| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain circuit suppressing noises generated in a circuit generating a control output voltage for controlling a gain. SOLUTION: The variable gain circuit has two pairs of differential-pair transistors Q1 to Q4, a pair of first resistance elements R1 to R4 connected among ground terminals for these transistors, and a variable gain 120 with other paired differential transistors M1 and M2 imparting a pair of currents corresponding to an input differential signal Vin to two pairs of the paired differential transistors through the first resistance elements. The variable gain circuit further has a gain control unit 121 generating a pair of control output-voltage signals from the current corresponding to a control input-voltage signal Vdet and controlling a section between input terminals for two pairs of the paired differential transistors. In a voltage generator 122 generating a pair of the control output-voltage signals, a pair of second resistance elements R7 and R8 are connected to a pair of diodes Q5 and Q6. A pair of the second resistance elements are given characteristics corresponding to voltage-drop characteristics in a pair of the first resistance elements. COPYRIGHT: (C)2006,JPO&NCIPI
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