Any reason to choose TTL gates over CMOS ?

Thread Starter

2Hexornot2Hex

Joined Apr 16, 2020
29
Hi Gurus,

TTL/CMOS related questions are typical to newcomers to this hobby.
So here's another one :)
When I started (as a hobby), not a long time ago, I was discouraged going 'CMOS style' because of all the ESD warnings and the described precautions that should be taken while 'CMOSing'. So I went TTL... bought some gates....started working on something (of course some literature was also involved in a learning curve)
For the last couple of days, after reading more regarding ESD and how people actually work with CMOS (at home...not THAT much cautious...and all works fine) - I understand that all this "ESD handling" is not that difficult (in home/hobby environment) - so I ask myself - "Why wouldn't I switch to CMOS (wider Vcc range, more fanouts...) ?"

If the ESD handling factor is out of consideration, is there any reason why would someone go TTL (for a new projects), and not CMOS ?

Thanks.
 

joeyd999

Joined Jun 6, 2011
4,394
Hi Gurus,

TTL/CMOS related questions are typical to newcomers to this hobby.
So here's another one :)
When I started (as a hobby), not a long time ago, I was discouraged going 'CMOS style' because of all the ESD warnings and the described precautions that should be taken while 'CMOSing'. So I went TTL... bought some gates....started working on something (of course some literature was also involved in a learning curve)
For the last couple of days, after reading more regarding ESD and how people actually work with CMOS (at home...not THAT much cautious...and all works fine) - I understand that all this "ESD handling" is not that difficult (in home/hobby environment) - so I ask myself - "Why wouldn't I switch to CMOS (wider Vcc range, more fanouts...) ?"

If the ESD handling factor is out of consideration, is there any reason why would someone go TTL (for a new projects), and not CMOS ?

Thanks.
TTL is pretty much dead as a logic family for new designs -- and has been for quite some time.

And, if you get into microcontrollers and modern mixed signal chips, CMOS is your only option.
 

WBahn

Joined Mar 31, 2012
25,765
Hi Gurus,

TTL/CMOS related questions are typical to newcomers to this hobby.
So here's another one :)
When I started (as a hobby), not a long time ago, I was discouraged going 'CMOS style' because of all the ESD warnings and the described precautions that should be taken while 'CMOSing'. So I went TTL... bought some gates....started working on something (of course some literature was also involved in a learning curve)
For the last couple of days, after reading more regarding ESD and how people actually work with CMOS (at home...not THAT much cautious...and all works fine) - I understand that all this "ESD handling" is not that difficult (in home/hobby environment) - so I ask myself - "Why wouldn't I switch to CMOS (wider Vcc range, more fanouts...) ?"

If the ESD handling factor is out of consideration, is there any reason why would someone go TTL (for a new projects), and not CMOS ?

Thanks.
When CMOS gates first came out, they were extremely ESD sensitive. I've been involved with the designs of a couple chips that had a couple of pads that had no protection (because the lunatic fringe nature of the design could barely tolerate the capacitance of the bare metal pad to the substrate) and those chips had to be handled with extreme caution, and even then we fried some of them.

But over time we've developed very well-proven ways of protecting CMOS circuitry via pad-protection topologies. So now when you zap a chip, you are more likely to just make it less reliable and shorten its life expectancy rather than cause an immediate failure.

There are so many variants of either technology that it's hard to make sweeping statements, but standard TTL generally has greater driving capability that standard CMOS, so it can be easier to drive light loads with it that would stall CMOS. But there are plenty of high-drive CMOS families out there, two. But unless you have a specific reason to use TTL, such as being compatible with an existing design (and even that is negotiable), you should probably consider some form of CMOS as your go-to option.
 

dl324

Joined Mar 30, 2015
10,758
If the ESD handling factor is out of consideration, is there any reason why would someone go TTL (for a new projects), and not CMOS ?
There are more reasons why you wouldn't go with TTL. Price and availability being high on the list.

I've read anecdotes about TTL being static sensitive. Never experienced it first hand though.
 

OBW0549

Joined Mar 2, 2015
3,408
If the ESD handling factor is out of consideration, is there any reason why would someone go TTL (for a new projects), and not CMOS ?
I can think of only two:
  1. You simply MUST have a particular logic function, and it's available in one or more of the TTL variants but not in any CMOS variant; or
  2. You need extreme speed, making 74ASxxx the only way to go.
I can't think of any other reason why you'd want to use TTL. I haven't used any TTL variant in close to 40 years.

And for what it's worth, ESD sensitivity is no longer a big issue. It was, back in the early days of CD4000-series logic, but modern CMOS parts are pretty tough.
 
Last edited:

crutschow

Joined Mar 14, 2008
24,980
The CD4000 series is likely more robust than the 74xx CMOS higher-speed variants since it is built with an old process than has a thicker gate oxide.
 

Thread Starter

2Hexornot2Hex

Joined Apr 16, 2020
29
Can you advice which CMOS sub-family to choose to go to ? (in my case, of course)
I'm a beginner and high-speed circuits are currently non of a concern to me.
Some CMOS series are up-to 15V and some around 5V...it would be good to be covered by a broader voltage possible.
My current/near-future projects are intended to work with a power cord, but also battery operated would be built.

I got a suggestion on CD4000
I'm a beginner. Playing mostly with those CD4000 series ICs right now and I haven't lost one yet to ESD. Give them a try!
 

MrChips

Joined Oct 2, 2009
21,143
No particular reason except:

1) 74HC series is faster
2) 74HC series has a larger selection of functions
3) CD4000 series will most likely be discontinued before 74HC series.
 

Audioguru again

Joined Oct 21, 2019
1,503
RTL logic ICs were invented in 1962. I never saw anything using them.
DTL logic ICs were also invented in 1962. Products in my job used them and I learned about logic with them.
TTL logic ICs were invented in 1964 and I used them in my job and hobby for about 8 years.
Cmos CD4xxx logic ICs were invented in 1970 but I switched to using them in 1975 and never used the older logic families again.

I could not find out when 74HCxxx logic was invented. Sometime between 1978 and 1985 I began using them sometimes when I needed high speed or a high output current when using a 2V to 5V supply.
 
Top