| 摘要 |
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. |
