Electronics > Projects, Designs, and Technical Stuff
About ribbon cables at fairly high frequencies.
Berni:
Ribbon cables can go really fast with the right pinout and plenty of grounds.
For single ended lines make the wires next to it ground. For differential put the pairs together and surround those with ground.
I ran plenty fast signals trough bog standard ribbon cable. Used it for MIPI display data at about 1Gbit over about 15cm. Had PCIe 2.0 (5 Gbit) running over about 10cm of it just fine. SATA III will also work just fine over it. Its all about having the right pinout. If you have a SPI bus with all the signals next to each other in the pinout then you can have problems even at 10 MHz, put the grounds in and its >100MHz no problem.
But as others have said once the cable gets long enough it should be treated like a transmission line. It needs to be driven by the correct impedance using series resistors and it needs something on the other end to terminate it. Do that and im pretty certain your I2S bus can run over 50m of ribbon cable and still work.
madires:
Old parallel SCSI supports up to 320MHz over ribbon cable.
Edit: 80 MHz DDR
helius:
--- Quote from: madires on July 23, 2020, 08:22:14 pm ---Old parallel SCSI supports up to 320MHz over ribbon cable.
--- End quote ---
No, SCSI-320 is 320 MB/s, for a 16-bit bus.
David Hess:
Tektronix had no problems using ribbon cables to transfer 100 MHz bandwidth signals inside oscilloscopes and under similar conditions, 100 MHz digital signals would work just as well. An example on the receiver side is shown below. The poor soldering is a quick repair job and unrelated to what needed to be diagnosed and repaired; thick gold plating makes for difficult soldering.
Update: When I say 100 MHz bandwidth, I should have included that that is with a minimum of aberrations in the 3.5 nanosecond step response.
schratterulrich:
a picture is worth a thousand words so I have made a quick and dirty measurement of a pcb with an attached ribbon cable.
TDR without cable:
TDR with cable:
I can see
1) launch from semirigid to pcb
2) section of pcb trace (coplanar waveguide on bottom) 74 Ohm
3) section of pcb trace (microstrip on top 0,15mm width FR-4 1,55mm)
4) thru hole with pin header, stub of pin, stub of ribbon cable,...
5) ribbon cable with quiet perfect 100 Ohm (G-S-G)
6) some capacitance at the end of ribbon cable
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