| 摘要 |
PURPOSE:To prevent an offset voltage at no input from being caused by inverting a current obtained in response to an input voltage at a current mirror circuit and causing the current to flow to a level shift transistor (TR). CONSTITUTION:An AC signal is compressed by a 1/2 power amplifier 4, converted into a half rectifier voltage at a signal converting circuit 6 and the result is inputted to a level shift circuit 8. A collector current I1 of an input TR 44 of the level shift circuit 8 is converted into a current value K.I1 by the mirror circuit 50. The current is branched to an emitter of a TR 48 and a base of a TR 16. As a result, a DC current I2 in response to an input DC voltage flows to the TR 16 and a level shift output given by R22.I2 is obtained across a resistor 22. That is, since the current flowing to the TR 44 at no input is zero, the base-emitter voltage of the TR 48 is zero and the TR 16 is completely turned off, allowing to prevent an offset voltage from being caused.
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