Current-mode elliptic filter design based on symmetrical current switching

This paper describes a current-mode elliptic filter structure based on dual -output OTAs and grounded capacitors. The filter is capable of producing bo th lowpass and highpass notch responses without changing the filter structu re. This is achieved using a symmetrical current switching technique based on two switches controlled with a 2-bit digital word. The proposed filter s tructure forms a basic second-order building block in the design of high-or der elliptic filters with tuneable frequency response. To confirm the theor etical analysis, simulated and measured results of fourth-order elliptic lo wpass and highpass filters with tuneable bandwidth in the range of 0.65 MHz to 1.3 MHz are included. Finally, detailed analysis of the OTAs non-ideal parameters on the filter performance is presented and an example is given.