Active-filter pole displacement due to nonideal operational amplifiers

The effect of nonideal operational-amplifier output impedance on active-filter pole displacement or pole variation, respectively, is discussed and compared with the effects of finite amplifier gain and gainbandwidth product. The analysis shows that the pole variation is mainly dependent on three factors: the gain-sensitivity product, the pole frequency rated with the gain-bandwidth product, and the amplifier output resistance RA as compared to the network impedance level R¿¿. The influence of the amplifier output impedance on the total pole shift can be varied, within some practical and technological limits, by the choice of the impedance level R¿¿. The results have been verified experimentally.