| 摘要 |
A variable-gain amplifier that prevents the change in the in-phase voltage of the output occurring when the gain is changed and improves the frequency characteristic compared with the conventional method. The differential current of currents I13 and I13' changes corresponding to input signal S1. As a result, the differential current of currents I11 and I12 also change correspondingly, and the differential voltage v13 between nodes N1 and N2 varies. The gain of differential voltage v13 with respect to input signal S1 is variable corresponding to the current conversion gains of current converters 2 and 3. When the current conversion gains vary corresponding to the input signal S2, the voltages at nodes N1' and N2' are adjusted such that the voltages at nodes N1 and N2 are constant with respect to the change in gain. Since voltage-adjustment circuit 1 adjusts the voltages at nodes N1 and N2 via resistors R11 and R12, the deterioration in the frequency characteristic caused by the output capacitance of voltage-adjustment circuit 4 can be mitigated.
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