Predistortion design of active filters to compensate for finite gain-bandwidth

Abstract

The effects of finite operational amplifier gain-bandwidth have only been considered relatively recently. Previous work centred around calculation of the shift in polo positions—or, equivalently, the ω0 and Q—due to known amplifier characteristics. The presumption is that the ideal design values are known. This paper takes the inverse approach. Assuming that the desired values of ω0 and Q are known, along with the operational amplifier characteristics, it presents a procedure for deriving the ideal values of ω0 and Q which will result in a shift to the design values. The method is, therefore, one of pro-distortion. The technique involves polynomial coefficient matching and the solution of a set of non-linear equations. The technique is developed for both single and multiple amplifier circuits, and a number of examples of each are presented. The paper concludes with experimental results proving the efficacy of the method.