Enhancing low frequency operation of active-RC filters employing R-2R networks

Utilizing R-2R ladders in design of active-RC approach promotes IC implementation of low frequency filters and leads to high linear and low power design solution for biomedical applications. However, area of R-2R ladders limits low frequency operation of this approach to few tens of Hz. This range is sufficient for designing 60Hz powerline notch filter, but biomedical lowpass filers requires much lower pole frequencies. This paper investigates the use of other type of ladders (R-αR) in filter design. It shows that R-1R, R-0.5R and R-0.1R ladders provide better solution than the R-2R counterparts for designing low pass filters with ultra-low pole frequency. Simulation results are provided to support the presented theory.