Biquadratic SC filters with small GB effects

Abstract

The effects of proper switch phasing in SC filters to yield low gain-bandwidth (GB) product dependence is discussed. A figure of merit for comparing GB effects in SC networks based upon the topology dependent effective GB matrices has been introduced. Motivated by this consideration, two general biquadratic switched-capacitor filter structures are presented. These circuits are stray-insensitive, have small <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\omega_{0}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> sensitivities, and are easy to apply. A significant feature of these biquads is their reduced dependence on the operational amplifier GB product. Filter center frequencies up to the 50-kHz range are feasible for op amps with typical values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GB/2 \pi = 10^{6}</tex> Hz, making these circuits attractive for high-frequency applications. The advantages of the proposed structures are demonstrated by an example. Results enabling the designer to determine the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\omega_{0}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> deviations for different values of GB are presented. A comparison of theoretical and experimental results shows good agreement.