Blog The Filter Wizard Remastered

The ins and outs of generalized impedance converters

See the updated 2019 complete article here.

Filter Wizard #16,“ Bruton Charisma”, showed how we could apply an arbitrary scaling factor to each impedance in an LRC filter network, to create another network that has the same transfer function but is assembled from a different ‘set’ of components, with familiar Rs and Cs and also a new guy, the D-element. But we didn’t get as far as figuring out how we would actually make up such a thing, a ‘component’ whose impedance equals -1/(Dw2 ).

Such a component doesn’t exist in passive form. How might we systematically develop a way of creating such a circuit configuration? Do we have to randomly juggle around a bunch of Rs, Cs and op-amps until we encounter a circuit that has an impedance formula that does the job? Well, that’s another Million Monkeys project in its own right; interesting work has been done on topology development by guesswork {cough} sorry, I mean optimization. The subject of a future article, perhaps, but not disciplined enough for my purpose here.

Here we’ll address the central problem straight on. We’ve shown that we can
conceptually create a new element by multiplying a component’s value by a factor K that’s a function of frequency. Can we now practically realize such an element by attaching our initial component to some kind of ‘impedance scaler’?

This article explores what can be done, and how, to scale filters and realize impedance conversion with a different approach. To read the article, To read the article, which originally appeared in EE Times-Europe (Analog) , click here .

About the author
Kendall Castor-Perry is a Principal Architect at Cypress Semiconductor Corp.,doing mixed-signal system analysis and design for the new PSoC platform. Kendall uses decades of experience in analog engineering, filtering and signal processing to capture signals across many domains, extract the information from them, and do something useful with it.


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