What is Comparator: Definition and 47 Discussions

In electronics, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals



{\displaystyle V_{+}\,}


{\displaystyle V_{-}\,}
and one binary digital output



{\displaystyle V_{\rm {o}}\,}
. The output is ideally

















{\displaystyle V_{\rm {o}}={\begin{cases}1,&{\mbox{if }}V_{+}>V_{-}\\0,&{\mbox{if }}V_{+}<V_{-}\end{cases}}}
A comparator consists of a specialized high-gain differential amplifier. They are commonly used in devices that measure and digitize analog signals, such as successive-approximation ADCs, as well as relaxation oscillators.

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  1. Mr su

    Can this comparator accept negative voltage as its negative supply?

    I check the datasheet of LM 319 high speed comparator online. I was wondering if LM 319 can accept negative supply voltage(-10V) and its possible to produce a 10V to -10V square wave which oscillates along origin rather than just 10V to 0v as shown below.
  2. S

    DIY large aperture optical comparator

    Hi. In machine shops optical comparators have been used for a really long time to measure and inspect complex and usually small parts. But they are usually for small parts and they are usually really expensive machines. How can i do this for cheap for larger parts like for example for making...
  3. jisbon

    Engineering Building a 2 bit comparator using either....

    So I got this question while coming across, and I would like to seek some advice/tips for these types of questions. 1) Assuming I want to try and build using MUXs, I will get the truth table of both a 2 bit comparator and MUXs. In this case: For comparator: And for MUX: So from what I...
  4. D

    How to make a comparator out of an opamp

    I have an operational amplifier. I am Trying to make a comparator out of It. I built a voltage divider to provide Different voltages. But I either get The same voltage output regardless Of input or the voltage is too high I think. How do you make a comparator out of an operational amplifier?
  5. Tracey3

    Capacitor on ground connection of Comparator input

    So I am stumped by why these capacitors are there, to my understanding the capacitor C3 acts as a low pass filter but then I don't quite understand the purpose of C1 and C2 as indicated on the picture.
  6. akaliuseheal

    Reading datasheets to pick a comparator

    Hello, I've got a voltage comparator, well only on schematics, I need to chose one and I need some help interpreting datasheet. The datasheet I was looking at is of a lm393. My input voltage ranges from -7.8V to +7.8V. The datasheet says -0.3 to something. So it's not usable, right? I was also...
  7. akaliuseheal

    Hysteresis of a voltage comparator

    Hello, I am designing a circuit which basically takes two voltages (V1,V2) and based upon which one of the two is greater, turns corresponding LED. So, I have got to the part where I have output from differential op amp that is the input of the inverting voltage comparator with hysteresis...
  8. A

    Window Comparator: Understanding the Output Behavior and Common Errors

    So I've been reading an intro book to electronics and I got to a section about operational amplifiers. It talks about different uses of them and how they can be used as comparators. It then talks about a specific comparator called a window comparator which will output a positive voltage if the...
  9. peroAlex

    Designing a 2-bit Comparator with NOR gates

    At our class on digital structures, this assignment has been given. It's a preparation for upcoming lab work, and I'm not sure my design is correct. Is anyone please willing to check it out? 1. The problem statement, all variables, and given/known data Design a two-bit comparator using NOR gates...
  10. T

    Operational Amplifier Comparator Circuit

    Homework Statement The variation with time t of the potential Vin at the inverting input of the op-amp is shown in Fig. 10.2. On the axes of Fig. 10.2, draw the variation with time t of the output potential of the op-amp. (pictures attached) Homework Equations The potential divider equation to...
  11. D

    NTC and comparator to detect temperature trip point

    In "The Art of Electronics" the following is said: "A comparator in a circuit is a handy device that switches its output according to the relative voltages at its two input terminals. There is a temperature sensing device, a thermistor, which decreases in resistance by about 4%/°C. So we’ve made...
  12. P

    A question about an opamp or comparator application

    hello dears i have a question at op amp could i use the comparator to compare between to differential signals .. more specific if i have tow signals out of phase (180) and unequal amplitude could i use op amp comparator or differential amplifier to distinguish which of them is higher amplitude ??
  13. J

    Understanding Comparator and Window Comparator Functionality in Op-Amps

    Hi, While studying opamps I came across comparator and window comparator. I had trouble understanding case of Vin > 2/3 Vcc. As per waveform, comparator 1 is functional and o/p goes negative. But isn't now Vin also more than 1/3 Vcc, so shouldn't comparator 2 make o/p positive. Also when Vin...
  14. S

    C# Is it possible to override the comparator < in C#?

