| 摘要 |
An amplifier with substantially fixed input impedance being operated in a plurality of gain modes. The amplifier includes an input port for receiving an input signal, an amplifying circuit for amplifying the input signal with corresponding amplifying ratios in various gain modes, a plurality of resistive negative feedback circuits electrically connected to the input port and the amplifying circuit for keeping the input impedance substantially fixed in various gain modes, and an output port for outputting the input signal processed by the amplifying circuit.
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