Does input resistance in negative feedback increase input offset current of op amp?


by gothloli
Tags: current, feedback, increase, input, negative, offset, resistance
gothloli
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#1
Dec11-11, 10:35 AM
P: 30
If it is in inverting or non-inverting configuration, will the input resistance increase the mismatching of the bias currents, or will it only increase the error voltage?
Please Explain like your talking to an idiot, I need to write an essay on this, and I don't know what to do!

Also how would you connect one of the inputs to ground, say for example if it's an inverting amp, how would you connect the non-inverting input to ground on a solderless breadboard?
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sophiecentaur
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#2
Dec11-11, 11:33 AM
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Hi.
It's usually recommended that you connect the non-inverting input to ground via a resistance of equal value to that seen by the other input. This reduces the imbalance in input currents to the bases of the input stage, i believe.
shayaan_musta
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#3
Dec13-11, 02:45 PM
P: 168
Your answer is "Does input resistance in negative feedback increase input offset current of op amp?"

Answer is yes.

Therefore we use and OM(offset minimizing) resistance at the non inverting(connected at ground). Normally OM is equal to the value of input resistance at inverting input(connected with supply). OM helps to minimizes input offset current which is caused by negative feedback.

yungman
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#4
Dec13-11, 03:02 PM
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Does input resistance in negative feedback increase input offset current of op amp?


The input resistance of the op-amp has nothing to do with the input bias or offset current.....Period. Nothing at the input can affect the input bias or offset current nor the input offset voltage......Period.

The arrangement of the negative feedback WILL affect the total OUTPUT offset voltage. This might be what you meant by error voltage.

1) Output offset voltage cause by input bias current:

Input bias current has to got through the resistors that connect to the input. This will cause a voltage developed across the resistors. Then this voltage will be amplified by the closed loop gain of the op-amp and become the output offset error.

2) Output offset voltage cause by input offset voltage:

This will be amplified by the gain of the closed loop gain of the op-amp.

The total output offset voltage is the sum of the two above. This is a very simplistic view. You have to work out the detail calculation. But again, to be clear. Input offset current, input bias current and input offset voltage are ONLY op-amp dependent, they do not change no matter what configuration of the closed loop feedback.
yungman
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#5
Dec13-11, 06:33 PM
P: 3,844
How come this is moved here? This is every bit electronics. It's about op-amp input bias current!!!


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