| 摘要 |
PURPOSE:To obtain a feedback amplifier which makes it possible to ignore the non- linearity of its component capacitor and the influences of an internal series resistance and a high-frequency loss and then improve characteristics. CONSTITUTION:An input signal is supplied to non-inversion input terminal 32 of differential amplifier 31, one terminal of capacitor 34 is connected to inversion input terminal 33, and feedback circuit 36 of a two-terminal impedance network is connected between the other terminal of capacitor 34 and output terminal 35 of differential amplifier circuit 31. Here, the two-terminal impedance network is made adequate for the frequency equivalent of RIAA or NAB. Resistance 37 is connected to the other terminal of capacitor 34 and the earth, and resistance 37 and capacitor 34 constitute another feedback circuit. Between terminals 33 and 35 of circuit 31, DC feedback resistance 38 is connected. The value of resistance 38 is set much larger than the maximum value of the impedance value at the audio frequency of circuit 36. Therefore, the input impedance of circuit 31 is high and the value of resistance 38 is much larger than that of circuit 36; and almost all output current of circuit 31, therefore, flows to the earth via circuit 36 and resistance 37, so that a current flowing to capacitor 34 can be suppressed low. |
