| 摘要 |
PURPOSE:To eliminate a noise generated between earth terminals by a simple constitution, by supplying a current of a constant ratio to the first transistor, and the second transistor of a reverse conducting type, providing these currents and other current supplying means of a constant ratio, and separating grounding points of both of them. CONSTITUTION:An earth separating circuit 5 consists of a pnp transistor (TR) Q1 to whose base a signal from a signal source 1 is inputted, an npn TR which makes its emitter output a base input, a current mirror circuit for supplying a current of a constant ratio to both of them, namely, a pnp TR Q4, a pnp TR Q3 having a common base with it, an resistances R2, R3. The collector of the TR Q1 is connected directly to the earth side of the signal source 1, and the emitter of the TR Q2 is connected to the earth side of the signal source 1 through a resistance R1. The current mirror circuit has the TR Q4 and a pnp TR Q5, whose bases are connected to each other, and a resistance R4, and a current of a constant ratio is outputted to a current of the former. This current is connected to the earth side of an amplifier 2 through resistances R5, R6. According to this constitution, a noise caused by earth impedance between an input and an output can be eliminated satisfactorily. |
