This paper presents a wide intermediate-frequency (IF) bandwidth down-conversion double-balanced Gilbert-cell mixer design in a 0.13-μm CMOS process. The load stage of the mixer is implemented by an LC tank with switched capacitors to complete three selectable sub-bands to cover the desired wide IF band. Both the RF and LO ports are integrated with Marchand baluns for single-phase input consideration. The mixer converts millimeter-wave ISM band of 57.3-59.2 GHz down to the first UWB sub-band of 3.3-5.2 GHz (total 1.9 GHz bandwidth) with a fixed local frequency of 54 GHz. The measured conversion gain is better than -3 dB over the desired IF bandwidth. The levels of input 1-dB compression point (IP1dB) are -3, -3, and -1 dBm correspond to the center frequencies of 3.8, 4.2, and 4.6 GHz, respectively. The LO-to-RF isolation and LO-to-IF isolation are better than 43 dB and 35 dB, respectively.