Patent ID: 7171185

Claim:
An AGC circuit in a direct conversion receiver for multiplying a received high-frequency signal by a local signal with a frequency substantially the same as that of the high-frequency signal to directly convert into a baseband signal, amplifying the baseband signal using a baseband variable gain amplifying circuit having a variable gain amplifier, low-pass filter and a high-pass filter for cutting off a DC component as structural elements, and performing A/D conversion and demodulation on the resultant, the AGC circuit comprising: a power measuring section that measures reception power based on a signal subjected to A/D conversion; a gain calculating section that calculates a gain of the variable gain amplifier using information of a difference between measured reception power and a target convergence value; a gain control section that controls the gain of the variable gain amplifier based on the calculated gain; a filter control section that has a function of switching a cut-off frequency of the high-pass filter between at least high-and-low two frequencies; and a gain variation amount detecting section that reports to the filter control section upon detecting that the gain of the variable gain amplifier varies by an amount equal to or greater than a predetermined amount as a result of control by the gain control section, wherein: the filter control section switches the cut-off frequency of the high-pass filter to a high frequency upon receiving the report from the gain variation amount detecting section; and the gain calculating section and the gain control section perform at least one of processing for increasing a range of gain variation per update and processing for shortening a period of the update during a period of time the cut-off frequency of the high-pass filter is switched to the high frequency.