Touch panel and driving method of the same

Abstract

It is an object to provide a touch panel which includes an A/D converter circuit and has a function of image shooting with high resolution and high-level gray scale and at high operation speed. A touch panel includes a plurality of pixels each provided with a display element and a photo sensor, an A/D converter to which a first potential is applied from a photo sensor, and a reading circuit. The A/D converter includes an oscillation circuit which changes the oscillating frequency of a first signal to be generated in accordance with the first potential and stops oscillating when a second potential is applied thereto from the reading circuit, and a counter circuit which generates a second signal having a discrete value determined in accordance with the oscillating frequency.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising:
 a photo sensor;   an oscillation circuit operationally connected to the photo sensor; and   a counter circuit operationally connected to the photo sensor, the counter circuit operationally connected to an output terminal of the oscillation circuit,   wherein the counter circuit is capable of generating a first signal having a discrete value,   wherein the oscillation circuit is capable of generating a second signal having an oscillation frequency, and   wherein the discrete value is determined by a signal from the photo sensor.   
     
     
         3 . The semiconductor device according to  claim 2 , wherein the second signal is determined by the signal from the photo sensor. 
     
     
         4 . The semiconductor device according to  claim 2 , wherein the discrete value is determined by the oscillation frequency. 
     
     
         5 . The semiconductor device according to  claim 2 , wherein a period from when the oscillation circuit starts oscillating to when the second signal has a toggle is approximately half an oscillation cycle of the oscillation circuit. 
     
     
         6 . The semiconductor device according to  claim 2 , wherein the photo sensor comprises a photo diode. 
     
     
         7 . The semiconductor device according to  claim 2 , further comprising:
 a transistor including a semiconductor film, the semiconductor film formed on a surface,   wherein the photo sensor is formed on the surface.   
     
     
         8 . A touch panel comprising the semiconductor device according to  claim 2 . 
     
     
         9 . An electronic device comprising the touch panel according to  claim 8 . 
     
     
         10 . A semiconductor device comprising:
 a photo sensor;   an oscillation circuit operationally connected to the photo sensor; and   a counter circuit operationally connected to the photo sensor, the counter circuit operationally connected to an output terminal of the oscillation circuit,   wherein the counter circuit is capable of generating a first signal having a discrete value,   wherein the oscillation circuit is capable of generating a second signal having an oscillation frequency,   wherein the discrete value is determined by a signal from the photo sensor, and   wherein the photo sensor includes a stacked structure vertically.   
     
     
         11 . The semiconductor device according to  claim 10 , wherein the second signal is determined by the signal from the photo sensor. 
     
     
         12 . The semiconductor device according to  claim 10 , wherein the discrete value is determined by the oscillation frequency. 
     
     
         13 . The semiconductor device according to  claim 10 , wherein a period from when the oscillation circuit starts oscillating to when the second signal has a toggle is approximately half an oscillation cycle of the oscillation circuit. 
     
     
         14 . The semiconductor device according to  claim 10 , wherein the photo sensor comprises a photo diode. 
     
     
         15 . The semiconductor device according to  claim 10 , further comprising:
 a transistor including a semiconductor film, the semiconductor film formed on a surface,   wherein the photo sensor is formed on the surface.   
     
     
         16 . A touch panel comprising the semiconductor device according to  claim 10 . 
     
     
         17 . An electronic device comprising the touch panel according to  claim 16 .