eem2am
Banned
op amp offset
Hello….
It is known that op-amps give slightly inaccurate output voltages due to …..
1) Input bias currents
2) Input offset
So, I realise that an op-amp has an input offset that means that when used with negative feedback, its output voltage will not be zero when it has zero volts between its inverting (V-) and non-inverting (V+) inputs.
I am aware that this offset is gotten-rid-of by using a pot at dedicated “offset-null” pins…..OR by putting some high value resistor between the positive supply of the op-amp and the inverting input.
Also…
… I am aware that an op-amps V+ and V- inputs draw input bias currents….and that these bias currents create voltages at the inputs, since they flow through whatever resistors are biasing the op-amp……
..in order to mitigate this problem with an inverting op-amp, a resistor of value R(feedback//R(in) is put from V+ to ground.
…..However, in reality, the op-amps “input offset” is actually caused by the fact that the op-amps “input bias currents” are actually NOT equal…(?).
…so in actual fact, “input offset” is just another problem caused by “input bias currents”. (?)
As such, if I want to mitigate (get rid of) these bad effects, then surely I only need to use ONE of the above correcting steps?……
…in other words……rather than use a resistor from V+ to ground AND the offset-null pot……….-I can simply just use the offset-null pot to deal with both the “input bias current” problem and the “input offset” problem.
Do you believe this is correct?
Thankyou for reading.
Hello….
It is known that op-amps give slightly inaccurate output voltages due to …..
1) Input bias currents
2) Input offset
So, I realise that an op-amp has an input offset that means that when used with negative feedback, its output voltage will not be zero when it has zero volts between its inverting (V-) and non-inverting (V+) inputs.
I am aware that this offset is gotten-rid-of by using a pot at dedicated “offset-null” pins…..OR by putting some high value resistor between the positive supply of the op-amp and the inverting input.
Also…
… I am aware that an op-amps V+ and V- inputs draw input bias currents….and that these bias currents create voltages at the inputs, since they flow through whatever resistors are biasing the op-amp……
..in order to mitigate this problem with an inverting op-amp, a resistor of value R(feedback//R(in) is put from V+ to ground.
…..However, in reality, the op-amps “input offset” is actually caused by the fact that the op-amps “input bias currents” are actually NOT equal…(?).
…so in actual fact, “input offset” is just another problem caused by “input bias currents”. (?)
As such, if I want to mitigate (get rid of) these bad effects, then surely I only need to use ONE of the above correcting steps?……
…in other words……rather than use a resistor from V+ to ground AND the offset-null pot……….-I can simply just use the offset-null pot to deal with both the “input bias current” problem and the “input offset” problem.
Do you believe this is correct?
Thankyou for reading.