A CMOS direct sampling mixer using Switched Capacitor Filter technique for software-defined radio

This paper proposes a novel direct sampling mixer (DSM) using switched capacitor filter (SCF) for multi-band receivers. The proposed DSM has a higher gain, more flexibility and lower flicker noise than that of conventional circuits. The mixer for digital terrestrial television (ISDB-T) 1-segment was fabricated in a 0.18 mum CMOS process, and measured results are presented for a sampling frequency of 800 MHz. The experimental results exhibit 430 kHz signal bandwith with 27.3 dB attenuation of adjacent interferer assuming at 3 MHz offset.