Does the input bias current of opamps cause shot noise?

[safwatonline]

does the input bias current of opamps cause shot noise? or is this the case in case of BJT input pair only?

 

[FvM]

Re: current noise

Any current flow through a semiconductor junction, either forward or reversed biased, causes shot noise. In case of current compensated amplifiers (e. g. OP07, OP27), the shot noise generating current may be considerably higher than the OP input current.

 

[safwatonline]

current noise

Ok, let me rephrase the question does the input bias current cause shot noise in FETs/CMOSs as they do in BJTs.
the thing is i want to calculate the noise of an opamp with FET input and i was wondering whether i should consider bias current as shot noise source.
Like in CMOS, i think the input bias current shouldn't cause noise as it is leakage current through the gate with no junction at all, but i am not sure about FET (i am guessing it is the same as CMOS)

 

[FvM]

Re: current noise

My first point is that semiconductor junctions are only one possible case of current sources that involve charge carriers transitioning a barier, so that independent events are generating a possion statistics. Photoelectrons are another case and I guess, also charge carriers tunneling an isolator. The latter is probably a model for MOS gate current.

But you should ask a semiconductor specialists, I'm only a hobbyist in this regard. If the discussion is about CMOS IC, most of the input current is from surrounding junctions rather than from gate oxyd. So no matter if gate oyxyd current has shot noise, the junction current surely has. JFET gate current anyway.

Finally, if you look at a CMOS OP datasheet, you'll notice that the low frequency noise current density (that may be thought as caused by shot noise) is constant up to a few kHz only, increasing considerably with frequency. Obvioulsy other noise sources are dominant here.

 

[flatulent]

Re: current noise

All two port networks can be characterized by an equivalent input noise voltage generator and input current noise generator. Look at a datasheet for a jfet and you will see curves of these v.s. frequency.

 

[safwatonline]

Re: current noise

All two port networks can be characterized by an equivalent input noise voltage generator and input current noise generator. Look at a datasheet for a jfet and you will see curves of these v.s. frequency.

actually i am talking about whether the input bias current is a source of noise other than the current noise.
Do u mean that when the Data sheet states noise current and voltage then this is the total noise sources and i shouldn't look for any shot noise due to bias current?

 

[FvM]

Re: current noise

Why do you think that shot noise from bias current may be not included in noise current specification? It surely is, if a specification is present at all. For many devices, shot noise is a the dominant or at least an important contributor to specified noise current.

 

[safwatonline]

current noise

well, after reviewing some of articles on analog devices site i got that feeling (maybe i am not correct)
i will try to post what made me doubt that.