What is the purpose of a differential pair?

What is the purpose of a differential pair?

In differential signaling, each signal is transmitted using a differential pair—the signal carried by one wire is the same level as the one carried by the other wire, but in opposite polarity. The signal at the receiving end is interpreted as the difference between the two lines that make up the differential pair.

What is the use of differential pair in PCB design?

Differential pair PCB routing is a design technique employed to create a balanced transmission system able to carry differential (equal and opposite) signals across a printed circuit board. Typically this differential routing will interface to an external differential transmission system, such as a connector and cable.

What are the rules for a differential pair?

These Rules are as follows: Rule 1 – The traces should be of equal length. This one of the most important rule that you should adhere to when implementing differential pairs. This ensures that there is no skew (timing differences) between the signals of the pair, and flight times will be identical.

How are differential pairs determined in PCB transmission lines?

It will also depend on current ‘I2’ in line 2 through coupling or mutual impedance ‘Zm’ between lines 1 and 2. This situation can be expressed by the following equation: Where ‘Zse’ is the characteristic impedance of line 1 and ‘Zm’ is the mutual or coupling impedance between line 1 and line 2.

How big is the gap between differential pairs?

Altium Designer has a good feature called Parallel Segment Rule, which maintains the gap between differential pair traces. The Rule of thumb is 2 x the trace width. So if you have 4 mil traces, then the gap should be 8 mil for a maximum length of 500 mils [2].

Which is the main signal in a differential pair?

Therefore, looking at equations (7a) and (7b) above, we need to emphasize that ‘Vcom’ (or ‘Veven’) is only a de bias voltage on the two lines of a differential pair. The main signal is the differential signal (‘V1 – V2’). Half of which is added to line 1, usually called the positive line.