Method for measuring distance between coordinate indicator and coordinate input device

A coordinate input device, comprising a master controller, a slave controller, a signal generator, a damping circuit, a second analog multiplexer, transmit coils, receiving coils, a first analog multiplexer, a gain control circuit and a measurement circuit, wherein

• the slave controller is configured to control the signal generator and the second analog multiplexer to excite a transmit coil in accordance with an instruction from the master controller, the transmit coil is excited to transmit an electromagnetic signal, and the receiving coil is configured to receive the electromagnetic signal sensed and sent back from a coordinate indicator and output an output signal;
• the measurement circuit is configured to measure an actual amplitude of the output signal of the receiving coil which have passed through the first analog multiplexer and the gain control circuit, the actual amplitude of an output signal of the receiving coil being measured 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;
• the slave controller is further configured to transmit a measurement signal 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, one of preset nominal amplitudes corresponding to a plurality of preset magnification factors of the receiving coil is selected in accordance with an amplitude of the measurement signal as a nominal amplitude for the measurement signal;
• the damping circuit is configured to control the amplitude of the measurement signal so that the amplitude of the measurement signal corresponds to the actual amplitude of the output signal of the receiving coil;
• the measurement circuit is further configured to determine a nominal amplitude for the output signal of the receiving coil corresponding to one of the preset magnification factors of the receiving coils in accordance with the actual amplitude of the output signal;
• and
• the master controller is configured to control the gain control circuit to adjust the actual amplitude of the output signal of the receiving coil, and to set a reference signal amplitude as the determined nominal amplitude for the output signal, wherein the distance between the coordinate indicator and the coordinate input device is determined in accordance with the actual amplitude of the output signal, the nominal amplitude for the measurement signal, and the set reference signal amplitude.