Patent ID: 6912377

Claim:
A leak power ratio detection circuit for detecting a leak power to an adjacent channel of a radio frequency signal produced by a transmission circuit including at least power amplifier means for power amplification of the radio frequency signal, the leak power ratio detection circuit comprising: squaring means for squaring the radio frequency signal produced by the transmission circuit and producing a low-frequency component; a first filter for extracting a spectrum component corresponding to a desired channel, from that portion of the low-frequency component of the squared result obtained by the squaring means, which occurs with a center thereof being present near a DC (Direct Current); a second filter for extracting, from the squared result of the squaring means, a spectrum component corresponding to spectrum spreading due to a distortion in the transmission circuit; and leak power ratio detection means for detecting a ratio of the leak power to the adjacent channel of the radio frequency signal, on the basis of a level of the spectrum component extracted by the first filter and a level of the spectrum component extracted by the second filter.