When using a Transfer Function Block, and you enter in the polynomial coefficients for a simple RC Passive Low-Pass Circuit, and perform an AC analysis side-by-side to its circuit equivalent, it works great. The 2 frequency response waveforms are identical. However, when you add another RC Low-Pass section in cascade with the 1st one, making it a 2-pole RC Passive Low-Pass Circuit, and you put its polynomial coefficients into the transfer function block the results of the AC Frequency Response is not identical to its 2-pole circuit equivalent. I double checked my math to make sure my transfer function math was correct. Since 2 transfer functions are in cascade, the transfer function from the 1st RC stage is multiplied times the transfer function of the 2nd RC stage, and the result is the overall transfer function. I even went as far as creating 2 transfer function blocks, each of them, with a single RC transfer function and connecting them in a cascade fashion. The results were the same....the trasnfer function block(s) do not resemble their circuit equivalent models for a >=2pole Passive RC Low-Pass filter.
