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FETs have lower bias currents, is that correct?
Maybe.
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How do you observe the effects of bias current in a simulator?
Same way as in real life: set up a simple but non-trivial circuit and see how bad it screws-up.
What is "non-trivial"? Well, we can always reduce the effect of input bias current to Zero by shorting the inputs to ground. Problem solved. Except we also like our amplifiers to amplify, which means that we gotta put a signal in somewhere.
The most basic reason we care about bias current is when we C-R couple. We want to block DC and maybe bass from a source, yet still have a path for Base/Gate current to reach ground and set a DC level on the input pin. And with simulator accuracy, we can wire the amplifer for unity gain (remembering that whatever we get at unity gain may be worse at higher gains).
Three op-amps with 1 Meg input resistors. The AC source and capacitors are not needed to check DC bias currents, just to remind us why we don't just short-out the inputs and their annoying currents.
Top amp is "ideal", and shows zero volts across the 1Meg, zero bias current.
Middle amp is the popular LM324 with BJT inputs, showing 44 milliVolts.
Bottom amp is a BiFET similar to TL071, showing 30
microVolts.
(If I'd had a 5532 or 990 to throw in there, they would show most of a Volt of offset in a 1Meg resistor.)
"Clearly" the FET input beats the BJT input.
But that was 27 deg C. Try 85 deg C:
BJT bias tends to decline a bit when hot, FET leakage increases exponentially. It just happens these parts come to similar values at 85 deg C. It is true that in very wide-temp applications, you can sometimes do better with a tight BJT design, or at least it won't go wild above a certain temperature.
Yes, I agree there seems to be some funny-stuff here. The output voltages "should" be the same as the input voltages, since the feedback wire has no bias-current error. I suppose the op-amp models have some offset voltage in them. Op-amp models should be treated with EXTREME distrust: full modeling would clog your CPU, most models attempt only the gross behavior, and possibly not all the embarassing details. While I don't believe the exact values shown, certainly not the exactness shown (point oh two microvolts?), I do think the trend is valid. An LM324 will show measurable (on a simple VTVM) offset with a 1 Meg input resistor, a TL071 won't, not in the shop (maybe down in the oil-well). As Brad says: "input current won't necessarily be constant with input common-mode voltage, but most simulators probably ignore these effects."
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Set up a circuit as an integrator
Show-off. Sure, that's how you measure super-low DC current. But we simple audio people figure: if we don't see much DC across the grid resistor, that's all we need to know.