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This paper presents the design and analysis of a large-gain-range wide-bandwidth VGA in 0.13 μm CMOS for 6GHz RF communication system. The principles of AGC and the role of VGA in it are discussed; the main structures of CMOS VGA are systematically studied, as well as the realization of exponential function in CMOS process. A structure based on cascode amplifier is adopted as variable gain unit for the designed VGA, which can achieve gain controllable and exponential characteristic at the same time; the active inductor peaking circuit is applied to extend the bandwidth; the dual feedback DC-offset cancellation circuits are used to reduce the overall DC-offset. The post simulation results show that the dB-linear gain range is 70dB (-4dB~66dB); the 3dB bandwidth is 600MHz; the power consumption is about 9.8mW from 1.2V power supply.