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22nd April 2004, 11:15 AM  #31 
diyAudio Member

I think I'll get the picture now, using SPICE. The last element is a resistor which will be conveted into a capacitor. It's OK to have a cap as load up to a finite frequency. Highpass fillter has a cap to "unlimited frequency => unrealistic current demands.
I'll guess that it's true that highpass filters can't be made by FDNR. In theory it will but not in real life.
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26th April 2004, 04:46 PM  #32  
diyAudio Member

Quote:
http://www.kemt.fei.tuke.sk/Predmety...ialy/ch029.pdf it's in part 29.3 of the article: 

27th April 2004, 01:06 PM  #33 
diyAudio Member

FDNR's are impossible to use a highpass filter but I can use the same style simulated inductor instead.
jackinnj, please note that your example is a simple negative resistance, not frequency dependent.
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27th April 2004, 01:27 PM  #34 
diyAudio Member

Per  no, the bottom figure is reactive.

27th April 2004, 01:34 PM  #35 
diyAudio Member

Yes, as L, inductance. I know how a GIC inductance looks like, just use one cap.
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14th July 2005, 06:42 AM  #36 
diyAudio Member

Why not use a gyrator circuit to simulate an inductor?
I do that in my own active filter one The manual has all equations needed \Jens 
14th July 2005, 06:55 AM  #37 
diyAudio Member

I know about the gyrator circuit with one or two opamps but a GIC looks cooler. I have no idea if it has any hidden good properties.
Jens, how come you found this old thread? Searched for FDNR?
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14th July 2005, 07:07 AM  #38 
diyAudio Member

Nope,
I just clicked your link in the bottom of your post \Jens 
22nd October 2010, 02:42 PM  #39 
diyAudio Member
Join Date: Oct 2010

HP FDNR
I know this thread is old and dead. But in case anyone was curious you can get a FDNR HP using something like the attached image. If you want LP just switch all the R's and C's

19th February 2011, 04:42 PM  #40 
diyAudio Member
Join Date: Dec 2009

I started investigating FDNR's again.
I used a 1 opamp grounded FDNR on my crossover page, and also a 1 opamp grounded gyrator (inductor simulator). Oneendisgrounded oneopamp FDNR's and gyrators use 1 opamp instead of 2, which is very useful for shunt legs on filters; its downside is it has a parasitic shunt R (in the case of the FDNR, series R in the case of the gyrator), which, with careful design, can be rendered insignificant. I used it to great effect, reducing my opamp count, over the 2 opamp gyrator/FDNR, and it is far less sensitive to component tolerance than the biquad type of zeropair implementation (according to Spice Monte Carlo analysis). With 2 opamps I achieved a 4th order elliptic filter (4 poles, 2 imaginary zero pairs). By configuring the opamp as a unity gain follower, open loop gain isn't that much of an issue, depending on the exact topology (e.g. if the impedance you need doesn't need to go very high); what you have to watch out for is the load presented to the opamp and the opamp input impedance (you usually need FET input opamps). The effect of open loop gain is apparent if you simulate gain = 0.99 (which is with open loop gain = 40 dB). (Ditto for effect of input impedance, on circuit's required max impedance). I wrote the page back in 2000: Jason Cuadra: Elliptic Crossovers Scroll to the bottom. Last edited by jasoncsbb; 19th February 2011 at 04:50 PM. 
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