Variations in Feedback Circuits 

Since the behavior of the amplifier circuit is controlled almost entirely by the input and feedback circuits, we can control the circuit behavior in many ways by using different components and controlling their arrangement. Here are some practical examples.
A very common function performed by analog computers is the electronic equivalent of mathematical integration. This enables the analog computer to directly solve differential equations.
The opposite of integration is differentiation. This can be done in analog computers, but to a much more limited extent than integration.
Since the gain of the op amp is controlled by the input and feedback circuits, what happens if we use a nonlinear feedback element?
Op amps don't have to be wired to invert the signal. You just have to use a slightly different calculation to find the gain.
What happens if we combine inverting and noninverting methods?
An improved difference amplifier suitable for use in many kinds of delicate and sensitive electronic instruments.
Sometimes we need more output current than the basic op amp can provide. Can we arrange that without upsetting the gain calculations?
Sometimes we need to process a signal using only one polarity. You wouldn't want to use this sort of rectifier circuit in a power supply, but for signal processing it works very nicely.
We can add some circuitry to get a fullwave precision rectifier that works as well as the halfwave version.


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