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What kind of noise is in an op amp?
There are a number of noise sources within an op amp (resistor noise, current noise, KT/C noise, etc.), but it is customary to model them externally as a voltage noise which appears differentially across the two inputs and two current noise sources, one in each input.
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:
What is the input bias current of an opamp?
Most (nonideal) opamps have a finite input resistance, and this means that a tiny current flows into or out of the input terminals. This current is called “input bias current”, and it varies with the voltage at the inputs.
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.
Which is better bipolar op amp or FET op amp?
Bipolar op-amps have traditionally had less voltage noise than FET ones, but have paid for this advantage with substantially greater current noise –today, FET op-amps, while retaining their low current noise, can approach bipolar voltage-noise performance. Q. Hold it! 1 nV/√Hz?
Why do bias compensated op amps have higher noise?
Bias-compensated op-amps have much higher current noise than one can predict from their input currents. The reason is that their net bias current is the difference between the base current of the input transistor and the compensating current source, while the noise current is derived from the RSS sum of the noise currents.
What is the noise figure of an amplifier?
The noise figure (NF) of an amplifier (expressed in dB) is a measure of the ratio of the amplifier noise to the thermal noise of the source resistance.