How to create an LC parametric attenuation circuit in simulink.

The terminals are LC only, L=0.1H and C=0.25F with an initial voltage of 1V. The variable capacitor has an initial capacitance of 0.25F and is increased by 0.25F each time the voltage takes an extreme value. The judgment of the extreme value is made by the derivative block, which outputs an impulse signal when hitcrossing becomes 0. Q=CV, and since Q is conserved, C is increased so that V is attenuated.The circuit I am currently working on is as follows, but it does not work well.

The ideal graph is as follows.

[光希]

Circuit has been updated. Voltage waveform is not attenuated.

subsystem(add 0.25F)

Answer 1

[Vinay]

Hi @光希,

The LC attenuator here uses a variable capacitor so the concept of steady state capacitance which states Q = CV is applicable only when capacitance remains constant regardless of voltage applied.

In this case a differential capacitance is applied and defined as gradient of charge voltage curve and equation is modelled as i=dCdtv+Cdvdt.

The issue can be resolved by changing the equation parameter of the capacitor to differential case.

Kindly refer to the below documentation of “variable capacitor” for more details:

https://www.mathworks.com/help/sps/ref/variablecapacitor.html

I hope this helps!