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The open-loop gain is a physical attribute of an operational amplifier that is often finite in comparison to the ideal gain. While open-loop gain is the gain when there is no feedback in a circuit, an operational amplifier will often be configured to use a feedback configuration such that its gain will be controlled by the feedback circuit components.
The magnitude of A OL is not well controlled by the manufacturing process, and so it is impractical to use an open-loop amplifier as a stand-alone differential amplifier. Without negative feedback, and optionally positive feedback for regeneration, an open-loop op amp acts as a comparator, although comparator ICs are better suited. [3]
where Z dif is the op-amp's input impedance to differential signals, and A OL is the open-loop voltage gain of the op-amp (which varies with frequency), and B is the feedback factor (the fraction of the output signal that returns to the input). [3] [4] In the case of the ideal op-amp, with A OL infinite and Z dif infinite, the input impedance ...
In addition, dominant-pole compensation allows control of overshoot and ringing in the amplifier step response, which can be a more demanding requirement than the simple need for stability. This compensation method is described below: Let be the uncompensated transfer function of op amp in open-loop configuration which is given by:
Also, in a DC steady state, an ideal capacitor acts as an open circuit. The DC gain of the ideal circuit is therefore infinite (or in practice, the open-loop gain of a non-ideal op-amp). Any DC (or very low frequency) component may then cause the op amp output to drift into saturation. [3]
Schmitt triggers are typically used in open loop configurations for noise immunity and closed loop configurations to implement function generators. Analog-to-digital conversion: The Schmitt trigger is effectively a one bit analog to digital converter. When the signal reaches a given level it switches from its low to high state.
When the input becomes (even slightly) negative, the opamp runs open-loop, as there is no feedback signal through the diode. For a typical opamp with high open-loop gain, the output saturates. If the input then becomes positive again, the op-amp has to get out of the saturated state before positive amplification can take place again.
Figure 5: Op-amp differential amplifier. An operational amplifier, or op-amp, is a differential amplifier with very high differential-mode gain, very high input impedance, and low output impedance. An op-amp differential amplifier can be built with predictable and stable gain by applying negative feedback (Figure 5).