Synthesis for Current-Mode Sallen-Key Filter Using VDTAs

In this work, an original Sallen-Key second-order low-pass filter is first turned into a current-mode one by means of the adjoint network theorem. Two nodal admittance matrices（NAM） of the filter are then educed. Furthermore, these two matrices are expanded through NAM expansion approach, generating one current-mode Sallen-Key filter, which uses two compact voltage differential trans-conductance amplifiers（VDTAs） and two grounded capacitors, implements not only one low-pass transfer function but two band-pass transfer functions, and provides the non-interrelated control between the natural frequency and quality factor. As an example of the synthesized filter, a second-order VDTA filter with f;=1 MHz, Q=1, H;=-H;=H;=1 is designed. The used synthesis approach has been confirmed with the help of circuit and computer analysis.