Electronic – improve serial data signal using reversed output on a twisted pair

communicationlineserialtwisted-pair

This is a serial data communication with one or several transmitters and one or several receivers.

From the transmitter I have one serial data output (D+) and a second, reversed serial data output (D-).

On D+ "1" is 5V, "0" is 0V.

On D- "1" is 0V, "0" is 5V.

Both line will be output by a 3-state buffer of this type:
http://www.ti.com/lit/ds/symlink/sn74lvc2g241.pdf

On the receiver side, I need to use D- (the reversed signal) but it doesn't cost me anything to use D+ and an inverter schmitt trigger ("NOT1" on the schematic) because I plan to use a shcmitt trigger anyway.
I think it's better to use the standard signal for compatibility, if someone else wants to connect its own system to the receiver.

D+ and D- will be carried on a twisted pair of a CAT5 or 6 cable. As far as I know, this helps reducing noise and interference.

The question is: If I use the D+ line, can I do something with the D- line to improve the signal on the receiver?

Is using the D- line as in this schematic would make any sens? Or should I leave the D- line unconnected? Suggestion?

The goal is the to be able a cable as long as possible (100 or 200 meters for example) and as many nodes as possible (10, 20 etc). There is no requirement. Just making the best.
Imagine that there can be several identical receivers. (not visible on the schematic) and several transmitters too.

The resistors and the zener diodes are there for elementary protection.

Speed can be low or very low. As low as I want. It's synchrone communication.

This is still in development.

schematic

simulate this circuit – Schematic created using CircuitLab

Edito:
The idea would be this:
enter image description here

Best Answer

D+ and D- will be carried on a twisted pair of a CAT5 or 6 cable. As far as I know, this helps reducing noise and interference.

This only helps if: -

  • The sending end (transmitter) has a balanced (and optimally a differential) driver output
  • The receiving end has a balanced linear receiver that is capable of subtracting the analogue version of D+ from the analogue version of D-

The question is: If I use the D+ line, can I do something with the D- line to improve the signal on the receiver?

You feed both D+ and D- into a proper balanced and differential linear amplifier and use it's output (possibly with some gain but at least one comparator), to reconstruct your digital signal: -

enter image description here

The goal is the to be able a cable as long as possible (100 or 200 meters for example) and as many nodes as possible (10, 20 etc). There is no requirement. Just making the best. Imagine that there can be several identical receivers. (not visible on the schematic) and several transmitters too.

In addition to what I've already said, you may need termination resistors. If I were you I'd use RS485 interface chips. They are cheap and will do what you need i.e. the important thing you haven't yet considered functionally is how to disable more than 1 transmitters so that only one is allowed to drive the line at any one time.

So the best would be to twist the data wire with a ground wire?

See this and note the balanced drive impedances, \$R_S\$: -

enter image description here