Input Resistance & Bias Currents: Explained Simply

In summary: The arrangement of the negative feedback WILL affect the total OUTPUT offset voltage. This might be what you meant by error voltage.
  • #1
gothloli
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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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  • #2


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.
 
  • #3


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.
 
  • #4


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.
 
  • #5


How come this is moved here? This is every bit electronics. It's about op-amp input bias current!
 

FAQ: Input Resistance & Bias Currents: Explained Simply

1. What is input resistance?

Input resistance is the measure of how much resistance a circuit or device presents to an incoming electrical signal. It is typically measured in ohms and is important in determining the strength and quality of an electrical signal.

2. How is input resistance different from output resistance?

Input resistance is the resistance seen by an incoming signal, while output resistance is the resistance seen by an outgoing signal. Input resistance is typically higher than output resistance, as it reflects the resistance of the entire circuit or device, while output resistance only reflects the resistance of the output stage.

3. What is bias current?

Bias current is the small amount of current that flows through a circuit or device even when no input signal is present. It is typically caused by imperfections in the circuit components and can affect the accuracy and stability of the circuit's output.

4. How does input resistance affect circuit performance?

Input resistance affects circuit performance by influencing the strength and quality of an incoming signal. A higher input resistance can improve the signal-to-noise ratio and overall sensitivity of the circuit, while a lower input resistance may result in a weaker and noisier signal.

5. How can input resistance and bias currents be minimized?

Input resistance and bias currents can be minimized by using high-quality components, properly designing and constructing the circuit, and implementing techniques like shielding and filtering. Additionally, using operational amplifiers can help reduce input resistance and bias currents in certain circuits.

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