| 摘要 |
PURPOSE:To eliminate a DC preventing capacitor and to miniaturize a circuit, by preventing the application of the DC voltage to a variable resistance element when a transistor, etc. is used to said resistance element. CONSTITUTION:The difference of potential is set at nearly zero between points (a) and (b) of a transistor (TR)5. If the current IC of a control terminal 4 is set at zero, the resistance value between the collector and the emitter of the TR5 is set an extremely high level. Then the input signal current Ii flows into the base of a TR9 virtually as it is and amplified to emerge at an output terminal 12 in the form of the output voltage signal. With increment of the current IC, the collectore-emitter resistance value of the TR5 reduces. Then the current Ii flows also to the TR5, and as a result, the voltage given from the terminal 12 also reduces. In such way, the degree of amplification is controlled. |
