---
title: What is the Purpose of the A not and B not Channels?
description: The A not and B not channels compliment the A and B channels to keep noise to a minimum.
---

<https://www.dynapar.com/faq>

# [What is the Purpose of the A not and B not Channels?](https://www.dynapar.com/faq/what-is-the-purpose-of-the-a-not-and-b-not-channels)

 Written by [London Rhodes](https://www.dynapar.com/faq/author/london-rhodes) | May 24, 2021 5:36:57 PM

The A not and B not channels are the compliments of the A and B channels. This means that when signal A is high, signal A not is low and when A is low, signal A not is high. The same is true for any signal that has a compliment. This is commonly used to keep noise to a minimum. Some input cards will accept both the A and A not signal. It then compares the two signals to help eliminate common mode noise that may have been picked up on the line. This is done by accepting a pulse only when signal A is high and signal A not is low. This is true for any channel that has a compliment, signal A was used only as an example. This is commonly called a Differential Output.

[View full post](https://www.dynapar.com/faq/what-is-the-purpose-of-the-a-not-and-b-not-channels)

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