Noise of an Instrumentation Amplifier Circuit

[MattDuffADI]

Another example of how to calculate noise is on page 18 of the AD8429 datasheet: "Calculating the Noise of the Input Stage". Note that the AD8429 example also includes the Rg noise. To keep it simple, in our AD8226 video, we neglected the Rg noise, since it is typically fairly small compared to the other noise sources. However to have the most accurate estimate, add in the Rg noise as we did in the AD8429 example.

[MattDuffADI]

Unlike op amps, in amps have this funny property that some of the noise is dependent on gain and some of isn't. We denote these two terms in the datasheet as "eni" and "eno". These terms can be referred to input or output.

For example with AD8226 at G=10:

Referred to input: eni=22 nV/rt(Hz), eno =12 nV/rt(Hz)

Referred to output: eni=220nV/rt(Hz), eno=120 nV/rt(Hz)

[kishorekumar1988]

why do u have both input referred noise density as well as output referred noise density for the amplifier?

[izan009]

nice... very nice...

[MsHojat]

Damn those are pretty small numbers, lol. My instrumentation course never covered much about noise calculations, only general theory regarding noise such as how to deal with it.