Skew adjusted data cable
A twisted pair cable wherein characteristics of the twisted pairs, such as twist lay, insulation thickness, characteristic impedance, etc. are selected so as to achieve minimal skew between the twisted pairs. In some examples, insulation materials may be varied among the twisted pairs and composite insulations may be used for one or more pairs in a cable.
1. A cable having a specified characteristic impedance comprising:
a plurality of twisted pairs of insulated conductors designated into a first group of twisted pairs and a second group of twisted pairs;
wherein each twisted pair in the first group of twisted pairs has a first twist lay, a first insulation thickness and a first nominal impedance;
wherein each twisted pair in the second group of twisted pairs has a second twist lay, a second insulation thickness and a second nominal impedance; and
wherein a first combination of the first twist lay and the first insulation thickness, and a second combination of the second twist lay and the second insulation thickness are selected such that a difference between the first nominal impedance and the specified characteristic impedance of the cable is greater than about 2 Ohms and less than about 15 Ohms, and a difference between the second nominal impedance and the specified characteristic impedance of the cable is greater than about 2 Ohms and less than about 15 Ohms; and
wherein the cable has a skew of less than approximately 25 ns per 100 m.
2. The cable as claimed in claim 1 , wherein:
each twisted pair in the first group of twisted pairs has a first insulation material having a first dielectric constant;
each twisted pair in the second group of twisted pairs has a second insulation material having a second dielectric constant greater than the first dielectric constant;
wherein the second twist lay is greater than the first twist lay; and
wherein the second insulation material comprises a first layer material having a third dielectric constant and a second layer material, the second layer material being different from the first layer material and having a fourth dielectric constant such that the second dielectric constant is an effective dielectric constant of a combination the first and second layer materials.
3. The cable as claimed in claim 2 , wherein the first insulation material is fluoroethylenepropylene.
4. The cable as claimed in claim 2 , wherein the first layer material is a polyolefin.
5. The cable as claimed in claim 4 , wherein the first layer material is a polyolefin selected from the group consisting of polyethylene, flame retardant polyethylene, and polypropylene.
6. The cable as claimed in claim 4 , wherein the second layer material is a fluoropolymer.
7. The cable as claimed in claim 6 , wherein the second layer material is fluoroethylenepropylene.
8. The cable as claimed in claim 2 , wherein the second layer material is a fluoropolymer.
9. The cable as claimed in claim 8 , wherein the second layer material is fluoroethylenepropylene.
10. The cable as claimed in claim 1 , wherein the insulation of each twisted pair in the first group of twisted pairs is a composite formed of at least two different polyolefins.
11. The cable as claimed in claim 1 , wherein the first and second combinations are selected such that an impedance delta between the first nominal impedance and the second nominal impedance is in a range of about 8 Ohms to 15 Ohms.