| 摘要 |
PURPOSE:To obtain a stable amplifier, by changing an opened loop gain simultaneously with the change of the negative feedback rate so that the changed feedback quantity becomes constant. CONSTITUTION:An input voltage is given to an inversion input 35 of an amplifier 34 from an input terminal 37 of an opened loop system, and a voltage is given to a noninversion input 36 from a feedback circuit consisting of a variable resistance Rf and a fixed resistance Re. The collector terminal of the last-stage transistor TR38 is the output of a closed loop system. The variable resistance Rf is a part of the load resistance of the TR38; and since the gain of the last stage is changed in proportion to the value of the variable resistance Rf in case of Re<<Rf, an opened loop gain A of the circuit is proportional to the value of the resistance Rf. A feedback rate beta and the opened loop gain A satisfy equation Abeta=(R2+1)/4R-(1/2) (R is the stagger ratio of the amplifier), and the opened loop gain A and the feedback rate beta are changed simultaneously by changing the value of the resistance Rf to make a negative feedback quantity 1+Abeta constant. |
