Title:Synthesis for Butterworth Filter Using Compact VDTA Based on Sallen- Key Topology
VOLUME: 13 ISSUE: 5
Author(s):Yong-An Li*
Affiliation:School of Information Engineering, Shaanxi Institute of International Trade & Commerce, Xi’an
Keywords:Current-mode circuit, sallen-Key topology, Butterworth filter, VDTA, adjoint network theorem, nodal admittance
matrix expansion.
Abstract:
Background: The original filter including grounded or virtual ground capacitors can be
synthesized by using the NAM expansion. However, so far the filters including floating capacitor,
such as Sallen-Key filter, have not been synthesized by means of the NAM expansion. This is a
problem to be researched further.
Methods: By using the adjoint network theory, the Sallen-Key filter including floating capacitor
first is turned into a current-mode one, which includes a grounded capacitor and a virtual ground
capacitor. Then the node admittance matrix, after derived, is extended by using NAM expansion.
Results: At last, one VDTA Sallen-Key filter is received. It employs single compact VDTA and two
grounded capacitors.
Conclusion: A Butterworth VDTA second-order frequency filter based on Sallen-Key topology
with fo = 100kHz, HLP = -HBP=1, is designed.