Patent ID: 8797300

Claim:
A method for measuring a distance between a coordinate indicator including a resonating circuit and a coordinate input device provided with an electromagnetic induction plate including a transmit coil and a receiving coil, comprising: measuring an actual amplitude of an output signal of the receiving coil in the electromagnetic induction plate by a measurement circuit in the electromagnetic induction plate when the coordinate indicator performs a track input on the coordinate input device with a distance existing between the coordinate indicator and the coordinate input device, wherein the receiving coil outputs the output signal when it receives an electromagnetic signal that is transmitted by the transmit coil and then sensed and sent back by the resonating circuit of the coordinate indicator; selecting a nominal amplitude for the output signal from preset nominal amplitudes corresponding to preset magnification factors of the receiving coil, wherein the selected nominal amplitude for the output signal corresponds to one of the preset magnification factors in accordance with the actual amplitude of the output signal; setting a reference signal amplitude as the selected nominal amplitude; sending a measurement signal from the electromagnetic induction plate to the receiving coil, wherein the measurement signal simulates an electromagnetic signal received by the receiving coil when the coordinate indicator approaches or moves away from the coordinate input device; selecting one of the preset magnification factors of the receiving coil in accordance with the amplitude of the measurement signal; selecting one of the preset nominal amplitudes corresponding to the selected magnification factor as a nominal amplitude for the measurement signal; and determining the distance between the coordinate indicator and the coordinate input device in accordance with the actual amplitude of the output signal, the nominal amplitude for the measurement signal, and the set reference signal amplitude.