# What is meant by “zerø-crossover” in the OPAx365 datasheet? And why the “ø”?

TI's OPAx365 seems to be a fairly ordinary op-amp after you dig through all the marketing buzzwords. But one thing sticks out: the datasheet repeatedly mentions having a "zerø-crossover" topology.

I initially thought the use of ø instead of o was a typo, but it doesn't seem to be as the term is used, including the ø, repeatedly throughout the datasheet. Is this some form of branding for their proprietary technology, or is there some actual reason for this spelling?

• @CL. This answers what a zero-crossover amplifier is, but it doesn't explain the use of ø, which is the main thing I was asking about. – Hearth Feb 12 at 15:19
• The phase symbol is marketspeak that engineers will hopefully enjoy. (low distortion = low phase noise at crossover). – Peter Smith Feb 12 at 15:20
• Empty sets and what marketing does to technical meaning are correlated, after all. – TimWescott Feb 12 at 15:58
• Wow, that's silly, especially when you're from a country that can pronounce it. Ø is not "a funny looking o", it's a completely different letter and sound. – pipe Feb 12 at 16:03
• @pipe I'm glad I'm not the only one who feels that way! – Hearth Feb 12 at 16:09

The term "zerø-crossover" is a TI marketing term for their solution to achieving a rail-rail input common-mode range. See the Functional Block Diagram from the TI datasheet:

In many rail-rail input CMOS op-amps, 2 pairs of input differential pairs (NMOS/PMOS) are employed to achieve a rail-rail input common-mode range. The drawback of this solution is that, each diff pair NMOS/PMOS has its own unique input offset voltage. So transitioning between using the NMOS to PMOS input differential pair results in cross-over distortion (variation of input offset voltage).

Of course you can design your amplifier in an inverting topology and the common-mode bias remains essentially constant. In that case you wouldn't suffer this form of cross-over distortion.

EDIT: Why the null symbol?

If I had give an honest guess, it would be TI trying to secure a trademark.

But, It is more than likely the design staff being clever.

In the opamp world, the act of removing the input offset voltage is referred to as nulling the amplifier. You can look all the way back to the 741, to find null terminals to allow the amplifier to be nulled in circuit. The use of the null symbol ø versus the letter o, would be a clever play on this terminology.

The MCP600x is a jellybean CMOS RRIO opamp which has this undesired behavior, as can be seen in the figure below:

Taken from the MCP600X datasheet.

• This answers the question very well except for one thing: I didn't quite make it clear, and that's my fault, not yours, but one of the main things I wanted to know was why the ø instead of o. I've clarified that in the title, and I think if you edit this answer to address that small detail it'd probably be the one I'm more inclined to accept, as it has much more information than the other one about what exactly this feature does, which is itself probably more valuable than knowing why they stuck a particular glyph in the name. – Hearth Feb 12 at 21:16
• @Hearth Answer updated, to what I believe to be the case. – sstobbe Feb 12 at 23:19
• alright, thank you! That's enough to get my upvote; I'm giving it a while before I accept an answer though. I like to give it 24 hours. – Hearth Feb 12 at 23:35

TI is not the only manufacturer with opamps that increase their common-mode range with a charge pump. What makes the OPA365 proprietary is the low-ripple charge pump (TI has patents on that, and uses apparently similar technology in the TPS6024x chips).

TI does not say how much this improves the opamp, or if this technology is just a more efficient way to get the same ripple. So for practical purposes, you can treat the ø symbol as a marketing affectation.