[SI-LIST] Re: Differential signaling history
- From: "Charles Hill" <chuckh@xxxxxxxxxxx>
- To: <xlzhou@xxxxxxxxx>, "'Ingraham, Andrew'" <Andrew.Ingraham@xxxxxx>
- Date: Wed, 5 Mar 2003 10:04:28 -0700
Mick,
The pioneers developing differential transmission in telephone circuits
understood the issues very well, resolved the problem very cleverly, and
made a major positive impact on social developments in the USA.
In the early 20th century, a large segment of the population of the US lived
in rural areas without rapid communication or electric power. Differential
signal transmission techniques allowed telephones to be installed long
distances from central offices (30 miles). This enhanced communication
brought isolated areas closer to the mainstream of American life, bringing
the country together. Their motivation was to further democracy. In the
times, there was a large progressive movement to benefit "the common
people". Another example was the large effort to provide rural
electrification.
I'm convinced the developers of differential transmission not only
understood the technical aspects, they understood the positive impact on the
country as a whole. They were just as smart and clever as we are (perhaps
more so), their technology was not as sophisticated.
We are on the verge of witnessing a similar process take place in many
countries with the advent of cellular telephone technology. This allows
communication in rural areas with a much smaller capital investment. The
most dramatic effects on the world are likely to come from cellular networks
in China.
Regards,
Chuck
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zhou, Xingling (Mick)
Sent: Wednesday, March 05, 2003 9:18 AM
To: 'Ingraham, Andrew'; Zhou, Xingling (Mick)
Cc: si-list
Subject: [SI-LIST] Re: Differential signaling history
I think we are in the right direction. Any documents would be helpful to
understand it. Did they resolve the issue right away ? Or any other failed
tries etc. ? May be reducing noise is the motivation, must be. But how (the
solution) is another problem) ? From our point of view, the reasons are not
more than explanations. Did the pioneers know the good "reasons" as we do ?
I doubt. A typical example is that Edison did know all the sciences/reasons
behind his great inventions in many cases.
Still rough thoughts. Fortunately, we can keep designing differential pairs
(even better) without knowing the history at all !
Mick
-----Original Message-----
From: Ingraham, Andrew [mailto:Andrew.Ingraham@xxxxxx]
Sent: Wednesday, March 05, 2003 10:46 AM
To: xlzhou@xxxxxxxxx
Cc: si-list
Subject: RE: [SI-LIST] Differential signaling history
For that, you probably need to go back to the beginnings of the telephone.
Perhaps even the telegraph.
Single-ended phone circuits over long distances with a common "ground"
simply don't work. Far too much noise.
You need two wires to complete a circuit, and if neither one is ground, you
logically get a differential pair.
They realized back then that the pairs had to be kept well balanced. On old
open wire telephone lines that used to run down highways or alongside train
tracks, you'd see that they periodically swapped the wires in each pair (at
prescribed intervals) to maintain balance and cancel coupling between all
the pairs and from other sources.
Regards,
Andy
> I am curious about the history of differential signaling. We can easily =
> explain in various versions intuitively or mathematically the benefits =
> of differential signaling now either in circuit design (differential =
> amplifiers/also called differential pair, for example) or in PCB design =
> (differential pairs), even in cable designs. What the first guys who =
> came up this idea originally thought and how/when they implemented the =
> idea ? etc.
>
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