Coordinates input system

A coordinates input system having a tablet constituting a coordinates input portion, a position designating device such as a stylus pen, and a position detection circuit adapted to drive said tablet and detect a position at which coordinates are input by said position designating device, said system comprising:

• a plurality of tuning circuits disposed in said position designating device, each of said plurality of tuning circuits including a coil and a capacitor to constitute a set and being adapted to transmit radio waves with mutually equivalent tuning frequencies and different phases in response to an external signal;
• switching means disposed in said position designating device and adapted to turn ON and OFF the connection between said coil and said capacitor of each of said tuning circuits;
• and
• an antenna coil disposed around a coordinates input range of said tablet;
• wherein radio waves are generated by said antenna coil when an AC signal of a frequency identical with that of said tuning frequency is intermittently applied to said antenna coil, and the status of the position and operation of said position designating device is detected when signals responded to by said tuning circuits during suspension of transmission of said radio waves are received by said antenna coil, and
• the ON-OFF status of said switching means with respect to said tuning circuits is discriminated by means of input signals having mutually different phases with respect to output signals of said antenna coil.

A coordinates input system having a tablet constituting a coordinates input portion, a position designating device such as a stylus pen, and a position detection circuit adapted to drive said tablet and detect a position at which coordinates are input by said position designating device, said system comprising:

• a tuning circuit disposed in said position designating device, said tuning circuit including a set of a coil, a capacitor, and/or a resistor and being adapted to generate radio waves with mutually equivalent tuning frequencies and a change in the phase in response to an external signal by changing any of the values of said coil, said capacitor, and/or said resistor in correspondence with the status of use of said position designating device;
• and
• an antenna coil disposed around a coordinates input range of said tablet;
• wherein radio waves are generated by said antenna coil when an AC signal of a frequency identical with that of said tuning frequency is intermittently applied to said antenna coil, and the status of the position and operation of said position designating device is detected when signals responded to by said tuning circuit during suspension of transmission of said radio waves are received by said antenna coil, and
• the status of use of said position designating device is discriminated by means of input signals having mutually different phases with respect to output signals of said antenna coil.