Patent ID: 7277684

Claim:
An antenna amplifier which is to be disposed in a vicinity of an antenna, for amplifying a weak high-frequency signal received by the antenna, the antenna amplifier comprising: a filter operable to receive a high-frequency signal from the antenna, operable to select a frequency band of the received high-frequency signal, and operable to output a high frequency signal of the selected frequency band; an amplifier connected to the filter, the amplifier being operable to amplify the high-frequency signal outputted from the filter; a through-circuit connected with the filter, the through-circuit being operable to guide the high-frequency signal outputted from the filter, without passing through the amplifier; a switch circuit connected to an output of the amplifier and an output of the through-circuit, the switch circuit being operable to switch between a high-frequency signal outputted from the amplifier and the high-frequency signal guided through the through-circuit; and an output switchover circuit, which in response to an output of the amplifier and in accordance with a level relationship of the output with respect to a predetermined switchover criterion, is operable to control the switch circuit to be switched to a side of the output of the amplifier when the output is lower, and to be switched to a side of the through-circuit when the output is higher, wherein a level detection for switching is performed between the amplifier and the switch circuit, wherein the amplifier has a negative feedback configuration, and wherein, in a case of an input of a high level, an output of the amplifier is opened, whereby distortion of the amplifier itself is reduced and distortion which is generated in an input portion is eliminated.