PURPOSE: To obtain a small-sized digitizer which can suppress external noises other than a specific ultrasonic wave signal for coordinate detection and discriminate whether a detected ultrasonic wave signal is normal or a noise.
CONSTITUTION: The coordinate detecting device consists of a coil 1 which detects an electromagnetic wave signal from a coordinate indicator and generates a synchronizing signal from this detected signal, a resonance circuit 2, an amplifying circuit 3 and a pulse shaping circuit 4, a microphone 8 which detects the ultrasonic wave signal from the coordinate indicator, an amplifying circuit 9, a band-pass filter 10, a comparator 11 and a waveform detecting circuit 12, an oscillation circuit 5 for detecting the delay time of the synchronizing signal up to the ultrasonic wave signal detection, a counter 6, and a latch 13. Then a threshold value signal generating circuit 7 which generates a threshold value signal of the comparator 11 by using the synchronizing signal is provided between the pulse shaping circuit 4 and comparator 11.
TANIOKA TAKASHI
ISHIDA TAKASHI
HASUNUMA KAZUHISA
