S5-4.2 Op-Amp Applications
You can design summing and difference amplifiers, ideal and practical integrators and differentiators, sample and hold circuits, comparators, Schmitt triggers and a triangular waveform generator.
This unit is the op-amp earning its keep: the same device becomes an adder, a subtractor, an integrator or an oscillator depending only on the feedback network around it. The practical integrator differs from the ideal one by a resistor across the capacitor, and knowing why - the ideal version saturates on any DC offset - is the difference between a circuit that works and one that latches up. The Schmitt trigger's hysteresis is the standard cure for a comparator chattering on a noisy input, and it recurs everywhere in digital interfacing.
Work through these
Summing amplifier
The device earning its keep: the same part becomes an adder because of the network around it. It is the cleanest demonstration that the feedback network, not the amplifier, defines the function.
Difference amplifier
Subtraction, and the first step towards rejecting noise common to both inputs. It leads directly to instrumentation amplifiers if you go further in this direction.
Ideal and practical integrator
The ideal version saturates on any offset at all, and the practical one adds a resistor to stop it. Knowing why that resistor is there is the difference between a circuit that works and one that latches up.
Ideal and practical differentiator
The mirror operation, with a mirrored problem: it amplifies high frequency noise enthusiastically. The practical version tames it the same way, by limiting the gain where you do not want it.
Sample and hold circuit
Freezing a value long enough for something else to read it. It is the front end of every converter in the next topic, so it is not an aside.
NPTEL: Analog Electronic Circuit · CourseThe comparator
Running the device without feedback, so it swings to one rail or the other. Simple, and it misbehaves badly on a noisy input, which the next item fixes.
Schmitt trigger with and without reference voltage
Hysteresis as the standard cure for a comparator chattering on a noisy edge. This one recurs everywhere in digital interfacing, so it is worth being able to design rather than recognise.
Triangular waveform generator
Two of the circuits above wired into a loop until they oscillate. It is a satisfying end to the topic because it uses the integrator and the trigger together.
Lab: implement arithmetic circuits using an op-amp
The bench version of the arithmetic circuits. Getting the same answers you predicted on paper is the check that the ideal rules are being applied correctly.
NPTEL: Digital Circuits · CourseLab: implement waveform generation using an op-amp
The bench version of the oscillator. Watching the triangle and the square appear together makes the loop structure obvious in a way the schematic does not.
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