# Most Precise Voltage Comparator Available?

Discussion in 'Datasheets, Manuals and Component Identification' started by Johnyradio, Oct 30, 2012.

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Oct 30, 2012
Hello, what are the most precise voltage comparators on the market today?

Meaning, able to detect the tiniest differences between two input voltages.

Thanks

2. ### Harald KappModeratorModerator

10,771
2,427
Nov 17, 2011
How tiny? Millivolts, microvolts, Nanovolts?
How fast?
What range of input voltages?

Google "precision comparator" and you will find many hits, Each type of comparator being a bit different from the other, each designed for specific applications in mind.

Harald

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Oct 30, 2012
It's all relative, right? Precision has to be stated not in volts, but relative to 100% voltage swing, correct? It should be a percent, or ppm, or, for my purpose, the number of discreet "steps" that are detectable in the full swing.

Speed is not important.

I would expect I can scale my input up or down to fit the range of the comparator, right? So that should not affect the precision of the device.

Exactly. That's the problem.

4. ### CocaCola

3,635
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Apr 7, 2012
The lower the voltage resolution the more steps is will resolve to for any swing... Yes, it's relative but also fixed if the swing is fixed...

5. ### Harald KappModeratorModerator

10,771
2,427
Nov 17, 2011
In your original post you stated:
A difference of voltages is expressed in Volts, not percent. If you want a relative number, you have to put the the input voltage difference in relation to another voltage. This could be full range input voltage, it could also be the operating voltage of the comparator or any arbitrary reference voltage.

Having said that: What exactly is the requirement? You still haven't told us that. We could name any comparator that is in our view precise but still wouldn't fit your expectations.
From your using the expression "steps" one could assume that your are going into the direction of an analog-digital-converter. Then a good starting point would be the resolution of this adc and the absolute voltages involved. From that you could get the voltage equivalent to one LSB and this could be an anchor in the search for a suitable comparator.

Better yet: Tell us what you want to accomplish. There is often more than one way to achieve that goal.

Harald

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Oct 30, 2012
What do you mean "fixed"?
How can the swing not be fixed?
How can resolution not be fixed?

Thanks

7. ### Harald KappModeratorModerator

10,771
2,427
Nov 17, 2011
Swing is the difference between max. and min. input voltage. If your circuit operates from 3.3V this can ba vastly different from a circuit that operates from 12V.

Resolution is a measure of the minimúm change in signal that you can distinguish with your circuit.

An example:
circuit 1: Max. DeltaV=2V, 8 bit ADC
circuit 2: Max. DeltaV=2V, 12 bit ADC
circuit 3: Max. DeltaV=10V, 8 bit ADC
circuit 4: Max. DeltaV=10V, 12 bit ADC

Circuit 1 has a resolution of 8 bit = 1/256. With respect to DeltaV=2V this makes 1LSB=7.8mV.
Circuit 2 has a resolution of 12 bit = 1/4096. With respect to DeltaV=2V this makes 1LSB=0.488mV.
Circuit 3 has a resolution of 8 bit = 1/256. With respect to DeltaV=10V this makes 1LSB=39mV.
Circuit 4 has a resolution of 12 bit = 1/4096. With respect to DeltaV=10V this makes 1LSB=2.44mV.
You can easily see that resolution is not fixed. " variables (DeltaV, Number of Bits) were changed resulting in 4 different resolutions.

I think it would be really helpful you know your application so we can resolve the knot.

Harald

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Oct 30, 2012
"If you want a relative number, you have to put the the input voltage difference in relation to another voltage."
I may be incorrect, but I believe resolution or precision of comparators on data sheets is given in relative terms, not absolute volts. Is that incorrect?

"We could name any comparator that is in our view precise"
I am asking for the MOST precise comparators available. Are you saying that's a matter of opinion? Of course there are trade offs. I mentioned speed is not a factor.

I can scale my input up or down to fit the range of the comparator, right? So that should not affect the precision of the device. Is that an incorrect statement?

I am inventing something, so prefer not to share the details of my project. I'm not looking for circuit help or help with my design, but thanks for offering.

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Oct 30, 2012
I understand all of that. But you're saying that resolution or precision of a comparator is stated in absolute volts, and that seems incorrect to me.

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Oct 30, 2012
I think that's incorrect. In a given circuit the swing is fixed. True, another circuit may have a different swing, as you described. But In a given circuit the swing is fixed.

11. ### shrtrnd

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Jan 15, 2010
Burr Brown made some of the best circuits I've run across.
They were bought-out by Texas Instruments, who dropped a lot of the Burr Brown line.
But TI still sells some of the most popular Burr Brown line.
I'd check TI for Burr Brown comparators.
If there's somebody out there making better commercail stuff, I don't know who it is.