:<math> \frac{v_{out}}{v_{in}} = \frac{ \sum_{m=0}^{M} b_m s^m }{ s^N + \sum_{n=0}^{N-1} a_n s^n } = \frac{ \sum_{m=0}^{M} b_m s^{-(N-m)} }{ 1 + \sum_{n=0}^{N-1} a_n s^{-(N-n)} } </math>
In the above equation, the transfer function s<sup>-1</sup> can indeed be realized using the analog integrator macromodel that was discussed earlier. Using a cascade of integrators one can realize the general rational transfer function as shown in the figure below:
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[[RF.Spice]]'s "Generalized Analog Filter Block" does this realization automatically for any arbitrary filter order (or highest degree of the s-variable). You enter the denominator and numerator coefficients as arrays of real numbers. The figure below shows the property dialog of this black-box macromodel.
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<td> [[Image:Integ4.png|thumb|560px|The property dialog of the generalized analog filter block.]] </td>
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