Wide Band Tunable Filter Design Implemented in CMOS

Abstract

Generation of filters using operational transconductance amplifiers and capacitors (OTA-C) has become more and more popular. A simple yet effective method of analytical synthesis is presented that makes use of ladder circuits, which are much more widely understood. Given the ladder circuit of a filter of any order, an equivalent OTA-C filter can be easily synthesized. The synthesis process is shown for both a low pass and a band pass filter. Higher order filters can easily be synthesized by extending the design process described. The design of the band pass filter is implemented in CMOS with a linearly tunable OTA to show the effect of non-ideal elements. The CMOS filter implementation is capable of linear center frequency tuning across three degrees of magnitude. Because of the wide band width tunability, this type of design lends itself to intelligent frequency scanning techniques. Such a system, to be used in military applications, is presented as an application of this filter design.