Fabio Gonzalez suggested: > For reference: > Analog Devices AN-281 "Passive and Active Analog Filtering" - > Frequency Dependent Negative Resistor (FDNR) - pag.4 There's also a very nice article about nics in combination with gyrator based filters here.. http://www.e-insite.net/ednmag/archives/1994/072194/15di1.htm