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Sci.Electronics.Basics -> Calculating Input Noise Voltage
There are 4 messages in this thread.
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Author: MRWDate: 13:07 31-05-07
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I was just checking out various opamp datasheets. I encountered this
opamp:
http://focus.ti.com/lit/ds/symlink/tlv2784.pdf
In the few lines of text, it says that the input noise voltage is 9 nV/
sqrt(Hz) at 10kHz. But in the table at the bottom of the page, it says
that the input noise voltage is 18 nV/sqrt(Hz) at 1kHz.
How did they calculate this?
I'm curious because if I were to use an opamp (not necessarily this
one) then I would like to know how much input noise voltage it
contributes for a certain bandwidth, for instance audio band from 20Hz
to 20kHz. There was another discussion that I saw (don't remember the
link) that mentioned that at one particular design, the amplifier was
designed with a 40dB gain and the input noise got amplified to about
100mV.
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Author: Phil AllisonDate: 19:46 31-05-07
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"MRW" <mr.whatever@gmail.com>
** Groper fool alert.
>I was just checking out various opamp datasheets. I encountered this
> opamp:
> http://focus.ti.com/lit/ds/symlink/tlv2784.pdf
>
> In the few lines of text, it says that the input noise voltage is 9 nV/
> sqrt(Hz) at 10kHz. But in the table at the bottom of the page, it says
> that the input noise voltage is 18 nV/sqrt(Hz) at 1kHz.
>
> How did they calculate this?
** See figure 19 ??
See how the EIN goes up dramatically at frequencies below 3 kHz ?
Go check some other op-amps - discover they are not all like that.
> I'm curious because if I were to use an opamp (not necessarily this
> one) then I would like to know how much input noise voltage it
> contributes for a certain bandwidth, for instance audio band from 20Hz
> to 20kHz.
** Normally just multiply the typical or 1 kHz EIN figure by 141 (= sq
rt 20,000)
....... Phil
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Author: MRWDate: 22:45 31-05-07
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On May 31, 7:46 pm, "Phil Allison" <philalli...@tpg.com.au> wrote:
> "MRW" <mr.whate...@gmail.com>
>
> ** Groper fool alert.
>
> >I was just checking out various opamp datasheets. I encountered this
> > opamp:
> >http://focus.ti.com/lit/ds/symlink/tlv2784.pdf
>
> > In the few lines of text, it says that the input noise voltage is 9 nV/
> > sqrt(Hz) at 10kHz. But in the table at the bottom of the page, it says
> > that the input noise voltage is 18 nV/sqrt(Hz) at 1kHz.
>
> > How did they calculate this?
>
> ** See figure 19 ??
>
> See how the EIN goes up dramatically at frequencies below 3 kHz ?
>
> Go check some other op-amps - discover they are not all like that.
>
> > I'm curious because if I were to use an opamp (not necessarily this
> > one) then I would like to know how much input noise voltage it
> > contributes for a certain bandwidth, for instance audio band from 20Hz
> > to 20kHz.
>
> ** Normally just multiply the typical or 1 kHz EIN figure by 141 (= sq
> rt 20,000)
>
> ....... Phil
Thanks, Phil! I'll take a look at other datasheets. Got any opamps you
can recommend for audio?
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Author: Phil AllisonDate: 23:29 31-05-07
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