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Analog filter - zero and transmission zero

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edafisher

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transmission zero

Hi all,
for analog filter, what does transmission zero mean? and what is difference between zero and transmission zero?
Thanks!
 

Re: transmission zero

Unless stated otherwise, zero means transmission zero. With other modifiers it can mean impedance zero (short circuit to ground at a particular frequency).
 

Re: transmission zero

flatulent said:
Unless stated otherwise, zero means transmission zero. With other modifiers it can mean impedance zero (short circuit to ground at a particular frequency).
Click to expand...

Sorry, I don´t think so.

1.) "Transmission zero" means that there is a real zero with ideally zero volts at the output - for example like a notch or a low pass with Chebyshev/invers approximation.

2.) "Zero" means (in most cases, if not stated otherwise) that there is a complex zero - like in allpass cicuits. As a consequence the output of the filter goes NOT down to zero volts.

Added after 47 minutes:

Supplement for clarification:
By using the phrase "zero" always a zero of the transfer function is ment.
 

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    edafisher

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Re: transmission zero

as I know

Transmission zero is the zero placed in the "stopband" of filter

it can improve the selectivity at the expense of stopband attenuation
 
Re: transmission zero

LvW said:
flatulent said:
Unless stated otherwise, zero means transmission zero. With other modifiers it can mean impedance zero (short circuit to ground at a particular frequency).
Click to expand...

Sorry, I don´t think so.

1.) "Transmission zero" means that there is a real zero with ideally zero volts at the output - for example like a notch or a low pass with Chebyshev/invers approximation.

2.) "Zero" means (in most cases, if not stated otherwise) that there is a complex zero - like in allpass cicuits. As a consequence the output of the filter goes NOT down to zero volts.

Added after 47 minutes:

Supplement for clarification:
By using the phrase "zero" always a zero of the transfer function is ment.
Click to expand...

i agree with you more, to make it clearer:

in case 1 you mean the zeros in jw axis, thus we get infinite attenuation.
in case 2 you mean the zeros those are NOT in jw axis, we get finite attenuation.
this is because the zeros of H(s) are zeros of H(jw) only when they are in jw axis (s=jw).

so i think when talking about "transmission zero", usually it means case 1, namely the zeros in jw axis.
 

Re: transmission zero

Hi edafisher,

thank you for clarification as I have expressed myself a bit misleading in my reply to flatulent.
When I say "real zero", of course I don´t mean a zero on the real axis but instead a "realistic" zero of the output voltage at a certain frequency. And this means as correctly stated by you: In the complex plane the zero is placed on the Im-axis.
Thak you, regards. LvW
 

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