| 摘要 |
PURPOSE:To minimize the production of shot noise due to unnecessary idling current, by adjusting the idling current with an input signal current. CONSTITUTION:The output of an operational amplifying circuit 1 to which the input signal IN is fed from the inverting input terminal, is level-shifted to positive and negative direction with the level shift means 2 and 3, and they are respectively fed to circuit connecting points T1, T2, and the signal IN is fed to the collector of transistors (TR) Q1, Q2. Further, the output OUT is obtained by making common the collector of TRs Q3, Q4. With the circuit constitution like this, the means 2 and 3 can be made adjustable according to the input signal current iIN maximum value as the variable constant voltage means. Between said means 2, 3 and the circuit connecting points T2, T3, resistors R1 and R2 are respectively provided, to set the DC voltage by the means 2 and 3 and the idling current Ii of TRsQ1-Q4 constituting the gain control section flowing through the connecting points T1, T2. Thus, the current Ii can be set to minimized value according to the current iIN to improves S/N. |