    Is it possible to override the < operator in C#? Note: I'm saying override, not overload. I ask because, if there is, then I think I have discovered an O(1) sorting algorithm.
  15. C

    Need a solution for comparator circuit

    I have problem with this circuit. Normally when vP>vN (if I set vN>0.4V), output vQ is equal 5v. But when I set vN < 0.4V, output is not true, it is always 5V not only for vP< vN but also vP>vN. I need to design ADC circuit, and that is comparator block. Need some suggestions. Help me . I...
  16. ichabodgrant

    Comparator design using a 4-bit adder

    Homework Statement Hi, it's me again. Now I am going to design a 4-bit magnitude comparator using just ONE 4-bit adder and infinitely large number of gates (AND, OR, NOT, NAND, NOR, XOR, XNOR) for signed numbers (negative binary). Homework Equations A > B => A3barB3 + A2barB2x3 +...
  17. ichabodgrant

    Op-amp as a comparator (analog-to-digital conversion)

    Homework Statement Okay, This time it's an exam question. I am doing some past papers and there are questions about comparators which are not introduced in this course (this course is preliminary course for engineering students who are interested in electrical, electronic or computer...
  18. D

    Understanding the Use of Comparator for Digital Integrator

    https://www.physicsforums.com/threads/up-down-counter-overflow-74191.223044/#post-1655758 I am trying to build a digital integrator as specified on this thread. I do not understand the use of comparator in the circuit. Can anyone explain?? maybe the original poster. I am new to this .
  19. K

    What is the correct answer for the 4 bit magnitude comparator homework?

    Homework Statement Homework EquationsThe Attempt at a Solution As long as A = 1, its true, So options (A) and (C) are wrong. My ans is (E). Right?[/B]
  20. C

    Comparing 2-Bit Numbers with a Single Decoder and Standard Logic Gates

    < Mentor Note -- thread moved to HH from the technical engineering forums, so no HH Template is shown > Is there a way to create two bit numbers comparator using one 2 to 4 decoder and standard logic gates?
  21. J

    Is My Comparator Circuit Textbook Explanation Incorrect?

    Homework Statement We have to answer questions from a particular circuit (comparator) in our textbook for homework. The circuit is attached to this thread. I haven't started the questions yet as I don't even understand the circuit! Based on my notes I think my textbook is wrong and would...
  22. W

    Efficient CMOS Comparator Circuit for PWM Experiments with Sawtooth Generator

    I have been experimenting with PWM circuits and I came across this CMOS comparator that seems to work well with the sawtooth generator I am using. I feed a sawtooth wave to the gate of the PMOS M3 transistor and the reference voltage I am comparing to Vin the PMOS M4. I noticed that the...
  23. M

    Engineering Counter and comparator circuits connected

    Hi all, I need serious help here. I have to build two types of circuits as shown in the attached. The second one shows the circuit when the comparator's output is returned to the CLP. The IC's used here are IC 85 and IC 393 and the prototyping board used here is NI ELVIS 2. I think I have...
  24. C

    Connect High/Low Level Alarm Circuit with 6 LM741 Op Amps

    Hello, I completed this circuit with 6 op amps LM741. Now I want to connect any high and low level alarm circuit. I have found and tried some solutions but I didn't get it to work. Can you give me some advice how to do it?
  25. JJBladester

    Confusion about open-loop op-amp comparator operation

    Homework Statement Determine the output level (maximum positive or maximum negative) for each comparator in Figure 4-52. Homework Equations A_{ol}=\frac{V_{out}}{V_{in}} The Attempt at a Solution I am new to comparators but I thought that since all of these op-amps are...
  26. T

    Voltage comparator in a photo sensing circuit

    Hello, I attached a picture below but I am confused as to how the voltage comparator is comparing the two inputs (I know how a comparator works). The test points are running down to the two inputs but wouldn't the voltage always be identical across them since voltage doesn't drop in a parallel...
  27. mishima

    Building comparator from discrete components?

    Hi, I'm interested in building a breadboard version of the simplest comparator using transistors and resistors. Ultimately I'd like to understand the LM393 but looking at the datasheet schematic, it seems quite complicated. I was hoping there was a simpler comparator I could mimic to start out...
  28. Femme_physics

    Op-amps how could this possibly be a comparator?

    I'm asked which type of op-amps these are I think it's clear the SECOND one is a comparator, but the FIRST one is an inverter IMO. It has a feedback loop. If it has a feedback loop, it can't possibly be a comparator! Am I right or what? The solution manual my teacher made, had them both...
  29. D

    How can an Op Amp voltage comparator be used as a voltage controlled switch?

