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Electronics/Why use inverter symbol in this circuit ?

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Question
In this article, http://www.edn.com/design/test-and-measurement/4391393/Single-hex-inverter-IC-ma,

http://m.eet.com/media/1168037/single-hex-inverter-ic-makes-four-test-gadgets-fi
A circuit is used to detect a user degined low logic level and high logic level, by lighting a red & green led. It uses an "inverter" that to me works just like a mosfet gate. Top inverter looks like a mosfet with red led at source, bottom inverter looks like mosfet with green led at drain.

Regardless, they do not function as inverter at all (inverting logic 0 & 1 ). Logic inverter takes input of 0 or 1. But in this case, looks like the gate to the "inverter" must be > threshold for it to work.

The use of inverter symbol confuses me. Why the need for it ?
THanks

Answer
It looks like an opamp to me.  Most opamps have two inputs; inverting and non-inverting. Here we are talking about the electrical version, not the soft inversion used in logic configs.

So, if the inverting input is used it means the output of the voltage swing is opposite from the input.

Hope this helps.  

Electronics

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Electronics questions about AC, DC and digital theory.

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Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

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IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

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BSEE University of North Dakota

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