I am trying to understand how varying the input differential pair quiscient current in an op amp will affect its: a) input bias current, b) input current noise, c) input voltage noise. Based on experience, I guess that (a) and (b) increase with tail current, whereas (c) decreases. But my question is the scaling of the dependences.
- I suppose the voltage noise depends inversely on the square root of tail current, because that is essentially what you get from paralleling op amps. Is this correct irrespective of the input transistor type (Bipolar, JFET, MOSFET)?
- Conversely, do bias current and current noise increase by the square root of tail current or do they increase faster ? The same argument from paralleling op amps suggests that the input bias current rises linearly with tail current, but I am not sure it is valid for FETs. This article indeed says that there is no relation in FETs between their bias current and the current flowing through the transistor.
- This article states that bias current and current noise are linearly proportial for JFET opamps. Does the same hold for other transistor types? Why does the input bias current for FETs depend on the channel current (qualitative explanation) ?
Kind regards
