No True Digital Realm?

I have excerpted a piece of correspondence from a friend here. Hope it makes for lively discussion.

"The particular application was understanding why digital computers

and any digital circuit only has ones and zeroes. A typical integrated

circuit works on 5 volt logic. A lot of people think that a 1 is +5 volts

while a 0 is 0 volts. If this were the case, nothing would ever work

reliably since the slightest voltage drop would be interpreted as in between

a 1 and a 0 which is not allowed. So, the designers set a threshold voltage

about 1/2 way in between or about 2.5 volts. This means that the decision to

decide if an input to an IC is to be interpreted as a 1 is made when the

voltage is between 2.5 and 5.0 while the decision for a 0 is between 0 and

2.5. It's obvious that, if the voltage, or noise on the input, is around 2.5

volts (even for an instant), the circuit could see a series of 1s and 0s

which of course is no good. Other designs then chose to have a 1 represented

by a voltage between 4 and 5 volts while a 0 would be between 0 and 1 volt.

This meant that the range between 1 and 4 volts did not change the status

detected and is called "noise immunity". Of course, if the voltage was about

1.1 volts, it probably would not be interpreted as a 0 but would not be a 1.

The same thing goes for everything else! Answers to questions such as "What

time is it?", "How do you feel?", "Is that heavy?", "How much does it

weigh?", "How old are you?", "Which direction is North?", and on and on.

I started telling everyone who would listen (ha!) that "there is NO digital

world, only analog".

Reply to
Long Ranger
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Maybe. Maybe when we see down to the finest of quantum details we will find there is no analog world, only digital.

Reply to
operator jay

: > "The particular application was understanding why digital computers : >

: > and any digital circuit only has ones and zeroes. A typical integrated : >

: > circuit works on 5 volt logic. A lot of people think that a 1 is +5 volts : >

: > while a 0 is 0 volts. If this were the case, nothing would ever work : >

: > reliably since the slightest voltage drop would be interpreted as in : between : >

: > a 1 and a 0 which is not allowed. So, the designers set a threshold : voltage : >

: > about 1/2 way in between or about 2.5 volts. This means that the decision : to : >

: > decide if an input to an IC is to be interpreted as a 1 is made when the : >

: > voltage is between 2.5 and 5.0 while the decision for a 0 is between 0 and : >

: > 2.5. It's obvious that, if the voltage, or noise on the input, is around : 2.5 : >

: > volts (even for an instant), the circuit could see a series of 1s and 0s : >

: > which of course is no good. Other designs then chose to have a 1 : represented : >

: > by a voltage between 4 and 5 volts while a 0 would be between

0 and 1 : volt. : >

: > This meant that the range between 1 and 4 volts did not change the status : >

: > detected and is called "noise immunity". Of course, if the voltage was : about : >

: > 1.1 volts, it probably would not be interpreted as a 0 but would not be a : 1. : >

: > The same thing goes for everything else! Answers to questions such as : "What : >

: > time is it?", "How do you feel?", "Is that heavy?", "How much does it : >

: > weigh?", "How old are you?", "Which direction is North?", and on and on. : >

: > I started telling everyone who would listen (ha!) that "there is NO : digital : >

: > world, only analog". : >

: >

: : Maybe. Maybe when we see down to the finest of quantum details we will find : there is no analog world, only digital. : : And the politically incorrect masters of the world will come up with a new field of physics to describe it all.

Seriously though, there are more than two states to the digital world. There is the tri state, for one: +V, -V, and 0V. Then you have the multi-states used in modems and the like; several stairstepped states there. Digital simply means "digits all", not that there are only two states. It's based on the interpretation of "digits", not an almost infinite set of levels over a range; therefore, it is digital, because it encompasses a set number of digits, not the infinite possibilities of the analog segment.

Huh?

Pop ;-]

Reply to
Pop

Paul Revere started the whole thing: "One if by land, two if by sea." He didn't know how to send a zero!

Reply to
VWWall

Digital is an interpretation of an analog signal so that the result can only take on a finite number of states. In the practical world, all signals are analog (capable of having an infinite number of states, or close to it) while digital signals interpret that infinite number of states into a finite number number of states. That leads to some error when doing analog to digital conversion (quantizing noise) and a range of signal levels being interpreted as a single digital state for digital signals. Note that digital signals also require a timing element to avoid transitional effects.

The advantage of digital is that, using regenerators appropriately, there is no (or virtually none, depending on how often you use regenerators) cummulative noise in transmission. The penalty is quantizing noise in A to D conversions.

For all intents and purposes, the world is analog but we can interpret analog signals in a digital fashion. Since the world is subject to interpretation, I guess that means that there is a digital world.... ;>)

E. Tappert

PS - a mere re-interpretation of Paul Revere's signal allows for "one if by land (interpret as a binary zero) and two if by sea (interpret as a binary one)" Alternatively, we can think of his signal as a three state digital signal, "one if by land, two if by sea, and no lantern means I don't know!" One the other hand, digital signals don't have to include a "zero" at all... Let's kill this line of thought before it gets out of hand...

Reply to
Eric Tappert

That is why schmitt trigger digital circuits have positive feedback. As soon as it thinks it is time to turn on or off it feeds back some of the signal to slam it over. Actually when you look at the spec it will say a zero is around 0-1v and a one is 4-5v. The region in between is not a valid state. There are rise time specs that define the time it can be in the invalid state while switching and if the designer can't insure that he uses a schmitt trigger that will use the feedback deal to flip the circuit on the rise.

Most digital circuits are also clocked so they don't pay attention to the switching time. They only look when things settle down.

Reply to
gfretwell

'Tis true. Planck mass (~2.2E-8kg) Plank length (~1E-35M) and Planck time (~5.4E-44s) are the quanta. More hasn't quite gotten us there yet. ;-)

Reply to
Keith Williams

An often ignored fact is that the telegraph used relays to re-generate the signal. This allowed for trans-continental transmission over noisy lines. It's interesting that Morse also used the statistical properties of the English language in his "code". Not as good as Hoffman or Shannon, but predating them by a bit! :-)

We can approximate the analog world to whatever degree of accuracy is required. One real advantage of the digital "world" is that we can chose among "accuracy", "bandwidth", and "noise immunity". In addition we can more easily use the statistical properties of the "real world" to optimize any of the above.

Agreed! :-) I should have put: :-) after "He didn't know how to send a zero." I don't think he was using nrz data, however. ;-)

Reply to
VWWall

The basic question should be: is the universe discrete? I believe it is, because quanta do exist and so far nobody has found evidence of fraction of quanta. Thus the universe at its core is digital. Gene

Reply to
EpsilonRho

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