With opamps & comparators datasheets I've seen, it was typical to show in absolute maximum ratings values such as:

$$V_{SUPPLY} (V_{DD} \; to \; V_{SS}): \quad 12V$$ $$V_{DIF\_IN} (V_{-IN} \; to \; V_{+IN} ) : \quad 10V$$

It was almost common sense that the input signals individually go like this as well:

$$V_{SS} - 0.1V \le V_{-IN} \le V_{DD} + 0.3V$$ $$V_{SS} - 0.1V \le V_{+IN} \le V_{DD} + 0.3V$$

(where the -0.1V & +0.3V are generous leeways given by the implementors, as much as exceeding rails go)

Yet it was hardly specifically ruled out that inputs should stay within the supply rails. Since it's difficult to imagine how to implement an amplifier package where the inputs are not bounded by any rails, I simply assumed that the inputs indeed are bounded (as the last 2 math expressions). The documenters of the datasheet was simply writing it in terms of brevity.

Yet now, I'm dealing with a circuit where it's convenient that \$V_{-IN} > V_{DD}\$ & \$V_{+IN} > V_{DD}\$ & \$V_{DIF\_IN} \ge V_{+IN} - V_{-IN} \ge 0\$. So could anyone clarify if there are some opamps/comparators that indeed only care about differential inputs & not if they exceed the rails?

  • \$\begingroup\$ If you want to build a difference amplifier circuit, then consider that these can have input common ranges exceeding the supply rails, even for regular op-amps. It's a result of the two input resistors dropping the excess voltage. \$\endgroup\$
    – tobalt
    Commented Apr 25 at 4:18

1 Answer 1


You seek an op-amp whose input common-mode range exceeds the supply rails. This is possible, and Linear Technology (LT) made a series of op-amps with this capability, they were known as "over-the-top". Now owned by Analog Devices, you can find their datasheets and app notes on the AD website, links below.

Beware that the input characteristics (and other parameters) change substantially when the input voltage go beyond the supply rails, as shown in this graph from the datasheet:

enter image description here

Datasheets LT6015

App note: https://www.analog.com/media/en/reference-design-documentation/design-notes/dn533f.pdf

  • 1
    \$\begingroup\$ Maxim made several too (now also owned by AD), and there are a few from TI like that too. It's not specifically an LT thing. There's a couple ways to do it. \$\endgroup\$
    – Hearth
    Commented Apr 25 at 3:16
  • 1
    \$\begingroup\$ Yes, the MAX4240 is one such beast, it has the same issue: input bias current changes substantially when the input exceeds the supply rails. I think their marketing term was "beyond the rails". Several "current-sense" op-amps have high common-mode above one rail or the other, but not both, depending on whether they are intended to sense the Vdrop across a current-sense resistor that is in the positive line or the negative line. Cheers. \$\endgroup\$ Commented Apr 25 at 3:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.