Differential signal layout

[EDA_hg81]

have to layout 9 pair Differential signal .

should all traces of Differential signal have the same length?

if those traces have the same length, the termation length should be included?

such as termation for RSDS signal as following **broken link removed**
Am I right?

Thanks

 

[House_Cat]

In general, it is not necessary for all differential pairs to be the same length. However, it is necessary for the positive and negative paths of an individual differential pair to be the same electrical length to prevent signal skew.

Whether or not to match all differential pairs to one another is determined by your application, and the clock rate. Some very high speed parallel data applications need to be matched between differential pairs because of signal timing limitations. In general, for most applications, small differences in signal transport time from one differential signal to the next caused by different signal path lengths is well within allowable signal timing margins. You need to determine for yourself if your circuit and data rate can tolerate different signal arrival times on the individual paths.

The terminator is the final destination for the signal; therefore, the two sides of a differential pair should be matched from source to terminator, and from source to the input of the next device or stage. The terminator is there to absorb the energy of the signal and minimize reflections on the line. If you tap the signal anywhere away from the terminator, you still need to be concerned about the flight time from the source to the final device or stage.

 

[nagaup3]

If there is a mismatch between the + signal and -signal of the differential pair it would increase the Common mode currents, there my increasing the crostalk. Hence reduce the mismatch to the possible extend. To do this sometimes the pins needs to be swapped and its good to plan at the begining of the project the pin mapping and routing possibilities rather then digging and modifing at the end.

Also if you have diff pair clocks used to trigger more than one circuits simultaneously then all diffpairs length should match.

The purpose of terminator is to provide a proper impedance matching for the signal propagation, thereby reducing reflections on the signal. Hence this should also be properly routed and length matched.

Good Luck!!!
Nagaraj.

 

[EDA_hg81]

Tahnk you all s much!

Have a good weekend.