[volt-nuts] Why discrete JFET differential pair before opams?

[Brian Smith]

Interesting that the Keithley 148 has an input noise of 0.2nV RMS and had
its heyday in the 1970s. The147 is not as good but good enough to have a
30nV lowest range. I have reliably measured 5nV with my 147. Most of a day
is required to warm up the instrument and let the DUT, connections and
cables stabilize.

Setting the DUT on top of the instrument shows some coupling of the 147
transformer and the DUT/cables. Had to move the DUT away from the
instrument.

I used a Keithley 2450 to force 1A into a 5 nano ohms precision 4-wire
short manufactured by Ohm Labs.

Brian
VintageNut on eevblog



On Sat, Aug 29, 2015 at 3:54 PM, Attila Kinali <attila at kinali.ch> wrote:

> On Sat, 29 Aug 2015 20:17:55 +0200
> Andreas Jahn <Andreas_-_Jahn at t-online.de> wrote:
>
> > the LSK389 is usually used for very low noise applications.
> > (the title already states this: 40nVpp).
> >
> > What 1/f noise has the LTC6241?
>
> Ah! Now it makes sense! The LTC6241 has an input noise voltage
> of typ 550nV p-p (0.1Hz to 10Hz).
>
> Thanks!
>
>                         Attila Kinali
>
> --
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>
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