Elliptic Lowpass Filter  (LPF_ELLIPTIC)

This element is used to provide filtering in the RF path. This system symbol is available on the System toolbar.

 

Models and Symbols

 

Name

Model

LPF_ELLIPTIC

Alternate Models

LPF_ELLIPTIC_C

Schematic Symbol

LPF

Alternate Schematic Symbols

None

NOTE: The alternate model "..._C" is a circuit model created from a synthesis process with real components. The circuit is not visible to the user. Simulation time for the circuit models is generally longer since there are more components.

 

Model Parameters

Parameter

Description

Units

Default Value

IL

Insertion Loss

dB

0.01

N

Filter Order

none

3

Fpass

Passband Edge Frequency

MHz

200

Apass

Attenuation at passband

dB

3.01

Amax

Max Attenuation in stopband

dB

100

Z1

Reference Impedance Port 1

Ohm

50

Z2

Reference Impedance Port 2

Ohm

50

TYPE

Input Stopband Impedance (0 = Short,  1 = Open)

none

1

 

The Elliptic filter characteristic exhibits ripple in the passband and generated by poles and zeros. This results in a cutoff which is sharper than most other filters. The insertion loss only affects the forward (S21) and backward (S12) transmission, but not the reflection coefficients (S11,S22). The input impedance in the stopband only affects the phase of the reflection coefficients. The value for the attenuation at the passband edge (Apass) is the ripple value. For filters of even order, the gain at dc is less than unity to avoid gains greater than unity in the passband. For additional details on filter types see the FILTER Synthesis Manual.

Note: The insertion loss must be greater or equal to zero. The filter order must be an integer greater or equal to 2. The frequency of the passband edge must be positive. The stopband attenuation must be greater than the ripple.

DC Block - DC will only be blocked by the amount of attenuation at 0 Hz.

Maximum Attenuation in stopband - The maximum attenuation in the stopband is modelled with a resistor between the input and output port of the filter.  An equation is used to determine the value of the resistor from the given attenuation.  This parallel resistor will only be effective when the filter stopband impedance TYPE is set to open. For even filter orders the impedance looking into one port is high and the other low so the maximum attenuation in the stopband has no effect.