Twinax cables are specifically designed for improved performance in high-speed data applications. Compared to coaxial cable, which has a single conductor, twinax cable improves signal integrity, speed, and bandwidth by incorporating two conductors in its design.
The main benefit of twinax over micro coax is its ability to transmit a high-speed differential pair with very low intrapair skew between the positive and negative signal of that differential pair. Skew is the time delay difference between the positive and negative signals of the differential pair. Intrapair skew refers to the skew within the pair itself, rather than between two differential pairs. With the sophistication of the silicon today — the chips, FPGAs— the skew difference from pair to pair is becoming less and less of a concern, but that intrapair skew, the skew within the differential pair itself or within a single twinax, is still extremely critical. It’s becoming even more critical as data rates get to 112 Gb/s PAM4 and looking at 224 Gb/s PAM4.
Twinax cable construction
Primarily four components make up a twinax:
- The inner conductors or signal conductors carry the signal. Twinax has one positive and one negative signal conductor.
- The dielectric is the non-conductive material around the signal conductors.
- The shield, used for ground return, wraps around the two conductors in the dielectric.
- The jacket, or outer insulation, covers the shield.
The structure of a twinax cable is what allows for that decrease in intrapair skew and the resulting improvement in signal integrity. In most twinax cables, each signal conductor is extruded into a dielectric (made of a plastic polymer or other non-conductive material). The two conductors wrapped in a shield creates that twinax structure.
