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So, my question is this. I've got four differential pairs from an LVDS chip which need to go to a connector, along with a few single-ended signals.

For this purpose, I chose a hirose df13 connector.

I found out today, however, that there exist connectors specifically meant for differential pairs (e.g. Samtec QTH-DP)

Is that really necessary for differential pairs? In general, is there some necessary characteristic I need to look for in the connector I use when it comes to pairs?

On the flip side, if I were to use something like the QTH-DP, can I send single-ended signals through it? Or would I require 2 connectors, one for pairs and one for singles?

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  • \$\begingroup\$ Is it a board to board connector inside an enclosure, or will you use a cable to connect two enclosures? \$\endgroup\$ – bobflux Mar 18 '17 at 15:38
  • \$\begingroup\$ I'm not 100% sure what you mean by enclosure. They'll be inside the same device chassis. The connection will most likely be through a cable, rather than stacked boards, however. \$\endgroup\$ – user3765410 Mar 18 '17 at 16:31
  • \$\begingroup\$ It depends on the frequency and distance. High frequency / long distances require better connections. Sine your cables are in-box connections, distance probably is not an issue for you unless you are sending gigahertz signals. \$\endgroup\$ – Trevor_G Mar 18 '17 at 17:26
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I would use the Samtec QTH-DP and you can definitely send single ended signals through it. LVDS is defined as a 100 ohm differential signal, so this is a suitable connector.

You do not say just what speed (or more importantly, the edge rate) of your differential (or single ended) signals are, but if you use this type of connector you are covered at least for the LVDS pairs.

The typical single ended impedance is about 60 ohms through such a connector (this may well be in the report for the connector - Samtec is extremely good in providing such data).

I would note that Samtec offers complete cable assemblies for such board to board applications which can come in useful.

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If you cable length is more than 5 to 10% of a wavelength of highest spectral component in LVDS signal then you ought to use controlled impedance connectors that match your cable. This will reduce probability of errors with noise.

This applies only to single ended and differential controlled impedance signals. Slower rise time single signals may benefit from ground but may not need it. This Hirose connector is not suitable for differential LVDC pairs. (i.e. >155 Mbps)

Zo is controlled by the ratio of distributed inductance/gnd.capacitance ratio in the geometry of the connector.

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