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What are active inductors?

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Junior Member level 3
Feb 12, 2006
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I was wondering if someone can tell me what active inductors are, and how they are made in cmos. THANX in ADVANCED

Re: Active Inductors

Are you talking about a GIC (general impedance converter)? These have been around a long time -- take a look at Active Filter Design by VanValkenburg. These are basically two-terminal circuits made from opamps, resistors and a capacitor. When you take a look into the two terminals, you see an i-v (current-voltage) characteristics that mimic and inductor. For example, if you apply a sinusoidal voltage and measure the sinusoidal current going into the device, you see that the voltage leads the current by 90 degrees -- which is what you would expect from an inductor. However, as I already said, the circuit does not contain any inductors. The value of the inductance depends on the capacitors and resistors used in the circuit.

So I think what you are looking for is a CMOS implementation of this. Or maybe there are other techniques. But I know for a fact that GICs were implemented in many active filter designs.

Try googling "GIC general impedance converter" or taking a look at the reference from above. I think the original version of the book was published in 1982.

Best regards,

Re: Active Inductors


It is true that there is so much papers and presented circuits deploying GIC, but be carefull for chosing topology. Because some nonideality in OpAmps by some presented schematics can destroy your transfer function.
You schould carefully simulate offset issue and frequency characteristic.


Re: Active Inductors

Try looking this book: Design of Active RC circuits
Author: Leonard T. Bruton (this book is out of print though)
Presents extensively about Immitance Converters.
Also, look on IEEE Xplore for R. Senani. He has been working with these for a long time.

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