Multi-touch recognition resistive touch screen for recognizing multi-touch coordinates through capacitor charging time

A multi-touch recognition resistive touchscreen comprising:

• a first resistive layer which comprises a plurality of first resistive stripes disposed parallel with one another;
• a second resistive layer which comprises a plurality of second resistive stripes disposed perpendicularly to the first resistive stripes and faces the first resistive layer;
• a plurality of X+ electrodes each disposed at one end of each of the first resistive stripes;
• a plurality of X− electrodes each disposed at the other end of each of the first resistive stripes;
• a plurality of Y+ electrodes each disposed at one end of each of the second resistive stripes;
• a plurality of Y− electrodes each disposed at the other end of each of the second resistive stripes;
• a plurality of Y+ stripe selection switches disposed corresponding one to one to the plurality of Y+ electrodes;
• a plurality of Y− stripe selection switches disposed corresponding one to one to the plurality of Y− electrodes;
• a Y+ capacitor connected at one end thereof to ground;
• a Y+ equal resistance line switch disposed between the Y+ capacitor and the Y+ stripe selection switch to determine whether the Y+ capacitor is connected at the other end thereof to the plurality of Y+ stripe selection switches;
• a Y− capacitor connected at one end thereof to ground;
• a Y− equal resistance line switch disposed between the Y− capacitor and the Y− stripe selection switch to determine whether the Y− capacitor is connected at the other end thereof to the plurality of Y− stripe selection switches;
• a Y+ capacitor voltage detection unit which measures voltage applied to the Y+ capacitor in a state in which the first resistive stripe and the second resistive stripe are in contact with each other by touch, a voltage VDD is applied to the X+ electrode of the first resistive stripe contacting the second resistive stripe;
• the Y+ stripe selection switch and the Y+ stripe selection switch of the second resistive stripe contacting the first resistive stripe are closed, and the other switches are all opened;
• a Y− capacitor voltage detection unit which measures voltage applied to the Y+ capacitor in a state in which the first resistive stripe and the second resistive stripe are in contact with each other by touch, a voltage VDD is applied to the X+ electrode of the first resistive stripe contacting the second resistive stripe;
• the Y− stripe selection switch and the Y− stripe selection switch of the second resistive stripe contacting the first resistive stripe are closed, and the other switches are all opened;
• a Y+capacitor charging time measuring unit which obtains a charge time taken until a charging level given as VC/VDD reaches a desired level when a voltage measured by the Y+ capacitor voltage detection unit is VC;
• a Y− capacitor charging time measuring unit which obtains a charge time taken until a charging level given as VC/VDD reaches a desired level when a voltage measured by the Y− capacitor voltage detection unit is VC;
• a Y+ equal resistance line operating unit which obtains an equal resistance line based on a value of (RV+RY+) using VC/VDD=1−e−t/((RV+RY+)YCconR), where the contacting first resistive stripe has resistance RV, the contacting second resistive stripe has resistance RY+, and t is charge time of the Y+ capacitor CconR obtained by the Y+ capacitor charging time measuring unit;
• a Y− equal resistance line operating unit which obtains an equal resistance line based on a value of (RV+RY−) using VC/VDD=1−e−t/((RV+RY−)·CconL), where the contacting first resistive stripe has resistance RV, the contacting second resistive stripe has resistance RY−, and t is charge time of the Y− capacitor CconL obtained by the Y− capacitor charging time measuring unit;
• and
• a touch coordinate calculating unit which searches for a point of intersection between the equal resistance line based on the value of (RV+RY+) and the equal resistance line based on the value of (RV+RY−).