Patent ID: 7560990

Claim:
A low noise amplifier for operating in response to one of a first gain mode and a second gain mode, comprising: a voltage adjusting circuit, for providing a first bias voltage during the first gain mode and providing a second bias voltage during the second gain mode, where the second bias voltage is different from the first bias voltage; and an amplifying circuit, coupled to the voltage adjusting circuit, for determining a first transfer characteristic according to the first bias voltage and thereby amplifying an input signal to generate an output signal according to the first transfer characteristic, and for determining a second transfer characteristic according to the second bias voltage and thereby amplifying the input signal to generate the output signal according to the second transfer characteristic, and the amplifying circuit comprising: a load; a plurality of first transistors and at least one second transistor, wherein each of the first transistors and the second transistor has a first node coupled to the load for generating the output signal, a second node coupled to the input signal for receiving the input signal and a third node coupled to the voltage adjusting circuit for receiving the first bias voltage during the first gain mode and receiving the second bias voltage during the second gain mode; a plurality of first switching devices, coupled between the first nodes of the first transistors and the load respectively, wherein each of the first switching devices controls its connected first transistor being coupled to or decoupled to the load; and a controlling module, coupled to the first switching devices, for controlling an on/off state of each of the first switching devices with respect to the first gain mode and the second gain mode.