Summary: A direct conversion receiver IC including an on-chip balun, an I/Q mixer, a variable gain amplifier and a 90 phase-shifter is fabricated in a Bi-CMOS technology with 15 GHz transition frequency (fT). This paper demonstrates that cascaded connection of an on-chip balun and a double balanced mixer as the I/Q mixer is effective to achieve a low DC offset and a low second-order distortion, on the basis of both careful examination of the mixer behavior and measurement. Input-referred DC offset voltage of less than 300 µV and spurious free dynamic range (SFDR) of over 67 dB are obtained by measurement. The IC consumes 52 mA from 2.7 V power supply voltage. The die size is 3 mm 3 mm.