In a normal coaxial cable there are two fundamental components of cable loss: skin-impact loss and dielectric loss.
At high frequencies, the signal has a tendency to propagate alongside the floor of the inner conductor. This is referred to as skin-impact loss. This pores and skin depth (δ) is defined as:
where ω is the frequency in rad/s, µ is the conductor’s magnetic permeability in h/m, and ρ is the conductor’s resistance in ohmmeters. The pores and skin-impact loss causes the resistance per unit period and the inductance in step with unit period. The resistance according to unit duration is calculated as:
where w is the width of the conductor. For a round cord of radius r, the width is 2πr. The go back direction resistance also wishes to be added, but it’s far generally a good deal much less than the forward route and may be overlooked.
The dielectric insulator, additionally contributes to frequency-structured cable losses. The dielectric consistent (ε) is described as:
In which ε’ is the actual element of the dielectric regular, and tanδ represents the imaginary, or loss tangent, dissipation component of the dielectric. Due to the fact the dielectric insulator influences capacitance, the capacitance in keeping with unit length (cl) changes to cl (1 + jtanδ).
We reap the subsequent important points about cable losses:
- All cables have losses, and these losses will ultimately limit the performance of a gadget. The quantity of the loss relies upon at the first-rate of the cable and its specifications.
- The losses that do arise are:
- skin-impact losses, which dominate at low frequencies
- dielectric losses, which dominate at high frequencies
- go back-course losses, which might be insignificant and can be unnoticed for maximum instances
- losses through connectors, relays, and different connections made to the output nodes or the DUT
Performance degradations due to cable loss
For testers that run within the 200mbps range, cable loss won’t be a huge situation. However, for testers walking at 500mbps and better, the performance of the full signal course, electronics, cable, and pin ought to be analysed very carefully to ensure that full performance is measured effectively at the pin. The subsequent performance specs are the maximum vital for a high-velocity tester:
- dc accuracy of the waveform degrees
- rise and fall times
- maximum toggle fee
- minimal pulse-width capability
- propagation accuracy and matching relative to every facet
- propagation skews, which includes propagation vs. minimal pulse width, amplitude, and common mode