Drive circuit for driving an image display unit

Abstract

A drive circuit has a judgement circuit for judging whether the magnitude of the input video data resides in a linear region or the non-linear region of characteristic of liquid crystal transmittance. When the vide data resides within the linear region, some of the output gray-scale voltage for the LCD are generated by interpolation of adjacent two of the gray-scale voltages generated by a voltage generator. The reduced gray-scale voltage taps reduces the circuit scale and the test procedures for the drive circuit.

1. A drive circuit for driving a display unit comprising:
 a gray-scale level voltage generator for generating a plurality of gray-scale level voltages, said gray-scale voltages corresponding to magnitudes of possible video data in one-to-one correspondence in a non-linear region of characteristic of liquid crystal transmittance and corresponding to magnitudes of possible video data in one-to-n correspondence in a linear region of characteristic of liquid crystal transmittance where n is an integer larger than one;  
 a gray-scale voltage selector block for responding to input video data to select one of said gray-scale level voltages;  
 a judgement section for judging whether a magnitude of an input video data resides within the non-linear region or the linear region to output a judgement signal indicating the non-liner region or the linear region; and  
 an output circuit for responding to said judgement signal to output said one of said gray-scale level voltages selected by said gray-scale voltage selector block when said judgment signal indicates the non-linear region and output one of said gray-scale voltages or an intermediate voltage when said judgement signal indicates the linear region, the intermediate voltage residing between two of adjacent gray-scale voltages.  
 
     
     
       2. The drive circuit as defined in  claim 1 , wherein given n is two. 
     
     
       3. The drive circuit as defined in  claim 1 , wherein said output circuit includes a modified voltage follower for generating one of said gray-scale voltages or an adjacent intermediate voltage, said modified voltage follower being controlled to equalize the input and output thereof or to differentiate the input and the output thereof by a specified voltage. 
     
     
       4. The drive circuit as defined in  claim 1 , wherein said judgement circuit includes a coincidence circuit for judging whether or not a plurality of significant bits of the video signal coincides. 
     
     
       5. The drive circuit as defined in  claim 1 , wherein given n is four. 
     
     
       6. The drive circuit as defined in  claim 5 , wherein said output circuit includes an interpolation circuit for generating a plurality of intermediate voltages between adjacent two of said gray-scale voltages. 
     
     
       7. The drive circuit as defined in  claim 6 , wherein said interpolation circuit includes a resistor string. 
     
     
       8. The drive circuit as defined in  claim 5 , wherein said judgement circuit includes a coincidence circuit for judging whether or not a plurality of significant bits of the video signal coincide with one another. 
     
     
       9. A driver for driving a display 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 generation 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;        a plurality of output terminals coupled to said display device; and        a plurality of selector circuits, each of said selector circuits selecting one of said gray shade voltages in response to information of an associated one of said input data, said one of said gray shade voltages being supplied to an associated one of said output terminals.     
     
     
       10. The driver as claimed in  claim 9 , further comprising at least two resistors for voltage dividing by using selected two voltages from first group of gray shade voltages to produce said second group of gray shade voltages. 
     
     
       11. The driver as claimed in  claim 10 , wherein said selector selecting an associated one of said first group of gray shade voltages when said display device is driven with a first input data corresponding to a non- linear region of characteristic of liquid transmittance, selecting an associated one of said first group of gray shade voltages when said display device is driven with a second input data corresponding to a linear region of characteristic of liquid transmittance, selecting an associated one of said second group of gray shade voltages when said display device is driven with a third input data corresponding to said linear region of characteristic of liquid transmittance.   
     
     
       12. A driver for driving a display device, comprising:
   a gray shade voltage generating circuit having a resistor string, said resistor string having a first portion producing a first group of gray shade voltages, said resistor string having a second portion producing a second group of gray shade voltages, said resistor string having a third portion between said first and second portions producing a third group of gray shade voltages;        a selector selecting an associated one of said first and third groups of gray shade voltages when said display device is driven with a first input data corresponding to said non - linear region of characteristic of liquid transmittance, selecting an associated one of said third group of gray shade voltages when said display device is driven with a second input data corresponding to a linear region of characteristic of liquid transmittance, selecting a gray shade voltage produced from associated two ones of said third group of gray shade voltages when said display device is driven with a third input data corresponding to said linear region of characteristic of liquid transmittance; and        an amplifier amplifying a gray shade voltage outputted from said selector to apply the amplified gray shade voltage to said display device.     
     
     
       13. The driver as claimed in  claim 12 , said selector including at least two resistors to perform a voltage dividing by using adjacent two gray shade voltages to generate said gray shade voltage produced from associated two ones.