| 摘要 |
PURPOSE:To exercise wide-range gain control by varying the gain of a differential amplifier through diodes, whose conduction resistance vary with an AGC voltage, for the intermediate-frequency gain control of an IC-impelemented AM radio set. CONSTITUTION:An AGC voltage obtained from an AGC voltage circuit 2, which controls the gain of the intermediate-frequency amplification stage of an IC-implemented AM radio flows from a current-source transistor (TR)T6 to a suction TRT7 through a middle point (a) between diodes (d)1 and 2 and another middle point (b) between Ds 3 and 6. Conduction resistances of the D1-D4 vary with the current flowing through the TRT6. Those D1-D4 are connected between input terminals of TRs T1 and T2 constituting a differential amplifier. Therefore, when the conduction resistances of the D1-D4 are nearly zero, the gain is zero and when extremely large, on the other hand, the largest gain is obtained. Thus, wide-range gain control is exercised. |
