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What is the purpose of the feedback resistor in an operational amplifier?
The feedback resistor connects the output of to op-amp to its inverting-input (Negative feedback). This is called closing the loop. The value of this feedback resistor determines the overall gain of the op-amp as well as the frequency range it can maintain this gain.
How can you improve the stability of an op amp?
To ensure stability, the value of RX should be such that the added zero (fZ) is at least a decade below the closed loop bandwidth of the op amp circuit. With the addition of RX,circuit performance will not suffer the increased output noise of the first method, but the output impedance as seen by the load will increase.
Why does amplifier gain reduce at high frequencies?
The low input impedance offered by the capacitor {C} present in the circuit and also the transistor gain reduces the output at high frequency are the reason off gain falling down at high frequencies.
Why is a feedback resistor used in an op-amp?
And another example, from the AD797 data sheet: One reason the feedback resistor may be used is to match the output impedance of Vin. Real Op-amps have input current bias and input current offset. Take for example this representative circuit:
How to calculate the value of a feedback resistor?
Calculate the Feedback Resistor. The value of the feedback resistor must be selected such that the voltage gain is equal to the number of inputs. In our case we will need a gain of 4.
Why do we use negative feedback in an opamp?
This current is called “input bias current”, and it varies with the voltage at the inputs. Since most opamp circuits use negative feedback to keep the two inputs at the same voltage, this means that for any given voltage, the current through both inputs will be the same.
How is distortion cancelled in an op amp?
It is possible to cancel this distortion by placing a resistance equal to the source impedance in the op amp’s feed-back loop. This produces an identical distortion signal at the op amp’s inverting input. Because the distortion is now common to both inputs, it is removed by the op amp’s common-mode rejection.