# Differential pairs or single ended signals for 1m cable

I have one control board and 3 additional boards for the power electronics, that send and receive data from the control board over a distance of ~1m (3ft). All signals are single ended.

I have to design the boards, but I'm not sure about the best connection method. I could use D-Sub cables, ribbon cable and so on. That's not the problem.

Each of the 3 additional boards receive following signals from the control board:

• 10x PWM @12kHz
• CLK @16Mhz
• 4x digital signal lines @low frequency (turn on the boards etc.)
• +15VDC @50mA
• -15VDC @50mA
• +5VDC @200mA
• Ground
• Analog Ground

And in the other direction, every power electronics board send following signals to the control board:

• 10x 1bit stream @16MHz
• 5x analog signals -10V to 10V @2mA

Now I'm unsure if I send them as single ended or use differential line drivers and receivers. What would you do?

That would be at least 34 lines as single ended with one ground and one analog ground connection. Where would you put the ground lines, between each signal? Then we're talking about ~70 lines per board. And could I use a differential pair cable or should it be straight ribbon cable? Or do know a better solution? 2 cables per board would be also okay, but not ideal.

If I use differential drivers and receivers for the PWM, CLK, analog and 1 bit stream signals, we're talking about 52 signal lines (26*2) + 4 slow digital lines + power and ground per board. 3 68 pin D-Sub cables with twisted pairs should work in this scenario or not? In my opinion this is the best alternative. But also the most expensive one, because I need 15 differential line drivers and 15 differential line receivers. 3 drivers and 12 receivers (each 4 channel) on the control board and on every power electronics board 3 receivers and 4 drivers, if I make every signal as differential pair. So is it necessary to use differential pairs? Maybe just for particular signals to reduce the number of ICs?

• Are all these boards in the same box? Jul 21, 2019 at 7:34
• @Jasen: No, the clock is for 10 sigma-delta modulators (AD7401A) that they have the same sample time. They send the 1bit stream to one FPGA for demodulation, which also sets the 16MHz clock. Jul 21, 2019 at 7:34
• @Mattman944 It's a prototype for the university. It's probably screwed to an aluminum frame or loose on the table. One board (300x320mm) is next to each other. Jul 21, 2019 at 7:39

At 16 MHZ ordinary ribbon cable should be fine, I'd look at using PATA (hard drive) cables, because they are available off the shelf cheaply.

I'd interleave the 16Mbaud data, with power and ground wires

 G d P d G d P d G


To reduce cross-talk and also separate the clock from that by a little bit

all the other signals as slow enough that they should not need any special treatment other than possibly low-pass filtering.

• Thanks a lot, do you think I could use a twisted pair cable? If so, how would you connect them? Because a 50 pin twisted pair D-Sub cable is very cheap and more rugged than a PATA cable and screwed in. But I couldn't find a cheap 50 pin D-Sub cable without twisted pairs. Jul 21, 2019 at 8:51
• twisted pair is usually for differential signalling, but it will work ok single-ended at 16Mhz Jul 21, 2019 at 19:31