting means is comprised of a resistor, one end of which is connected to an output terminal of said operational amplifier, an active device connected to another end of said resistor and controlling means for controlling operations of said active device based on said low order bits of said digital image data, wherein said other end of said resistor is connected to said display device. 
     
     
       3. The driving circuit of the display device according to  claim 1 , wherein said active device has a first transistor, a drain of which is connected to said resistor, a source of which supply power is applied to and a gate voltage of which is controlled by said controlling means, and a second transistor a drain of which is connected to said resistor, a source of which is connected to a ground and a gate voltage of which is controlled by said controlling means. 
     
     
       4. The driving circuit of the display device according to  claim 1 , wherein said resistor is composed of an analog switch. 
     
     
       5. The driving circuit of the display device according to  claim 1 , wherein said gray shade voltage generating means is provided with two or more input terminals to which an voltage is inputted from outside and with dividing means used to divide voltages inputted into said input terminals into many voltages. 
     
     
       6. The driving circuit of the display device according to  claim 1 , wherein a voltage outputted from said gray shade voltage generating means is a positive polarity voltage and a negative polarity voltage. 
     
     
       7. The driving circuit of the display device according to  claim 1 , wherein, when bits of said digital image data are N, said high order bits are composed of (N−1) bits counted from the most significant bit of said digital image data and the low order bit is composed of one bit counted from the least significant bit of the digital image data. 
     
     
       8. A driving circuit of a display device for displaying a plurality of gray shades based on inputted digital image data comprising:
 a gray shade voltage generating circuit for generating a plurality of voltages;  
 a gray shade voltage selecting circuit for selecting one voltage out of a plurality of voltages supplied from said gray shade voltage generating circuit based on high order bits composed of at least one bit counted from the most significant bit of said digital image data, and for outputting said voltage;  
 an operational amplifier used to amplify a voltage outputted from said gray shade voltage selecting circuit; and  
 a voltage adjusting circuit for inducing a voltage rise or a voltage drop of a voltage outputted from said operational amplifier based on low order bits of said digital image data,  
 wherein said voltage adjusting circuit is comprised of a resistor, one end of which is connected to an output terminal of said operational amplifier, an active device connected to another end of said resistor and controlling circuit for controlling operations of said active device based on said low order bits of said digital image data, wherein said other end of said resistor is connected to said display device.  
 
     
     
       9. The driving circuit of the display device according to  claim 8 , wherein said active device has a first transistor, a drain of which is connected to said another end of said resistor, a source of which supply power is applied to and a gate voltage of which is controlled by said controlling circuit, and a second transistor a drain of which is connected to said another end of said resistor, a source of which is connected to a ground and a gate voltage of which is controlled by said controlling circuit. 
     
     
       10. The driving circuit of the display device according to  claim 8 , wherein said resistor is composed of an analog switch. 
     
     
       11. The driving circuit of the display device according to  claim 8 , wherein a voltage outputted from said gray shade voltage generating circuit is a positive polarity voltage and a negative polarity voltage. 
     
     
       12. The driving circuit of the display device according to  claim 1 , wherein, when bits of said digital image data are N, said high order bits are composed of (N−1) bits counted from the most significant bit of said digital image data and the low order bit is composed of one bit counted from the least significant bit of the digital image data. 
     
     
       13. A driver for driving a display device in response to a plurality of input data, each of said input data comprising a plurality of bits, said driving circuit comprising:
   a gray shade voltage generating circuit generating a plurality of gray shade voltages, the number of said gray shade voltages being determined by the number of said bits of said input data, said gray shade voltages being divided into first and second groups of gray shade voltages, said first group of gray shade voltages being generated by a resistance string circuit and said second group of gray shade voltages being generated based on at least two different ones of first group of gray shade voltages; and        a plurality of output terminals coupled to said display device, each of said output terminal being provided for an associated one of said input data and to supply said display device with one of said gray shade voltages responsive to information of the associated one of said input data.     
     
     
       14. The driver as claimed in  claim 13 , wherein said output terminal outputs one of said first group of gray shade voltages when said display device is driven with a first input data corresponding to a halftone region. 
     
     
       15. The driver as claimed in  claim 14 , wherein said output terminal outputs one of said second group of gray shade voltages when said display device is driven with a second input data corresponding to said halftone region. 
     
     
       16. The driver as claimed in  claim 15 , wherein said output terminal outputs one of said first group of gray shade voltages when said display device is driven with a third input data corresponding to a non- halftone region.   
     
     
       17. A driver for driving a display device in response to a plurality of input data, comprising:
   a gray shade voltage generator for generating a plurality of gray shade voltages;        a gray shade voltage selector, selecting without a voltage up or a voltage drop, a first one of said gray shade voltages when said display is driven with a first input data corresponding to a non - halftone region, selecting without a voltage up or a voltage drop, a second one of said gray shade voltages when said display is driven with a second input data corresponding to a halftone region, and selecting a voltage generated by a voltage up or a voltage drop of said second one of said gray shade voltages when said display is driven with a third input data corresponding to said halftone region; and        an amplifier amplifying a voltage outputted from said gray shade voltage selector.     
     
     
       18. The driver as claimed in  claim 17 , wherein said voltage generated by said voltage up or said voltage drop is generated by dividing according to said second one of said gray shade voltages and a voltage different from said second one.