QLPFB models represent lumped-element Butterworth quasi-lowpass filters. They offer simplicity and a compromise between high selectivity and flat group delay. The insertion loss is maximally flat at the passband's geometric center and the upper stopband attenuation increases monotonically.
|HN||Half the number of reactances.||3|
|FL||Lower frequency edge of passband (when Qu is infinite).||Frequency||0.5 GHz|
|FH||Upper frequency edge of passband (when Qu is infinite).||Frequency||1.5 GHz|
|*AP||Maximum passband attenuation (when Qu is infinite).||DB||3.0103 dB|
|*RS||Source resistance.||Resistance||50 ohm|
|*RL||Load resistance||Resistance||50 ohm|
|*QU||Uniform unloaded Q reactive element in the filter||1e12|
* indicates a secondary parameter
0 < HN < 29
0 < FL
0 < FH
0 < AP Recommend AP greater than or equal to 0.001 dB.
0 < RS
0 < RL
0 < QU. Recommend QU less than or equal to 1e12.
The model is implemented as a short-circuit admittance matrix, whose equivalent transfer function squared magnitude is that of a Butterworth filter:
and a lowpass-to-quasi-lowpass frequency transformation has been applied:
_FREQ is the variable containing the project frequency, and the admittances are:
This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.
Note that this model behaves as if it has ideal impedance transformers at its ports, so there is no attenuation due to mismatched source and load impedances. The model expects that the source impedance will equal RS and that the load impedance will equal RL, but RS need not have any special relationship to RL for ideal transmission (as would normally be the case).
 Rolf Schaumann, Mohammed S. Ghausi, and Kenneth R. Laker, Design of Analog Filters: Passive, Active RC, and Switched Capacitor, (Prentice-Hall, 1990), pp. 40-44.
 Louis Weinberg, Network Analysis and Synthesis, (Robert E. Krieger Publishing, 1975), pp. 493-498.
 Adel S. Sedra and Peter O. Brackett, Filter Theory and Design: Active and Passive, (Matrix Publishers, 1978), pp. 105-111.
 Max W. Medley, Jr., Microwave and RF Circuits: Analysis, Synthesis and Design, (Artech House, 1993), pp. 312-317.