Title :
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
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;
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
DOI :
10.1109/ISCAS.1998.704174
