| 摘要 |
PURPOSE:To widen the band of a variable gain amplifying circuit used for an optical repeater, by powering up two differential couples of transistors (TR), exercising voltage control over the outputs of a differential couple of TRs, through a TR for compensating the variation of an operation point. CONSTITUTION:An input signal IN is applied to the bases of TRs Q6 and Q7 and an output signal OUT is obtained at the collectors of TRs Q8 and Q11 among differential couples of TRs Q8-Q11 connected to the collectors of the TRs Q6 and Q7; and a reference voltage Vr is applied to the bases of the TRs Q8 and Q11, a control voltage Va is applied to the bases of the TRs Q8 and Q10, and a bias voltage Vb is applied to the base of the TRQ12 as a current source. The emitter of a TRQ13 for compensating operation-point variation is connected to resistances (R) 4 and 5, the base is connected to collector connection points between the R7 and TRs Q9 and Q10, and the collector is connected to a power source. The resistance value of the R7 is set a half those of the Rs 4 and 5 to obtain a wide-band variable gain amplifying circuit suitable for IC- implementation. |
