| 摘要 |
PURPOSE:To decrease the number of terminals of an integrated circuit by connecting an opening/closing switch for selecting sound quality and a capacitor for amplitude modulation to the same terminal of the integrated circuit and performing the detection of the opening/closing state of the opening/closing switch and the charging and discharging of the capacity through the same terminal. CONSTITUTION:The opening/closing switch SW1 which can be opened and closed is connected in series with the capacitor CC which imposes amplitude modulation on an acoustic signal and when a detecting circuit DT connected to the connection point between the opening/closing switch SW1 and capacitor CC judges that the opening/closing switch SW1 is open, a control circuit CR controls the charging and discharging the capacitor CC. The capacitor CC and opening/closing switch SW1 are formed outside the integrated circuit and connected to the same terminal TM1 of the integrated circuit within a broken line in a figure. Consequently, the number of terminals of the circuit can be decreased. |
