High-frequency fully differential filter using operational amplifiers without common-mode feedback

A technique for realizing a fully differential filter using an operational amplifier (op amp) without common-mode feedback (CMFB) is presented. This technique results in a smaller area, a reduced power dissipation, and an improved speed and dynamic range of the filter. Experimental results of a biquad switched-capacitor bandpass filter with a center frequency of 3.5 MHz and a Q of 24 are presented. The op amp has an open-loop unity-gain bandwidth of 230 MHz, a phase margin greater than 50 degrees , and a DC gain of 76 dB. The prototype filter occupies only 0.26 mm/sup 2/ and dissipates 6 mW with a 5-V supply.>