| 摘要 |
PROBLEM TO BE SOLVED: To stabilize AGC operation by avoiding inconvenience, where monotonicity in gain change characteristics is lost, in a gain-variable amplifier whose gain variable range is increased. SOLUTION: A variable current source 20 controls control currents IB1-IB5 allowed to flow to initial stages LNA1-5, based on a control voltage VAGC of gain adjustment. When the control voltage VAGC for setting gain to not less than about 0[dB] is input, the variable current source 20 performs control so that the total value of the control currents IB1-IB5 flowing to the initial stages LNA1-5 simultaneously is fixed at a prescribed value. When the control voltage VAGC for setting the gain to less than about 0[dB] is input, the variable current source 20 performs control so that the total value of the control currents IB1-IB5 flowing to the initial stages LNA1-5 simultaneously becomes smaller than the prescribed value, thus preventing an excessive control current from being supplied to the amplitude of an input signal, where the level is attenuated by attenuators 11-14, and hence avoiding inconvenience where monotonicity in the gain change characteristics is lost. COPYRIGHT: (C)2009,JPO&INPIT
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