Accurate CMOS current-mode-filters for high frequencies and low power consumption

Analog signal processing in many applications requires low-noise, low-power filters that are little sensitive to element value variations. To meet such requirements the leapfrog approach can be applied to synthesize active filters from passive LC filter prototypes based on state equations. These achieve high accuracy in the presence of the typically large element value variations in IC fabrication processes. To enable low noise and low power operation in spite of high signal frequencies a careful choice of the filter synthesis and building blocks is indespensable. In this communication we compare filters realized in operational amplifier technique with current-mode filters in respect of their suitability for implementation of a fourth order bandpass filter used for IF processing in heterodyne receivers. Also, we determine the component values necessary for implementation of the current mode circuit in order to compute the input referred noise of the resulting current-mode filter using a simplified transconductor model.