| 摘要 |
PURPOSE:To reproduce an input voice signal in an excellent way by devising a voltage across speaker coil terminals to be a voltage proportional to an input voice signal in the amplifier circuit used for a speaker driving circuit even when the speaker generates power. CONSTITUTION:An operational amplifier 2 is employed to compare an input voice voltage with an output voltage. That is, the output voltage is divided by using resistors 4,5 for the comparison with the input voltage and a voltage amplification factor.of the operational amplifier 2 is selected to be the unity. Concretely, a conventional resistor is used for the resistor 4 and a DC component resistance of a speaker is used for the resistor 5, and then a voltage amplification factor of a differential amplifier 1 is selected to be the unity by. the resistance as resistance of the resistors 4, 5/resistance of the resistor 5. A forward electromotive force is produced in the speaker 3 by driving the speaker 3 with the amplifier circuit formed as above, a voltage across the resistor 5 and the input voltage are compared with the amplifier 2 to feed back the inverted forward electromotive force to the amplifier 1. Thus, forward electromotive force and counter electromotive force produced in the speaker 3 are apparently cancelled producing a voltage proportional to the input voltage between speaker coil terminals. |
