| 摘要 |
PURPOSE:To prevent the side tone to make a circuit into an IC by providing a capacitor which cancels inductance components of the characteristics impedance of a transmission line including a transformer to which a microphone and a speaker are connected. CONSTITUTION:The audio signal inputted from a microphone 11 is inputted to an amplifier 7 and an inverting amplifier 8 and is transmitted to an exchange 12 through a transformer 2. The audio signal transmitted from the exchange 12 is taken out by a differential amplifier 3 after passing the transformer 2, and the differential voltage is divided by impedances Z1 and Z2 and is given to a differential amplifier 4 and is amplified and is applied to a speaker 10. A characteristic impedance ZL of the transmission line including impedances Z0, Z1, and Z2 and the transformer 2 constitutes a bridge circuit. The impedance Z1 consists of a series circuit of a resistance and a capacitor, and inductance components of the impedance ZL are cancelled by this capacitor. Thus, the side tone is prevented to make the circuit into an IC. |
