Note: Do not save the schematics after usage because they may be used in later examples.
Note: Opening the schematics from the links is best done with a Click+Drag over an existing opened instance of LTspice.
Setting any of the following parameters to zero allows for various optimizations. There can only be one null parameter at a time.
For convenience, some schematics already have .step commands commented out.
  1. Following the first method, suppose a minimum order for a -3dB@1rad and -60dB@2rad LP is needed for unity source/load. Choosing Butterworth_LC, the configuration looks like this:
  2. For the second method and using the same values, BWs can be 1k or even higher, as long as the conditions are satisfied. The same goes for As: it can even be null because N dictates the attenuation. More concrete:
    The.TRAN analysis shows the Nyquist impulse response (and how the impulse is affected by the input).
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  1. Chebyshev_LC with -3dB@100MHz, 1dB ripple, -50dB@95MHz, 50Ω input, 75Ω output:
    The resulting order is even so the response will be distorted with the current input/output impedance settings. This could be resolved by either increasing the order or by increasing Zout to minimum tanh(asinh(1/sqrt(10**0.1-1))/4)**2 (for Zin≤Zout) or its reverse (for Zin<Zout).

  2. The same example, adapted and with increased order:
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  1. Butterworth_LC, -3dB@[100Hz,10kHz], -60dB@[50Hz,20kHz], Zin=Zout=8Ω. Some calculations need to be done first:
  2. The same, adapted:
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  1. Chebyshev_LC, -3dB@[300Hz,3400Hz], -60dB@[425Hz,2400Hz], 0.1dB ripple, Zin=Zout=600Ω. After the same calculations as above:
  2. The resulting order would be odd (18/2=9), so the equal terminating impedances can be used.

  3. The same, N specified:
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A LP Butterworth_LC will be considered for all three cases. The current source in the schematic must not be left floating.
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Since they can only be used in transient simulations, viewing them is done by switching over to the .TRAN card. For this case, using the same low-pass example, setting test=1 will enable pin 0.2 (the net named elements) and sim=50 will ensure that all the discrete values will have equal shares and will span over the entire time scale.
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