POSITION DETECTOR FILTERING SENSED FINGER AND STYLUS SIGNALS IN SYNCHRONIZATION WITH DISPLAY REFRESH

摘要

A position detecting device detects both a finger and a stylus radiating an electric field. The device includes: a substantially transparent sensor disposed on a display device and formed by X-electrodes and Y-electrodes; an X-selecting circuit for selecting two sets of X-electrodes as a positive terminal and a negative terminal; a Y-selecting circuit for selecting two sets of Y-electrodes as a positive terminal and a negative terminal; a driving signal generating circuit for generating signals shifted in phase from each other by 180° as a positive signal and a negative signal; a differential amplifier for amplifying a difference between signals occurring in the positive terminal and the negative terminal selected by one, or respectively each, of the X-selecting circuit and the Y-selecting circuit; and a balanced switching circuit for switching connection of the positive terminal and the negative terminal to the driving signal generating circuit or to the differential amplifier.

主权项

1. A position detector, comprising:
a display which is refreshed in response to refresh signals; a sensor disposed over the display and composed of first electrodes extending in a first direction and second electrodes extending in a second direction different from the first direction; sensor control circuitry which is coupled to the sensor and which, in operation, supplies signals of a first frequency to the first electrodes, detects a finger in contact with the sensor based on signals of the first frequency sensed by the second electrodes, and detects a position on the sensor indicated by a stylus generating an electric field of a second frequency different from the first frequency based on signals of the second frequency sensed by the first electrodes and signals of the second frequency sensed by the second electrodes; and filter circuitry which, in operation, receives signals sensed by the first electrodes and signals sensed by the second electrodes and selectively outputs signals corresponding to the first frequency and signals corresponding to the second frequency to the sensor control circuitry according to control signals received from the sensor control circuitry; wherein, the sensor control circuity, in operation, sends the control signals to the filter circuity at timings synchronized with the refresh signals that refresh the display.