| 摘要 |
PURPOSE: A variable gain and low noise amplifier is provided to perform an optimum performance at each gain mode by not affecting the performance of the circuit which is optimally operated at the different gain mode. CONSTITUTION: A variable gain and low noise amplifier includes a first amplification cell(3100), a second amplification cell(3300), a selective matching circuit(3500) and a first switch(SW1). The first amplification cell(3100) is provided with a first terminal and a second terminal connected to the output terminal and amplifies the signal applied to the first terminal at a high gain mode to the second terminal. The second amplification cell(3300) is provided with a first terminal and a second terminal connected to the output terminal and amplifies the signal applied to the first terminal at a low gain mode to the second terminal. The selective matching circuit(3500) is provided with a first terminal connected to the input terminal and a second terminal connected to the first terminal of the first amplification cell(3100) to selectively change the input impedance of the first amplification cell(3100). And, the first switch(SW1) is connected to the input terminal and the first terminal of the second amplification cell(3300) to transmit the signal applied to the input terminal during the operation of the low gain mode to the first terminal of the second amplification cell(3300).
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