Hi people...
Since we were talking of logic levels... i thought
this would be a nice anecdote to add on..
I wrote to one of the authors of the digital design
books we use as text in college..
on why 5v was choosen as logic one...
this is what he has to say..
PS please read the linked essay
Anurag
----- Original Message -----
From: Anurag Chugh
To: John F. Wakerly
Sent: Thursday, January 06, 2005 4:49 AM
Subject: Re: Why +5V?
Dear Sir,
Dear Sir,
I am a student of electronics engineering currently
in third year of my four year course. Although I am done with Digital Design
Course and should have asked this question then but it never struck me then!
Just have been taking things as they were told to me. But now that I am trying
my luck by constructing all sorts of circuits, (microcontroller, digital, analog
et al) I find my self asking this Question : Why 5 Volts? why not any other
level for logic 1.
I tried your book but i couldnt find the answer. Maybe I didnt search well
but still I suppose there is a bit of history there if there is no reason behind
it.. after all if not 5Volt then what else could it be 6 or 7 ?
It had to be something and i sure would like to
know if there was any reason for it!. I used your book during the courses called
Digital Design I and Digital Design II. I have never found any other author
write so passionately and in so much completeness as yourself and so I thank you
very much for making my DD courses real enlightening and enriching experience.
Looking forward to your reply
Thanking you
Yours Faithfully
Anurag Chugh
Third Year (Electronics Engineering)
Vivekananda Education Society's Institute of
Technology (Affiliated to Mumbai University),
Chembur, Mumbai (Bombay) - 400071
India
PS:
Our course didnt require us to know how the gates
were actually implemented, so i conveniently bunked Digital Circuits chapter
when studying thoroughly for exams but I had an overview of it and I couldnt
find the answer to my question there. I wonder if many other students have asked
you the same question before?
From: John F. Wakerly
To: Anurag Chugh
Sent: Thursday, January 06, 2005 4:49 AM
Subject: Re: Why +5V?
This was the voltage chosen for the original TTL family. I'm not sure
of the exact reason. It's possible that some previous logic families used
5V, but then there would still be the question for that family. It was
undoubtedly a tradeoff between power consumption, reliable switching operation,
and noise margins.
Or perhaps it's more like the reason that railroad tracks are separated by the width that they are (see www.naciente.com/essay94.htm).
John
Or perhaps it's more like the reason that railroad tracks are separated by the width that they are (see www.naciente.com/essay94.htm).
John