Comparator with constant offset
Comparator with constant offset
(OP)
I'm working with two voltage levels where I need a comparator to switch when the difference between the two pass 100 mV.
Problem is, the common-mode voltage varies, so I can't make the offset between the two inputs using resistors.
One voltage is DC, the other is 16 kHz pulses.
Can anyone point me in the right direction?
Do comparators exist with built-in constant offset?
Or can you suggest a different way of "injecting" 100 mV into one input?
BTW, supply voltage is 12 V, the signal is somewhere in between.
Thanks,
Benta.
Problem is, the common-mode voltage varies, so I can't make the offset between the two inputs using resistors.
One voltage is DC, the other is 16 kHz pulses.
Can anyone point me in the right direction?
Do comparators exist with built-in constant offset?
Or can you suggest a different way of "injecting" 100 mV into one input?
BTW, supply voltage is 12 V, the signal is somewhere in between.
Thanks,
Benta.





RE: Comparator with constant offset
Is that difference in both directions? In other words, 100mV of hysteresis? If so, then easy (?).
RE: Comparator with constant offset
But it must be the heat affecting me...
A summing amplifier before the DC input to the comparator can of course add the 100 mV offset.
As usual, this came to my mind when driving home from work (emptying your brain suddenly brings solutions, which is why it's important to take a 5...10 min break regularly).
Thanks for replying, sorry I wasted your time.
Cheers,
Benta.
RE: Comparator with constant offset
RE: Comparator with constant offset
Keith Cress
kcress - http://www.flaminsystems.com
RE: Comparator with constant offset
No, the problem is exactly the varying common-mode voltage. None of the inputs are ground or positive referenced.
Anyway, I've solved it now.
Cheers,
Benta
RE: Comparator with constant offset
Depending on the application, another way to do this is by intentionally unbalancing the input. For example the LM311 comparator has two balance inputs which can vary the input offset over a modest range.