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Home > Archive > Electrical Engineering > April 2006 > digital vs analog
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| Hello all.
I'm having an argument with a co-worker. I accept I could be totally
wrong.
The discussion, believe it or not, is about the nature of digital vs
analog signals.
My argument is that fundamentally "digital" in the context of "digital
vs analog" is a reference as to how information is represented in the
signal. Aside from that, a digital signal is fundamentally no
different than any analog signal at the "wave level." All the
fundamentals are still there, phase-lock, frequency-lock, attenuation,
impedance, etc. Effectively, at this level a the term digital is no
longer relevant and we are left dealing with traditional analog issues.
His argument is that a digital signal is fundamentally very different
than analog, and that a phase-lock on a digital signal is a totally
different beast than on an analog signal.
This conversation started because I argued that resetting a T1 CSU
after a power hit or rain storm (should it begin taking errors) could
be a valid fix if the errors cease, because a digital signal is
fundamentally no different than an analog signal when it comes to
signal propogation, synchronization, etc.
He argues that a T1 only breaks if a serviceable/replaceable component
is malfunctioning and must be replaced and the digital signals are not
subject to the same propogation issues as an analog signal. Resetting
the CSU only prolongs the detection and subsequent reparation of the
faulty component. The environmental factor only served to expose the
problem.
I acknowledge you can regenerate a digitally encoded signal easily as
opposed to an analog signal, but again this is only due to the
difference in how the information is represented.
Its a stupid argument. Nonetheless. I'm appealing to the masses for
support.
| |
| chuck 2006-04-22, 10:21 am |
| angry wrote:
> Hello all.
>
> I'm having an argument with a co-worker. I accept I could be totally
> wrong.
>
> The discussion, believe it or not, is about the nature of digital vs
> analog signals.
>
> My argument is that fundamentally "digital" in the context of "digital
> vs analog" is a reference as to how information is represented in the
> signal. Aside from that, a digital signal is fundamentally no
> different than any analog signal at the "wave level." All the
> fundamentals are still there, phase-lock, frequency-lock, attenuation,
> impedance, etc. Effectively, at this level a the term digital is no
> longer relevant and we are left dealing with traditional analog issues.
>
> His argument is that a digital signal is fundamentally very different
> than analog, and that a phase-lock on a digital signal is a totally
> different beast than on an analog signal.
>
> This conversation started because I argued that resetting a T1 CSU
> after a power hit or rain storm (should it begin taking errors) could
> be a valid fix if the errors cease, because a digital signal is
> fundamentally no different than an analog signal when it comes to
> signal propogation, synchronization, etc.
>
> He argues that a T1 only breaks if a serviceable/replaceable component
> is malfunctioning and must be replaced and the digital signals are not
> subject to the same propogation issues as an analog signal. Resetting
> the CSU only prolongs the detection and subsequent reparation of the
> faulty component. The environmental factor only served to expose the
> problem.
>
> I acknowledge you can regenerate a digitally encoded signal easily as
> opposed to an analog signal, but again this is only due to the
> difference in how the information is represented.
>
>
>
> Its a stupid argument. Nonetheless. I'm appealing to the masses for
> support.
>
Interesting discussion.
Surely at the level of Maxwell's equations, there is no distinction in
theory between analog and digital.
At the other extreme, say for a computer programmer dealing strictly
with binary circuits and operations, analog representations are not
likely to be needed. But for a digital circuit designer, the analog
nature of digital signals can be extremely important (i.e., Fourier
analysis).
So at the level of fundamental theory, I would say no difference. At the
level of application, I would say that appropriate (useful) modeling and
analytical tools for analog and digital signals would often be different.
Does that help?
Chuck
| |
| Floyd L. Davidson 2006-04-22, 11:21 am |
| "angry" <angry_engineer@yahoo.com> wrote:
>Hello all.
>
>I'm having an argument with a co-worker. I accept I could be totally
>wrong.
>
>The discussion, believe it or not, is about the nature of digital vs
>analog signals.
>
>My argument is that fundamentally "digital" in the context of "digital
>vs analog" is a reference as to how information is represented in the
>signal.
Absolutely correct. (I'll explicitly define that for you at the
end of this article, with an impeccable cite.)
>Aside from that, a digital signal is fundamentally no
>different than any analog signal at the "wave level." All the
>fundamentals are still there, phase-lock, frequency-lock, attenuation,
>impedance, etc. Effectively, at this level a the term digital is no
>longer relevant and we are left dealing with traditional analog issues.
True, though that might mean different things to different
people, so it's hard to be sure exactly what it is supposed to
be saying.
>His argument is that a digital signal is fundamentally very different
>than analog, and that a phase-lock on a digital signal is a totally
>different beast than on an analog signal.
