Patent ID: 7596361

Claim:
A low noise amplification circuit which amplifies signals by a predetermined gain, comprising: at least a low noise amplifier including an amplifying element, and a matching input circuit coupled to an input terminal of the amplifying element; and a filter coupled to an input terminal of the low noise amplifier, wherein when γ s represents a reflection factor, an impedance conversion for the γ s is set at a predetermined value such that an output impedance of the filter at the predetermined value is set to be different from that of a characteristic impedance of the filter so that signals flow from the input terminal of the amplifying element to the output terminal of the matching input circuit, an insertion loss of the filter and matching input circuit satisfies a condition according to a formula L i <L f +N m −10 Log(1−|γ s | 2 ) where L f (dB) represents an insertion loss of the filter in a case that both of the input and output impedances of the filter are set to be the characteristic impedance of the filter, L i (dB) represents an insertion loss of a circuit consisting of the matching input circuit and the filter, and N m (dB) represents a degradation amount of a noise figure of the matching input circuit.