Issue link: https://iconnect007.uberflip.com/i/1391285
86 DESIGN007 MAGAZINE I JULY 2021 at about the same frequency where the source impedance has the peaking. We can also simulate the input and output impedance of the full filter with its actual ter- minations. As shown in Figure 6, we can simu- late the output impedance of the filter with the source-side impedance connected. In the reverse direction, the input imped- ance is simulated with the assumption that the load has very high impedance and therefore we can leave the output of the filter open. On the input side of the filter, we drive the series inductive element without a shunt capacitor included. is is an acceptable approximation for unidirectional filters when the impedance of the source rail is much lower than the input impedance of our filter. When we need to work with multi-stage and/or bi-directional filters, where the driving source impedance is not much lower than the input impedance of our filter, we need to identify and include, both at the input and at the output, the capacitors that belong to our filter circuit. e input and output impedance curves of the full filter are shown in Figure 7. e input impedance curve compares to the blue line in Figure 5 with the difference that now we have a 2.7 uH inductance in series. is creates an Figure 5: Impedance magnitude of the source rail, the inductor, and the output capacitor of the filter. Because we used a 1A AC source, the voltages at these nodes directly represent impedance. Figure 6: Simulating the full input and output impedance of the filter.