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CD4093 question

LuckyDevil

Feb 19, 2017
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Hi,
After reviewing the data sheet and studying different schematics of various circuits that use the CD4093 I see a common occurrence that I can't seem to word properly to get any kind of answer from a search engine. I'm sure for many it's an elementary question. I'm trying to learn something. The CD4093 is a Quad Schmitt trigger. My understanding is that it has 4 triggers. Practically all of the circuits I look at that uses this IC are wired in such a way as to go into one , out and back into another. My question is why go through 3 times? Smoothing or filtering?
I'm going to try to upload an image.

Thanks
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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The 4093 is a quad 2 input nand gate.

It contains 4 separate gates, each having 2 inputs. These inputs have Schmitt triggers to condition the signals applied to them
 

LuckyDevil

Feb 19, 2017
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Thanks Steve but that didn't really address my original question. Anybody else?
 

OBW0549

Jul 5, 2016
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Practically all of the circuits I look at that uses this IC are wired in such a way as to go into one , out and back into another. My question is why go through 3 times? Smoothing or filtering?
The only person who could possibly answer that question is the person who designed this oddball, non-standard hack of a circuit.

There is nothing magical or mysterious about the CD4093 itself; as @(*steve*) indicated, it's just a plain, ordinary quad 2-input NAND gate with Schmitt trigger inputs and is normally used in digital logic the same as any other quad 2-input NAND gate.

But people sometimes do some pretty screwy things with CMOS, and use logic chips for quasi-logical purposes; in this circuit, as best I can tell, the intent for some unknown reason is probably for IC4A and IC4D to each produce a brief positive-going pulse (a short one on IC4A, and a longer one on IC4D) when the output of IC4C goes low. IC4B apparently does nothing at all. Neither "smoothing" nor "filtering" has anything to do with whatever is going on here.
 

(*steve*)

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I tried to answer what seems to be your misunderstanding. The are 8 Schmitt triggers in that package.

That particular circuit has several RC delays which will convert a rising edge into a negative going pulse. Note that of the 4 gates shown, three are being used as Schmitt trigger inverters, and the fourth we don't know because the diagram is clipped.

This is one one of my favorite bugbears. Why do designers use this gate instead of a hex inverting Schmitt trigger when all they want is an inverter?
 

(*steve*)

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IC4B apparently does nothing at all.

It produces a negative going pulse at the end of the negative going pulse produced by the preceding gate.

Schmitt trigger inverters can be used for all sorts of magic involving the creation of pulses at level changes, extending pulses, etc. They are wonderfully versatile.
 
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LuckyDevil

Feb 19, 2017
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"The only person who could possibly answer that question is the person who designed this oddball, non-standard hack of a circuit."

An ironic observation ( or opinion) since the person and company that designed that " oddball, non-standard hack of a circuit" has actually made a fortune from that completed circuit. It's quite possible they are too busy actually designing than to be hanging around an "oddball" forum .
Since I looked and couldn't find the "delete account" button, maybe Steve can make his self useful and remove me and my info from this "oddball" forum.
 

OBW0549

Jul 5, 2016
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It produces a negative going pulse at the end of the negative going pulse produced by the preceding gate.
What preceding gate? It's not connected to any other part of the circuit, other than ground and +5V, and is just sitting there with both its inputs high and its output low.
 

(*steve*)

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Ic4b's input is connected to the output of ic4d's output via a capacitor.

Are we looking at the same circuit?
 

(*steve*)

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Since I looked and couldn't find the "delete account" button, maybe Steve can make his self useful and remove me and my info from this "oddball" forum

No, because I don't want to hide your bad attitude.
 
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