The modulation process is analog, even if the modulating signal
is digital. Phase is an analog characteristic of a signal,
regardless of whether the signal carries digital information or
analog information. You can of course modulate the phase of a
signal with digital information. And one can have an analog
circuit that provides a phase lock to a signal that carries
digital information.
Note that virtually every T1 receiver in existence has a circuit
to recover the clock rate of the incoming digital signal. That
circuit is a phase locked loop. It is an *analog* circuit, in
all respects. (Not that a digital circuit could not be designed
to provide the clock rate, but it would be several times more
expensive.)
>This conversation started because I argued that resetting a T1 CSU
>after a power hit or rain storm (should it begin taking errors) could
>be a valid fix if the errors cease, because a digital signal is
>fundamentally no different than an analog signal when it comes to
>signal propogation, synchronization, etc.
True.
>He argues that a T1 only breaks if a serviceable/replaceable component
>is malfunctioning and must be replaced and the digital signals are not
>subject to the same propogation issues as an analog signal. Resetting
>the CSU only prolongs the detection and subsequent reparation of the
>faulty component. The environmental factor only served to expose the
>problem.
Ideally once an error condition is gone the hardware should be
able to synchronize itself to the signal and begin operating in
a normal manner. That doesn't always happen and it is always
an equipment fault when it doesn't.
The difference between your colleague's concept and reality is
that the malfunction can be a *design* malfunction, rather than
a component malfunction. The cause might be hardware
(insufficient surge protection, for example) or software (some
specific signal condition sends the software into an unbreakable
loop).
>I acknowledge you can regenerate a digitally encoded signal easily as
>opposed to an analog signal, but again this is only due to the
>difference in how the information is represented.
That is exactly true. But of course you do not want to under
emphasize the significance of that statement. Noise immunity is
the principal advantage of digital transmission systems. A
digital system will operate without error over a medium (e.g.,
fiber optics) that has far too much noise to use with analog
techniques. And because the signal can be precisely
regenerated, noise is not cumulative. Hence multiple sections
can be added in tandem to provide extremely long physical
circuit lengths, all with zero errors. Analog systems cannot do
that. Analog systems on the other hand can provide a higher
output signal to noise ratio while using less bandwidth.
>Its a stupid argument. Nonetheless. I'm appealing to the masses for
>support.
It isn't really such a stupid argument. It comes up quite often
as people migrate their concepts from an analog world to a
digital one. Some 25 years ago it was fairly difficult to find
telco people who had enough experience with digital facilities
to know much about it. Today of course there are people
retiring who have *always* worked with digital! And they can't
quite get a grip on how analog circuits work... :-)
Whatever, here are the killer definitions. These are from the
Telecommunications: Glossary of Telecommunication Terms, Federal
Standard 1037C at http://www.its.bldrdoc.gov/fs-1037/
ANALOG SIGNAL
1. A signal that has a continuous nature rather
than a pulsed or discrete nature. Note:
Electrical or physical analogies, such as
continuously varying voltages, frequencies, or
phases, may be used as analog signals
ANALOG DATA
Data represented by a physical quantity that is
considered to be continuously variable and has a
magnitude directly proportional to the data or
to a suitable function of the data.
ANALOG TRANSMISSION
Transmission of a continuously varying signal as
opposed to transmission of a discretely varying
signal.
DIGITAL
Characterized by discrete states.
(Note that I prefer a definition that also mentions a finite symbols set,
which is redundant information but makes the meaning much more obvious.)
DIGITAL DATA
1. Data represented by discrete values or
conditions, as opposed to analog data.
2. Discrete representations of quantized
values of variables, e.g. , the representation
of numbers by digits, perhaps with special
characters and the "space" character.
DIGITAL PHASE MODULATION
Modulation in which the instantaneous phase of
the modulated wave is shifted between a set of
predetermined discrete values in accordance with
the significant conditions of the modulating
signal.
SIGNAL
1. Detectable transmitted energy that can be
used to carry information. 2. A time-dependent
variation of a characteristic of a physical
phenomenon, used to convey information
MODULATION
The process, or result of the process, of
varying a characteristic of a carrier, in
accordance with an information-bearing signal.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| electrician@electrician2.com 2006-04-23, 3:21 am |
| <<The modulation process is analog, even if the modulating signal
is digital. Phase is an analog characteristic of a signal,
regardless of whether the signal carries digital information or
analog information. You can of course modulate the phase of a
signal with digital information. And one can have an analog
circuit that provides a phase lock to a signal that carries
digital information.[color=darkred]
What is a person with your knowledge doing living in Barrow, Alasak.
The world needs you Floyd.
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