| 摘要 |
PURPOSE:To attain stable AGC feedback by applying a fixed component and a variable component of a gain control current from separate current sources to eliminate the need for limitation to the variable range of a gain control voltage. CONSTITUTION:The current given to the 1st differential pair (transistors TRs 101, 102) and the 2nd differential pair (TRs 103, 104) is divided into the fixed component (1-alpha)I0 and the variable component alphaI0 required for the variable gain and the components are applied from separate current sources 401 and 112. That is, the maximum value of the variable component of an emitter current I1 is alphaI0 and the remaining (1-alpha)I0 is the minimum value of the fixed component. Then, the fixed component (1-alpha)I0 of the emitter current is supplied from the current source 401 and the variable component alphaI0 is supplied from the current source 112. The emitter current I1 given to the 1st differential pair (TRs 101, 102 and resistors 113, 114) is limited so as not to exceed alphaI0 (alpha=RE2/RE1+RE2). |
