Re: Low noise IF3601/02 don't meet specs


"Fred Bartoli"
<fred._canxxxel_this_bartoli@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> schrieb im
Newsbeitrag news:43b5c21c$0$21690$626a54ce@xxxxxxxxxxxxxxx
>
> "Helmut Sennewald" <helmutsennewald@xxxxxxxxxxx> a écrit dans le message
de
> news:dp49qm$4ne$02$1@xxxxxxxxxxxxxxxxxxxx
> > "Fred Bartoli"
> > <fred._canxxxel_this_bartoli@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> schrieb
im
> > Newsbeitrag news:43b59f8e$0$21714$626a54ce@xxxxxxxxxxxxxxx
> > >
> > > "Winfield Hill" <Winfield_member@xxxxxxxxxxx> a écrit dans le message
de
> > > news:dp3v290roh@xxxxxxxxxxxxxxxxxx
> > > > Fred Bartoli wrote...
> > > > > Joe G (Home) wrote,
> > > > >> Fred Bartoli wrote,
> > > > >>>
> > > > >>> they are spec'd at 300pV/rtHz @ 5mA and 100Hz and should get
> > > > >>> down near 260pV @ 100kHz.
> > > > >>>
> > > > >>> Well for the IF3601 and both side of the IF3602 dual, I get
> > > > >>> 400pV/rtHz @ 5mA, and the noise PSD is almost flat.
> > > > >>
> > > > >> In the old days - silicon manufacturers used to publish the
> > > > >> test setups to acheive the data *** spec's. ...
> > > > >>
> > > > >> You can't say the FET doesn't meet spec's until you reproduce
> > > > >> the mfg'ers test setup...
> > > > >
> > > > > Of course I can. I duplicate the working conditions of the
> > > > > data*** (5mA/3V) in a test setup that's designed to add not
> > > > > more than 2% to the measured noise. Not a big deal really.
> > > >
> > > > Spell it out for us please. At the 100pV noise level it's easy
> > > > to mistakenly let the gain-setting components add to the measured
> > > > noise. You're claiming under 50pV of test-setup generated noise?
> > > > That requires 0.16-ohm resistors, or more likely none at all, like
> > > > my HP transistor noise meter, which runs the JFET flat out with a
> > > > grounded source, and separately measures its gain, to determine
> > > > the divisor required to obtain the narrowband input noise. Tell
> > > > us more about your measurement technique.
> > > >
> >
> >
> > Hello Fred,
> >
> > Have you done a reference measurement before you
> > inserted the JFET? How much noise have you measured
> > in this pre-measurement?
> > I just want be sure that you haven't overlooked something.
> >
>
> Of course. When doing such delicate measurements you want to carefully
> double check all the parameters. I made measurements with differents
methods
> which all agree pretty well if you're carefull enough. I've now spent
quite
> some time chasing all errors and I'm pretty confident in the results...
> unfortunatly.
> Anyway I'll probably make another last try next week, because I'm not
> satisfied with the remaining discrepancy between the predicted noise from
gm
> and the measured one.
>
>
> > Is your 1k resistor ok regarding extra noise?
> > I have read that thickfilm resistors have more noise than
> > you would expect from the basic noise formula.
> > This extra noise may depend from the voltage across
> > the resistor and the current flowing through it.
> > Who knows more about this?
> >
>
> Excess noise in resistors comes from resistors fluctuations and has a
> 1/sqrt(f) dependency. It can only be noticed at low frequency and vanishes
> under Johnson noise above some (low) frequency.
> The measurements I have made are at much higher frequencies to keep excess
> noise well below thermal noise. As a result the noise PSD is fully flat,
as
> expected.
>
> Excess noise might be a problem in the final preamplifier design (BW
extends
> down to 0.1Hz) but that's another story.
>
>
> --
> Thanks,
> Fred.

Hello Fred,

I looked a little bit with Google for "thick film noise smt".

http://www.niccomp.com/Products/smt/NRCnoiselevel0801.pdf

Even for a 1206 resistor they show about 1uV noise for 5V across
a 1k-resistor. The question is now about the used noise measurement method.

>From this paper one could think it's a measurement at a center
frequency of 1kHz with 1 decade bandwidth. I am not sure it's
really the same measurement method as used in the data*** above.
http://www.mini-systemsinc.com/msithick/msipaper.pdf

I would be happy if somebody could reveal this standard
noise measurement method used for this extra noise of thickfilm
SMT resistors. The result is given in uV/V or in dB.


Best regards,
Helmut



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