# Reconstruction of differential signal

I have a differential signal which will be transmitted from a system (transmits and receives the data through 2 wires only, there is no GND wire).The differential signal has 3 voltage levels -12V , 0V and +12V. I have measured this differential signal with the help of oscilloscope by keeping one wire to GND of oscilloscope and one wire to positive of Oscilloscope. The differential signal was shown below.

I need to decode this data i.e, convert to single ended signal but here the issue is when this differential is converted to single ended signal using AM26LS31CDBR IC, 0V logic level is either converted to High or low, but it is not following the same logic i.e. High or low. I need a transceiver which converts this three state differential signal to single ended signal and it also should convert the same converted single ended signal to differential which should be same as three state differential input signal .

Can anyone suggest me the solution for reconstructing the differential signal.

• Don't use a differential logic receiver, use a differential amplifier. This is one of the basic uses of operational amplifiers. You may want to consult wikipedia for this.
– sh-
Jan 5, 2021 at 13:05
• As clear as mud. Jan 5, 2021 at 14:17

To receive a differential signal, one would use a differential amplifier like this:

simulate this circuit – Schematic created using CircuitLab

The operational amplifier must be selected to have the necessary speed, depending on the signal to be received. With the given resistor values, the gain is 1, so a differential input of 12V will generate a single ended output of 12V. This can be changed, if needed.

• "I need a transceiver which converts this three state differential signal to single ended signal and it also should convert the same converted single ended signal to differential which should be same as three state differential input signal" He wants to reconstruct, as he said it, from single ended output back to differential output. How does your circuit do that. It just gives output that is difference of inputs. Jan 5, 2021 at 17:41
• The differential amplifier above does the first part of the job: It converts the differential -12V/0V/12V signal to a single ended signal with the same voltages with respect to ground. Converting this back to a differential signal with those voltages can be done with balanced drivers such as the THAT1420 or the DRV134 (beware: they have gain).
– sh-
Jan 6, 2021 at 19:51
• Or use two op amps like i suggested. Total cost 2$. DRV134 on mouser costs 4.5$ ( I just checked the price, not what it is or what it does and i don't care what it does ). Also, I think that OP doesn't know what differencial signal is. Your circuit does not do what he asked, mine does and at lower cost. This is simple signal contitioning problem, no need for differencial amplifier since it is not differencial signal ( Look at the image he included, it's a square wave not differencial singal ). Jan 7, 2021 at 12:22
• Also, I wont respond to this thread no more since OP doesn't seem to be interested in this at all (Lack of interaction). I would recomend it to you as well to not waste your time on this no more Jan 7, 2021 at 12:35

If I understand correctly, you have 3 voltages, -12V , 0V, +12V. You then wish to translate it to 0V , xV, +12V and then those voltages back to -12V , 0V, +12V. If so, you can bring your input to op amp that is connected as inverting amplifier which has an offset voltage on its non inverting input. That way you can get voltages between 0V and +12V. Then do the same step to get -12V , 0V, +12V. (Output from op amp to second op amp)

This is the circuit (UPDATED)

Red [Vi] - original signal

Blue [Vo1] - 0V - +12V

Green [Vo2] - -12V - +12V --> Reconstructed

• The OP wrote that his input is differential. So instead of the inverting amplifier you drew, I'd go for a differential amplifier.
– sh-
Jan 5, 2021 at 15:00
• If I understood correctly, this circuit gets the job done. I've added a graph of simulation I've done. If you would have done it differently, show it with differential amplifier. Jan 5, 2021 at 16:14