AF filter using opamps - substitution of opamps

[abraxalito]

Originally Posted by neazoi

If it is ok, could ththese be used with single supply as well in the circuit? (I see a balanced supply in the datasheet)

I agree with Mooly on the overkill of those ADI parts.

Single supply can be made to work yes - you can use something like a 5532 as a virtual ground generator. Otherwise called a 'rail splitter'. Or you can buy a (fairly expensive for what it is) dedicated device from TI : TLE2426.

Virtual Ground Circuits

[Mooly]

The diagram in the pdf is single rail, not split and uses a resistive divider to generate VCC/2 bias voltage.

[Mooly]

neazoi... all opamps of the types mentioned will all work on single rail.

Don't get confused on that... there is no problem with the PSU as shown.

[neazoi]

Thank you so much all of you.
I think I am going to be realistic and go for the cheap and tested on this circuit tl071
I would use some 0.1% tolerance resistors and good tolerance capacitors for the phasing networks to get good performance over temperature. These are cheap these days

[abraxalito]

0.1% tolerance resistors in this are just as big overkill as ADI opamps. If you really want to gild the lily, why not implement the whole thing digitally? After all, all pass networks as delay elements are always going to be a bit of a compromise...

[cliffforrest]

The OP circuit is for CW (ie Morse Code!) demodulation!

Not much point going on about opamp rolling, noise etc etc.

[DF96]

Exactly! The input signal probably has 20dB S/N and 5% distortion, so lets not get in a sweat about op-amps, component tolerance etc. Given the relatively high impedance a JFET input amp would seem best, and a cheap one will be just as good as an expensive one in this application.

Personally, I'm not too sure about the design. It has a narrow central peak, but broad skirts. I guess the question is how close to linear phase does it get across the passband?

[abraxalito]

Originally Posted by cliffforrest

The OP circuit is for CW (ie Morse Code!) demodulation!

Whaddya mean you've never dreamed of greater soundstage depth and added detail for your dahs and dits? Isn't Morse all about PRaT ?

[Nico Ras]

I agree fully with Mooly, the filter is for CW (continuous tone) communications, noise power density is directly related to bandwidth which is very limited. It does exactly what it says, it will retrieve coherent signal from what seems to be under the noise floor which is non coherent signal or what we refer to as noise. any op-amp will do the job equally well at this frequency.

[Nico Ras]

I would use two eight order elliptical filters, one as high and the other as low pass which would give far greater selectivity and use probably four components. Go look at the MAX7400 series.