Quad dual-input NOR WITH schmitt trigger 15V - Page 1
Forum section: electronics / projects

author: austnais
author_rank: Contributor
timestamp: April 01, 2016, 03:11:53 pm
content: Hi guys!Does this at all excist? The 4001 is capable of 15V, but doesn't have a schmitt trigger on the inputs. 74AHC02 has schmitt triggers, but only allows 5V operation.Am I really being to difficult? Any NANDs I've found does have schmitt.On a sidenote, why would anyone NOT put a schmitt trigger in? Is it something with cost?Thanks,,

author: MK14
author_rank: Super Contributor
timestamp: April 01, 2016, 03:15:27 pm
content: I'm NOT 100% clear, exactly what you are looking for.But here are some Schmitt triggered, NOR gates.http://www.ti.com/product/SN74HC7002

author: austnais
author_rank: Contributor
timestamp: April 01, 2016, 03:19:40 pm
content: Thanks, this is the right stuff, but it is only 5V operation max. I would need one that can work with 15V logic level. I know it's kind of weird, but a lot of the 4000-series can actually work on 15V and for speed-reasons I want to work on 15V.So if you have one for 15V I would be more than happy

author: MK14
author_rank: Super Contributor
timestamp: April 01, 2016, 04:00:16 pm
content: I don't think you can. If you can, I have not been able to find one.15V is growing out of fashion, and may become harder and harder to get, eventually.It seems they mainly catered for the inverters (7414's), adding or at the same time, doing Nands as well. Most of the rest of the standard gates seem to be free of Schmitt Triggering. (But some logic families have partial Schmitt Triggering on all inputs, apparently and some buffer chips may do it as well).Presumably proper Schmitt Triggering adds cost/difficulties/problems, making the IC manufacturers reluctant to use it on their full range. E.g. I can imagine that it would make it significantly harder to test them on the production line and specify them.I.e. testing costs money (equipment/time/hassle), and if it was tightly specified, it could increase the number of ICs, which would "fail" testing. Which would also cost money, as those chips would have to be rejected, rather than sold.Also I'm not sure, if adding it, causes a slight slowdown, on the fastest logic transitions, which would also be a disadvantage.

author: dacman
author_rank: Frequent Contributor
timestamp: April 01, 2016, 10:43:07 pm
content: A Quad NAND Schmitt Trigger could be configured as a single NOR.A Hex Schmitt Trigger could be used in front of a NOR.With two Hex Inverters and one Quad NAND, four NOR gates could be built.

author: MK14
author_rank: Super Contributor
timestamp: April 02, 2016, 05:23:27 am
content: Quote from: evb149 on April 02, 2016, 05:07:24 am+1 on your full reply!I'd MISSED that bit (speed), when I read through this thread. Well spotted!I thought/assumed, they needed 15V for some hardware reason, and were determined to just use a single IC.They (OP) have NOT described what they are trying to do, or what the hardware actually is, etc etc. Making solving their real problem, much harder on a forum.As you said, the original 4000 CMOS series is fairly slow, by today's standards.

author: technix
author_rank: Super Contributor
timestamp: April 02, 2016, 01:43:13 pm
content: If it is for interfacing existing circuitry (4004?) you can level shift from 15V to 5V using a resistive divider and shift up using Schottky diodes and pullup resistors.If it is a new design you can consolidate all your discrete logic into one or two CPLDs like Altera EPM240T100C5N's. Those are much faster than any discrete logic (including things like 74AHC) out there, and can consolidate a whole Eurocard worth of 7400-series (or 4000-series) into one single battery-power-friendly chip.