Comparator applications

Key takeaways

Comparator applications belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Comparator applications to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Comparator applications from memory before moving on to harder problems.

Reference excerpt

A comparator is an electronic component that compares two input voltages. Comparators are closely related to operational amplifiers, but a comparator is designed to operate with positive feedback and with its output saturated at one power rail or the other. If necessary, an op-amp can be pressed into service as a poorly performing comparator, but its slew rate will be impaired.

Comparator

Bistable output that indicates which of the two inputs has a higher voltage. That is,

V out = { V S + if V 1 > V 2 , V S − if V 1 < V 2 , 0 if V 1 = V 2 , {\displaystyle V_{\text{out}}={\begin{cases}V_{{\text{S}}+}&{\text{if }}V_{1}>V_{2},\\V_{{\text{S}}-}&{\text{if }}V_{1}<V_{2},\\0&{\text{if }}V_{1}=V_{2},\end{cases}}}

where V S + {\displaystyle V_{{\text{S}}+}} and V S − {\displaystyle V_{{\text{S}}-}} are nominally the positive and negative supply voltages (which are not shown in the diagram).

Threshold detector

The threshold detector with hysteresis consists of an operational amplifier and a series of resistors that provide hysteresis. Like other detectors, this device functions as a voltage switch, but with an important difference. The state of the detector output is not directly affected by input voltage, but instead by the voltage drop across its input terminals (here, referred to as Va). From Kirchhoff's Current Law, this value depends on Vin and the output voltage of the threshold detector itself, both multiplied by a resistor ratio.

V + = R 2 R 1 + R 2 V i n + R 1 R 1 + R 2 V o u t {\displaystyle V_{+}={R_{2} \over {R_{1}+R_{2}}}V_{in}+{R_{1} \over {R_{1}+R_{2}}}V_{out}}

Unlike the zero crossing detector, the detector with hysteresis does not switch when Vin is zero; rather the output becomes Vsat+ when Va becomes positive and Vsat- when Va becomes negative. Further examination of the Va equation reveals that Vin can exceed zero (positive or negative) by a certain magnitude before the output of the detector is caused to switch. By adjusting the value of R1, the magnitude of Vin that will cause the detector to switch can be increased or decreased. Hysteresis is useful in various applications. It has better noise immunity than the level detector, which is used in interface circuits. Its positive feedback has a faster transition, so it is used in timing applications such as frequency counters. It is also used in astable multivibrators found in instruments such as function generators.

Zero crossing detector A zero crossing detector is a comparator with the reference level set at zero. It is used for detecting the zero crossings of AC signals. It can be made from an operational amplifier with an input voltage at its positive input (see circuit diagram). When the input voltage is positive, the output voltage is a positive value; when the input voltage is negative, the output voltage is a negative value. The magnitude of the output voltage is a property of the operational amplifier and its power supply. Applications include converting an analog signal into a form suitable for frequency measurements, in phase locked loops, or controlling power electronics circuits that must switch with a defined relationship to an alternating current waveform. An example detector could exploit the property that the instantaneous frequency of an FM wave is approximately given by

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Comparator applications

Start with the simplest possible case. Write down what Comparator applications claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Comparator applications before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Comparator applications ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Comparator applications

In research: Comparator applications appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Comparator applications in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Comparator applications is common in secondary-school and first-year university syllabi. It links to neighbouring topics Analog circuits, Electronic amplifiers, so understanding it makes those chapters shorter.
In everyday life: Look for Comparator applications outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Comparator applications in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Comparator applications means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Comparator applications out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Comparator applications in simple terms?

A comparator is an electronic component that compares two input voltages. Comparators are closely related to operational amplifiers, but a comparator is designed to operate with positive feedback and with its output saturated at one power rail or the other.

Why does Comparator applications matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Comparator applications?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Comparator applications.