Hi,
Post#6 is totally confusing to me, because it mixes just a bunch if technical terms.
For example:
* 2nd order, 4th order, cascading...
It seems you try to use a 2nd order ... then add another 2nd order ... but ignore that cascading shifts the cutoff frequency
You mean to say that cascading two 2nd order filters with cutoff frequency = fc for each result in 4th order filter but with different fc ?
* MFB tecnology is mixed with biquad topology.
But MFB is an analog filter ... while a biquad is a digital filter (which can't be used as anti aliasing filter, for example)
* and other issues
biquad can be digital and can be analog, an example of the analog is the Two-Thomas filter, the latter one which I am comparing to MFB or Sallen-key or Gm-C filter
Klaus
You are a designer, so you decide - I am not going to decide for yourself, only gives answer for question ;-)I see you didn't cancel the option of the Gm-C filter completely as our friend Suta did.
7 orders of magnitude of tunability?You emphasized on a good point of Gm-C filter, that is tunability, since my task is to design tunable low pass filter with tunable fc vary from tens of hertz up to 5 MHz.
As long as your signal swing is higher than few mV it will not work. Linear pseudoresistor is challenging, and you will need to have a few of them matched together. People were trying this in past, but with no big success.If the main feature of the Gm-C filter is regarding the tunability, the MFB filter, for example, can also be tuned by using Mosfet-resistors and which can be tuned to by changing the gate voltage.
Thanks for clarifying this. I wonder why I never realized this terminology for analog filters.Biquad filters, of course, are analog and could also have digital counterparts.
With a sampling frequency of 10MHz .... alias frequencies occur beginning from 5MHz.That will help you decide how much you will have to attenuate the unwanted frequency components around Fs before they alias back into the signal bandwidth.
Hi,
With a sampling frequency of 10MHz .... alias frequencies occur beginning from 5MHz.
Example:
6MHz input will become 4MHz alias..
Thus a 5MHz filter will attenuate alias frequencies just by 3dB worst case.
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