Twisted pair cable impedance, Delay, Inductance, Capacitance Calculator

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Enter the cable core diameter, distance between the core and the dielectric, then press the calculate button to get the twisted pair cable impedance, delay, inductance and capacitance.

Diameter of Wire:  
Seperation Between Wires:  
Substrate Dielectric:  
   
Impedance Ohms
Delay ns/in
Inductance per inch nH/in
Capacitance per inch pF/in

Twisted pair cable impedance, Delay, Inductance, Capacitance calculation:

Twisted pair cable is used to transmit the signal, here one cable will be data and another one will be ground. Twisted pair cable impedance Zo(twisted) in Ohms is equal to 120 times of natural logarithmic of ratio of 2 times of distance between the wires in meter to diameter in mm of the core and divided by root of the substrate dielectric.

Substrate dielectric is a constant and it depending on the type of material. For Standard FR4 substrates have the dielectric of approx. 4.5 and the ceramic-filled PTFE substrates have 3 to 10.

Hence we can write the formula such as,

Zo(twisted) = 120 x ln [2s/d] / √(er)

Signal delay in ns/in is equal to 0.08472 times of the root of substrate dielectric constant.

Delay (twisted) = 0.08472 x √(er)

Like that, the cable inductance nH/in (Nano Hendry per inch) is equal to the 0.00000001016 times of the natural logarithmic of ratio between two times of distance between the cores to diameter of the core.

L(twisted) = 0.00000001016 x ln [2s/d]

The capacitance of the twisted pair cable in pF/in will be 0.7065 times of substrate dielectric constant divided by the natural logarithmic of ratio between two times of distance in meter between the cores to diameter of the core in meter.

C(twisted) = 0.7065 x er ­/ ln [2s/d]

Example:

Let us calculate the ceramic-filled PTFE (er =  4) twisted pair cable impedance, delay, inductance and the capacitance for the 2 mm diameter cable and the distance between the two cores will be 4mm.

Here

d= 2 mm,

s = 4mm,

er = 4,

Hence the twisted pair cable impedance will be,

Zo(twisted)  = 120 x ln (2 x 0.004 / 0.002) / √(4)

= 83.2 ohms

Delay = 0.08472  x 2 = 0.169 ns/in

Inductance = 14.1 nH/in

Capacitance per inch =    2.04 pF/in

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