Communication semiconductor integrated circuit, radio communication system, and adjustment method of gain and offset

Abstract

A D.C. offset canceling technique and a gain adjusting technique permitting completion of correction of D.C. offsets and gain adjustment of amplifiers for amplifying reception signals in a relatively short period of time in a radio communication system, such as a wireless LAN, are to be provided. A communication semiconductor integrated circuit (high frequency IC) has a plurality each of low-pass filters and variable gain amplifiers which are alternately connected in multiple stages, and high gain amplifier circuits for amplifying reception signals to a predetermined amplitude level while eliminating unnecessary waves. Offset cancellation values are generated by detecting in advance D.C. offsets of amplifiers for amplifying reception signals according to a set gain, and stored into a memory, and read out of the memory to cancel the D.C. offsets of the amplifiers at the time of starting reception and altering the gain. Gain setting in a high gain amplifying section for amplifying reception signals is accomplished in two steps, rough setting and precise setting.