In the process of designing a lumped element filter, the circuit layout that is usually used to realize the filter is known as the “ladder network”. Why ladder? Simply saying, because the layout looks like a ladder. The picture below shows a ladder network that is consisting of only resistors. In a lumped element lowpass filter, the ladder network layout will consist of inductors connected in series and capacitors connected in shunt.
However, we may want to eliminate the series or shunt elements of the circuit in some cases. When is that needed? Usually this is needed when wanting to convert the circuit into its distributed equivalent. For example, when realizing an interdigital design, the stubs are all in shunt configuration. Therefore in the ladder network, configuring it to be fully shunt layout would make the Richard’s transformation to the distributed equivalent to be much easier.
So, this is when we need a component called the Inverter. When placing an inverter component, it allow us to convert the next element to the opposite configuration. For example, by placing an inverter before a supposingly shunt element, we can then convert the shunt component into a series component.
Using Inverter in EDS
In this week demo video, we demonstrate how to use an inverter in our EDS HF software. In this short video, you will see that the response of the lowpass filter constructed is the same in both the ladder network and inverter layout. Be sure to check out more theoretical write-up about the usage of Inverter in the PDF attached.