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Ideal low pass Filter with linear phase and with square S21

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jayce3390

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Ideal low pass Filter

Hi,

I need to use an ideal filter in ADS circuit simulation. But the component palette doesn t provide ideal filter, only Chebychev, Butterworth...

Is it possible to create ideal filter with linear phase and with square S21?
With SDD?is it a good way?

thank you
 

Re: Ideal low pass Filter

No. The closer you get to a rectangular response, the worse the phase and time delay distortion. This is part of the physics of a filter that is described by a mathematical polynomial.
 

    J

    jayce3390

    Points: 2
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Re: Ideal low pass Filter

thanks a lot.

Yes kspalla, you suggest me to try in ADS , but how can I set an ideal filter in ADS? You are thinking about SDD component or a ideal filter component exists in ADS?

If yes I don't find it.:|

flatulent, if phase shows 2pi shift, can we consider this linear?

 

Re: Ideal low pass Filter

Is it possible to create ideal filter with linear phase and with square S21?
Click to expand...

Almost yes, but it's a bit of a cheat. Go to the 'Filters-Bandpass' palette and select
a SAW filter. This is of the high-loss linear phase type.. but ADS lets you set the
loss to whatever you like. Set the passband such that the lower edge of the filter
is at 0Hz or lower (since you probably don't care about negative frequencies). Set
the group delay to whatever you need. Set BWstop (rejection) close to the
passband for a near square S21.

In reality this filter is impossible as a SAW filter, but digitising and implementing
as an FIR filter might be possible(not my speciality!) depending upon the filter
cut-off frequency.

Hope that helps.

Martin
 

    J

    jayce3390

    Points: 2
    Helpful Answer Positive Rating
Re: Ideal low pass Filter

Ok thank you, indeed SAW filter in ADS provides linear phase if parameter is let to default according to the help, but after simulation the phase is not linear...

if anyone could give me link or documentation to implement low pass filter with equations I will apreciate.

thanks in advance
 

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