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.
