See updated 2019 version of this article here.
In Filter Wizard #12 (Filter Design using the Million Monkeys Method) I made myself extra work by promising more detail on several filter design and network theory issues that I rushed through at the time in my quest for a fast-paced, interesting article. So, here’s the first of those “deep dives”: why did I want to set my source and load resistances to the same value?
The filter topology used in the article is known as a doubly-terminated LC ladder filter. The inductors and capacitors form a network with two ‘ports’ – places where signals can enter and leave the network. In our filter, the input port is fed from a source that has a particular resistance value (that you usually can’t change), and the output port is connected to – “loaded by” – another resistor (that’s often under your control).
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About the author
Kendall Castor-Perry is a Principal Architect at Cypress Semiconductor, 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.