A position indicating implement is disclosed having a first coil connected to a current source and a second coil inductively coupled with the first coil. A capacitor is connected in series with the second coil so that the current in the first coil induces a phase shifted current in the second coil. A...http://www.google.com.tw/patents/US4638119?utm_source=gb-gplus-share專利 US4638119 - Position indicating apparatus for use in a digitizing tablet system
