Liquid crystal display device and method for driving the same

A liquid crystal display device comprising:

• an array substrate and a counter substrate facing each other and including a liquid crystal layer interposed between the array substrate and the counter substrate;
• a display area formed of the array substrate, the counter substrate and the liquid crystal layer and including a plurality of pixels arranged in a matrix;
• a plurality of signal lines arranged along the pixels in a column direction;
• a plurality of scan lines arranged along the pixels in a row direction;
• a pixel electrode connected to each of the pixels, the pixel electrode being connected to the signal line through a pixel switch;
• a common electrode formed on the counter substrate and facing the pixel electrode;
• a driving unit connected to the signal lines and the scan lines to drive the plurality of pixels;
• a signal line driving circuit formed in the driving unit to sequentially apply an image signal and a non-image signal to the signal lines;
• a scan line driving circuit formed in the driving unit to conduct an image signal write-in operation and a non-image signal write-in operation in a vertical scan period;
• an auxiliary capacitance provided to each pixel to interpose an auxiliary capacitance signal to the pixel electrode;
• a plurality of auxiliary capacitance lines arranged along the pixels in a row direction and connected to the respective auxiliary capacitances of the pixels;
• and
• an auxiliary capacitance line driving circuit formed in the driving unit;
• wherein the auxiliary capacitance line driving circuit changes the auxiliary capacitance signal to the same polarity side of the image signal and the non-image signal after finishing the write-in operations of the image signal and the non-image signal to the selected pixel;
• wherein the auxiliary capacitance line driving circuit supplies a first voltage, a second voltage smaller than the first voltage and a third voltage smaller than the second voltage to the auxiliary capacitance lines, and the voltage difference between the first voltage and the second voltage is smaller than that between the second voltage and the third voltage;
• wherein the non-image signal is applied to the signal line to display black;
• wherein the pixel switch includes a gate electrode connected to the scan line, a source electrode connected to the corresponding signal line and a drain electrode connected to the pixel electrode;
• wherein the image signal and the non-image signal are written into the pixel electrode through the pixel switch and a common voltage is supplied to the common electrode;
• wherein the common voltage corresponds to respective center voltages of the image signal, the non-image signal and a voltage applied to the liquid crystal layer;
• wherein the voltage values are given so as to satisfy a following expression:
• (V2−(V1+V3)/2)×Cst/Ctot=ΔVg×(Cgd/Ctot),
• wherein,
• V1, V2 and V3 are first, second and third voltages, respectively;
• Cst is an auxiliary capacitance value;
• Cgd is a capacitance value generated between the gate electrode and the drain electrode when the pixel switch is “OFF”;
• Ctot is sum of a liquid crystal capacitance, an auxiliary capacitance value Cst, a capacitance generated between the source electrode and the drain electrode and the capacitance value Cgd;
• ΔVg is voltage difference between “ON” voltage and “OFF” voltage of the pixel switch.

A liquid crystal display device comprising:

• an array substrate and a counter substrate facing each other;
• a liquid crystal layer interposed between the array substrate and the counter substrate;
• a display area formed of the array substrate, the counter substrate and the liquid crystal layer and including a plurality of pixels arranged in a matrix;
• a plurality of signal lines and scan lines arranged in matrix, the pixels being located near intersections between the signal lines and the scan lines;
• a driving unit to drive the plurality of pixels connected to the signal lines and the scan lines;
• a pixel electrode provided to each pixel;
• a common electrode formed on the counter substrate and facing the pixel electrode;
• an auxiliary capacitance provided to each pixel to interpose an auxiliary capacitance signal to the pixel electrode;
• and
• auxiliary capacitance lines arranged along the pixels in a row direction and connected to the auxiliary capacitance of the respective pixels;
• wherein the respective auxiliary capacitances of adjacent pixels arranged in the row direction are connected to different auxiliary capacitance lines respectively;
• wherein the driving unit includes an auxiliary capacitance line driving circuit to supply a first voltage, a second voltage smaller than the first voltage and a third voltage smaller than the second voltage to the auxiliary capacitance lines, and the voltage difference between the first voltage and the second voltage is smaller than that between the second voltage and the third voltage;
• wherein the pixel switch includes a gate electrode connected to the scan line, a source electrode connected to the corresponding signal line and a drain electrode connected to the pixel electrode;
• wherein an image signal and a non-image signal are written into the pixel electrode through the pixel switch and a common voltage is supplied to the common electrode;
• wherein the common voltage corresponds to respective center voltages of the image signal, the non-image signal and a voltage applied to the liquid crystal layer;
• wherein the voltage values are given so as to satisfy a following expression:
• (V2−(V1+V3)/2)×Cst/Ctot=ΔVgx(Cgd/Ctot),
• wherein,
• V1, V2 and V3 are first, second and third voltages, respectively;
• Cst is an auxiliary capacitance value;
• Cgd is a capacitance value generated between the gate electrode and the drain electrode when the pixel switch is “OFF”;
• Ctot is sum of a liquid crystal capacitance, an auxiliary capacitance value Cst, a capacitance generated between the source electrode and the drain electrode and the capacitance value Cgd;
• ΔVg is voltage difference between “ON” voltage and “OFF” voltage of the pixel switch.

A method for driving a liquid crystal display device including a liquid crystal layer and a plurality of pixels arranged near intersections between signal lines and scan lines in a matrix, comprising:

• providing a driving unit to drive the plurality of pixels each having a pixel switch connected to the signal line and the scan line;
• forming auxiliary capacitances in the respective pixels;
• providing auxiliary capacitance lines arranged along the pixels and connected to the auxiliary capacitances;
• supplying a first voltage, a second voltage smaller than the first voltage, a third voltage smaller than the second voltage to the auxiliary capacitance lines, and the voltage difference between the first voltage and the second voltage being smaller than that between the second voltage and the third voltage;
• wherein the pixel includes the pixel switch connected to a pixel electrode, the pixel switch including a gate electrode connected to the scan line, a source electrode connected to the corresponding signal line and a drain electrode connected to the pixel electrode;
• wherein an image signal is written into the pixel electrode through the pixel switch and a common voltage is supplied to a common electrode;
• wherein the common voltage corresponds to respective center voltages of the image signal and a voltage applied to the liquid crystal layer;
• wherein the voltage values are given so as to satisfy a following expression:
• (V2−(V1+V3)/2)×Cst/Ctot=ΔVgx(Cgd/Ctot)
• wherein,
• V1, V2 and V3 are first, second and third voltages, respectively;
• Cst is an auxiliary capacitance value;
• Cgd is a capacitance value generated between the gate electrode and the drain electrode when the pixel switch is “OFF”;
• Ctot is sum of a liquid crystal capacitance, an auxiliary capacitance value Cst, a capacitance generated between the source electrode and the drain electrode and the capacitance value Cgd;
• ΔVg is voltage difference between “ON” voltage and “OFF” voltage of the pixel switch.