millivots differentail input voltages op-amps

Thread Starter

dar2525

Joined Jun 17, 2005
21
I am trying to observe the output of a comparator for small differential input voltages of -3mV to 3mV. I want to verify how accurate my comparators are.

I tried using a power supply, by setting the non-inverting to 2.5V and adjusting the inverting until I measure a voltage difference of millivolts, but the measurments are not steady. I probally will need a more precision voltage supply for this.

I was thinking of using potentiometers to adjust the non-inverting and inverting inputs until I get stable differential input millivolts. Will this work? Have anyone else tried this. I am using ALD2301A for my comparators.

Thanks in advance
 

Nik

Joined May 20, 2006
55
IMHO, you're into 'Kelvin Country'.

I reckon you'll need a discrete resistor ladder and a very stable voltage supply to precisely pick off the tiny steps you'll need...
 

Thread Starter

dar2525

Joined Jun 17, 2005
21
Originally posted by Nik@May 23 2006, 10:17 AM
IMHO, you're into 'Kelvin Country'.

I reckon you'll need a discrete resistor ladder and a very stable voltage supply to precisely pick off the tiny steps you'll need...
[post=17299]Quoted post[/post]​
Thanks. I can adjust my voltage supply to 5V. I think I will try some very precise potentiometers
 

n9352527

Joined Oct 14, 2005
1,198
Originally posted by dar2525@May 23 2006, 05:33 PM
Thanks. I can adjust my voltage supply to 5V. I think I will try some very precise potentiometers
[post=17309]Quoted post[/post]​
Maybe a 10 turns pot? And something to get rid of the noise. Not really worth the trouble IMHO or the cost.
 

Thread Starter

dar2525

Joined Jun 17, 2005
21
Originally posted by n9352527@May 23 2006, 03:11 PM
Maybe a 10 turns pot? And something to get rid of the noise. Not really worth the trouble IMHO or the cost.
[post=17311]Quoted post[/post]​

Thanks, what does IMHO mean?
 

Thread Starter

dar2525

Joined Jun 17, 2005
21
Originally posted by Ron H@May 23 2006, 08:02 PM
You can set this up as an op amp and let it measure its own offset voltage. See below.
[post=17313]Quoted post[/post]​

Thanks fpr replying. Will this be measuring the input or output offset voltages? Will the output be the offset voltages? Why is negative feedback needed? Can you please explain to the best of your ability why negative feedback is involved?

Thanks in advance
 

kubeek

Joined Sep 20, 2005
5,733
Originally posted by dar2525@May 25 2006, 01:42 PM
Thanks fpr replying. Will this be measuring the input or output offset voltages? Will the output be the offset voltages? Why is negative feedback needed? Can you please explain to the best of your ability why negative feedback is involved?

Thanks in advance
[post=17330]Quoted post[/post]​
It is connected as amplifier with gain -1000, so on the output is -1000*Voffset, becasue + and - inputs are on the same potential, so the opamp sees only the offset.
 

Ron H

Joined Apr 14, 2005
7,014
Originally posted by kubeek@May 25 2006, 09:06 AM
It is connected as amplifier with gain -1000, so on the output is -1000*Voffset, becasue + and - inputs are on the same potential, so the opamp sees only the offset.
[post=17332]Quoted post[/post]​
Thanks, kubeek. I've been out of town. To clarify - the output is equal to -1000*input_offset.
 
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