    Hi I am trying to create a circuit which i can use as a voltage controlled switch. I have 2 voltage inputs, ** A constant 3V source V1, ** A source which charges up to 3.5V and then slowly discharges V2. I would like to amalgamate both sources so as when V2 discharges...
  30. A

    Build 1 bit comparator using 2 to 4 decoder?

    build 1 bit comparator using "2 to 4" decoder?? Homework Statement The Attempt at a Solution worked out truth table: A B A>B A<B A=B 0 0 0 0 1 0 1 0 1 0 1 0 1 0 0 1 1 0 0 1 prty sure that's right. just need part B...
  31. M

    Engineering Set time delay for a comparator Op-amp circuit

    Homework Statement [See attached diagram] I'm trying to design a circuit that connects to the input terminals of the noninverting input of this comparator circuit such that: -The input to my circuit consists of a SPST switch and a 9 volt battery -When the switch is thrown on, there would be a...
  32. L

    Comparator hysteresis resistors & toggle rate

    I have a comparator ckt with external hysteresis. When I apply a square wave input everything works fine. The trip points are as designed, output goes high/low etc. But when I increase the duty cycle of the square wave to say beyond 75%, the output just stays high. I was playing with the...
  33. L

    Designing Comparator Circuits with 2 Different Thresholds

    I am trying to design a comparator which is required to have 2 different switching thresholds. The comparator +ve input is connected to a signal source (triangle wave). The -ve is connected to a reference voltage. The first threshold will be say Vth+ = 3V and Vth- = 1V and second...
  34. L

    Comp. Prop Delay: Significance & How to Choose High Speed Comp

    How is comparator prop delay significant? It's just delay, isn't it. Input occurs at say, t secs, output will occur at t+x secs. I am looking for a high speed comparator, I don't understand why manufacturer's classify speed based on propagation delay. Isn't rise time the factor that decides...
  35. L

    Designing Comparator with Discrete BJTs

    Just wondering how would one design a comparator using just discrete BJTs.
  36. D

    LED comparator for RF circuits

    I have a question about making an LED light up when sensing audio. Right now, I'm using Super-Regenerative receivers and testing various components of them. Using a signal generator, my audio speaker squeals, as it should, when on the right frequency. When it's not on the right frequency, I hear...
  37. F

    Why Is My LM339N Quad Comparator Not Changing Output?

    Hello, Im having problems with my circuit, I am using a quad comparator IC (LM339N) but for some reason the output its generating does not seem to change with either changing inverting or non inverting inputs. I mean, the output, remains same even when the non inverting input (+) is less...
  38. L

    Troubleshooting LT1394 Comparator Oscillation

    I have a LT1394 comparator in a circuit that I'm trying to troubleshoot. The problem is that once the variable voltage approaches the reference, just before a switch, the output signal oscillates between LO and HI. I haven't been able to dive too deeply into it, to figure out if its noise...
  39. A

    Replacing LM324 Op-Amp with LM339 Comparator

    hello guys I'm working on a line follower robot and i built following circuit(with the help of members in this forum :smile:) as line sensor. https://www.physicsforums.com/attachment.php?attachmentid=20782&stc=1&d=1254182755" it uses LM324 opamp as a comparator and RED LED as a sensor...
  40. S

    Using a MOSFET and comparator together as a switch

    Hello all, I was advised to use a MOSFET and a comparator together in a solar charger that I am building to stop the solar panel from charging the batteries when full. Seems logical, right? The only problem is I've never used MOSFETs or comparators, so I'm not really sure how to. I need a...
  41. H

    Can Slew Rate Limiting Cause Triangle Wave Output in Op-Amp Comparators?

    Hi, I'm sorry I can't follow the recommended structure for this, as it's not a problem as such, more of a 'what should I have got?' I have to write up a lab report in which we were using Op-Amps as summing amplifiers, comparators and integrators. We used an open loop 741 as the comparator...
  42. K

    How does a voltage comparator work? very simple explanation I need

    Hello every1.. I would like just sum help in unerstanding how a voltage comparator works.. I tried to read journals.. books.. but till now, I feel so lost.. can someone just give me a simple explanation of the SIMPLEST voltage comparator? sumthing to help me get on with it... I'd appreciate...
  43. Z

    LM339 comparator as solar panel switch

    Hello folks, I have been trying to make a circuit that would light up an LED when a small solar panel develops a certain voltage. My LED does not light up no matter how I hard I think about the circuit design. I would appreciate any help and suggestions. Thanks to all.
  44. K

    Application of a frequency comparator in speed monitoring systems

    what is the application of a frequency comparator in speed monitoring systems/ speed radar? pls let me know the detailed circuitry of the same and its implementaion. also what is the basic block diagram of a speed monitoring system based on comparision of pulses?
  45. K

    Frequency Comparator: Design & PLC Elements in Speed Radar

    does anyone know a frequency comparator is designed? also what are the elements of programmable logic control in a speed radar?
  46. E

    Solving Window Comparator Circuit: What Could Be Wrong?

    http://img409.imageshack.us/img409/4825/sdfsbe9.jpg i am getting this error when i simulated the above circuit what could be wrong **** CIRCUIT DESCRIPTION ****************************************************************************** ** Creating circuit file...
  47. N

    How Can an Op-Amp Comparator Circuit Monitor Soil Moisture Levels?

    A botanical laboratory requires an op.amp. alarm circuit which will indicate when the soil in a plant pot is not moist enough. With the assistance of the in information below design such a circuit remembering to include suitable values for any resistors used. when two copper probe wires are...