A practical design for insensitive RC-active filters

Abstract

A systematic RC -active network synthesis procedure for the realization of second-order transfer functions is proposed. The realization employs three operational amplifiers and no isolation amplifiers are necessary. The sensitivity of the resulting networks to passive element variations has been found to be low. The sensitivity to variations in the active elements has been made very low. A design is given in which tuning can be achieved by trimming only resistors. The design is particularly attractive for high- Q realizations. The stability properties and the influence of the finite bandwidth of the amplifiers are examined. The proposed realization has been compared with those of Kerwin, Huelsman, and Newcomb, of Tarmi and Ghausi, and of Thomas, and found to offer several attractive features as compared to these realizations. The design procedure was used to obtain a sixth-order elliptic bandpass filter. Experimental results show close agreement between theory and practice. Further, these results indicate that these realizations are insensitive to temperature and power supply variations.