Fundamental frequency limitations in current-mode Sallen-Key filters

Author

Schmid, Hunspeter ; Moschytz, George S.

Author_Institution

Inst. for Signal & Inf. Process., Fed. Inst. of Technol., Zurich, Switzerland

Volume

1

fYear

1998

Firstpage

57

Abstract

Single-amplifier filter biquads and especially Sallen-Key filters are widely used to build higher-order filter cascades. This paper investigates high-frequency current amplifier non-idealities and their effects on all-pole Sallen-Key filter biquads. It is shown that a non-ideal current amplifier input causes parasitic zeros in the filter transfer function, and thus imposes fundamental limitations on the realisable pole frequency. Design equations are given, providing compensation for their amplifier´s port impedances and its phase lag, by predistortion of the component values. It is also shown how design specifications for a current-amplifier can be derived from the filter specification, minimising the amplifier´s power dissipation. Finally, a video-frequency lowpass filter is discussed

Keywords

biquadratic filters; cascade networks; compensation; low-pass filters; poles and zeros; transfer functions; amplifier nonidealities; compensation; current-mode Sallen-Key filters; design specifications; filter specification; filter transfer function; frequency limitations; higher-order filter cascades; parasitic zeros; phase lag; port impedances; power dissipation; predistortion; realisable pole frequency; single-amplifier filter biquads; video-frequency lowpass filter; Admittance; Band pass filters; Frequency; Impedance; Information filtering; Information filters; Negative feedback; Output feedback; Transfer functions; Voltage;

fLanguage

English

Publisher

ieee

Conference_Titel

Circuits and Systems, 1998. ISCAS '98. Proceedings of the 1998 IEEE International Symposium on

Conference_Location

Monterey, CA

Print_ISBN

0-7803-4455-3

Type

conf

DOI

10.1109/ISCAS.1998.704174

Filename

704174