What's differential here? Tying one line to ground makes single ended signaling.but the differential logic levels is different than the normal:
true: hi: 5v
lo:0v
false: hi: 0v
lo: 0v
Isolated ground is not the same as differential.
It seems you are looking for something completely isolated since there is no point in isolating the ground but not the signal line. Consider optical isolation or true differential which uses two wires but the logic is:
wire A = the input signal
wire B = the inverted input signal
You still have to keep both the differential wires within the allowed input voltage range of the differential receiver.
Brian.
You can't "separate the ground" without isolating the output driver or increasing the common mode impedance somehow.
Some additional information is necessary: type of cable, connection at the peer, single ended or differential receiver, uni- or bidirectional communication?
How about doing an impedance balanced line, this implies making the impedance to ground equal at the sending end, maybe 50 or 100 ohms in series with each leg, with one leg biased up a couple of volts to give a clear threshold?
You only drive one leg, and at the receiver you use something like a RS485 receiver chip to covert to singled ended referenced to the local ground, you must still meet the common mode range limits at the receiver obviously, and you get about 6dB less noise margin then you would with a differential drive setup, but it is still orders of magnitude better then an unbalanced line.
But seriously, if the link is slow use an opto, if fast use 8b10 or Manchester coding and a transformer....
Regards, Dan.
O.K., why not using a true differential driver, e.g. a RS422/485 driver IC?the cable is twisted pair
the receiver is differential
unidirectional
O.K., why not using a true differential driver, e.g. a RS422/485 driver IC?
Operating the connection in a pseudo differential manner (single-ended driver, differential receiver) gives some common mode rejection, too.
Yes, what's wrong with it if the receiver is differential?but the logic levels of those drivers are +-5v
Yes, what's wrong with it if the receiver is differential?
The levels are NOT +5V/-5V they are still 0V and +5V but the logic state of one wire relative to the other wire is opposite.I can't use either because I will need to use two separate supplies
I knowThe levels are NOT +5V/-5V they are still 0V and +5V but the logic state of one wire relative to the other wire is opposite.
To be honest, I can't see any point in using twisted pairs if the signal isn't differential. Twisting a single ended link actually makes the SNR worse!
Brian.
line length could be a few meters and the environment is noisy
Differential receiver? Opto coupler? Increasing confusion.
How about sketching the actual receiver circuit?
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