The delay in filters other than passive

[seyyah]

Filters

Passive filters have some drawbacks like delay. How about active filters? Can they filter fast enough. Also how about the digital filters. I don't know much about them. Can they be used instead of analog filters. For example can we use FIR or IIR filters instead of an analog low pass filter? If so is it possible to find ready modules or codes for digital filters just for take and use for now. Because i don't have much time for now to fully concentrate on digital filters but if i can first learn how they works or use them (may be in a simple case) i can learn them in time in detail. Also what are the differences between FIR and IIR. I think there are much more filters than these both but i hear more about these ones.

 

[moda]

Re: Filters

Passive filters have some drawbacks like delay. How about active filters? -
Answ- Thay have dalay as well- if you want to lern more - read this- **broken link removed**
You can find more on the WWW
find more info about Fir chip filter at TI GC2011

Moda

 

[seyyah]

Re: Filters

Good device but it is almost a ready module. If it wasn't so expensive it may be a good selection. May be cheaper ways or designs using standart opamps are more convenient.

 

[flatulent]

Re: Filters

The delay is inherent in the polynomial of the filter response and not in the passive or active method of implementing it. The FIR digital filter will have an average delay of half the delay line length.

If all you are interested in is the relative delay between two signal paths, you can put a delay line in one or the other to make the relative delay whatever you want.

 

[moda]

Re: Filters

What typ of filter do you need? What freq? LPF, HPF, BPF? You have at TI sw and help for opamp filters,
http://www-k.ext.ti.com/SRVS/CGI-BIN/WEBCGI.EXE/,/?St=258,E=0000000000000262856,K=8448,Sxi=15,Problem=obj(25887)

 

[seyyah]

Re: Filters

I usually need LPF. May be i can't design very well i don't know but i want to get faster responses. I plan to use them to get instantenous values of a signal or low frequency signals or dc which have harmonics on them. I'm trying simple passive filters but it is diffult to read the correct value faster enough. I usually make current, voltage or encoder readings. As an example to make the subject clear, i use a low pass filter to read an optical encoder data. I couldn't be able to find a way to read it perfectly. If i increase the cutting frequency it reads unwanted pulses (noise), if i decrease it then it misses the pulses. In a current reading, the reading must be much faster and i must read the instantenous value of the fundamental so i must filter the harmonics fast enough.
By the way ti's webpage has good info i think, i'll look at it, thanks.

 

[moda]

Re: Filters

Look at the Maxim LPF its the best I think for your application, I have used it in the past and you can configure it the way you want (digital/analog LPF)
MAX7422
Moda

 

[djalli]

Re: Filters

I usually need LPF. May be i can't design very well i don't know but i want to get faster responses. I plan to use them to get instantenous values of a signal or low frequency signals or dc which have harmonics on them. I'm trying simple passive filters but it is diffult to read the correct value faster enough

Theoretically and practically (depends how many nanoseconds is practical for you) you never will. i.e. it takes time for the electron to vibrate, it never happens instantaneously.

How fast you want it? Well, A trade-secret is "to buy expensive capacitors". Try tantalum in place of electrolytic ones.

 

[seyyah]

Re: Filters

2 us max i need. Can digital filters help in this situation for faster responses?

 

[djalli]

Filters

no, digital filters are slower then analog in such case ...

 

[moda]

Re: Filters

Read this -" Fast settling LPF" I hop that will help you more.
You can get 2uSec settling time.
https://focus.ti.com/lit/an/sboa011/sboa011.pdf

 

[seyyah]

Re: Filters

It seems that Texas has extensive knowledge base in their website as you refer them always . So it'll be good to search the manufacter's sites for basic knowledge or design tips or what products are available? Do they allow to download all of them in a package or do they give it in a cdrom etc?

 

[Borber]

Re: Filters

As a mater of fact, higher the filter order more delay it will produce. Lowest delay has first order filter and so on. Filter type does not change delay significantly but ringing is diferent. Lowest ringing has Gaussian and Bessel types and it rises if Butterworth, Chebyshev or Eliptic. This is valid for linear transfer functions and for passive or active design.

 

[moda]

Re: Filters

Yes, Thay do have extensive knowledge base,and you can download tip and triks not a package or cd, I know them prity good, it take some time to find what you need at Ti site.
Is it good design for you?

 

[seyyah]

Re: Filters

As a mater of fact, higher the filter order more delay it will produce. Lowest delay has first order filter and so on. Filter type does not change delay significantly but ringing is diferent. Lowest ringing has Gaussian and Bessel types and it rises if Butterworth, Chebyshev or Eliptic. This is valid for linear transfer functions and for passive or active design.

What's ringing?

Added after 7 minutes:

Yes, Thay do have extensive knowledge base,and you can download tip and triks not a package or cd, I know them prity good, it take some time to find what you need at Ti site.
Is it good design for you?

I must check them all. But i think i can find something useful at least, thanks.

 

[Borber]

Re: Filters

By ringing I meant overshoots in beginning of response to step pulse.

 

[seyyah]

Re: Filters

Ok understood the ringing. I think i must try to make the harmonics at a frequency as possible as high.