Reflection (electrical)
|
|
Reflection in electricity is the result of impedance mismatch in electrical signals. When voltage hits a discontinuity, some energy is reflected. This occurs in any change in a material’s final stop (Connection to another material).
Impedance discontinuities cause attenuation because a portion of a transmitted signal will be reflected back to the transmitting device rather than continuing to the receiver, much like an echo. This effect is compounded if there are multiple discontinuities causing additional portions of the remaining signal to be reflected back to the transmitter. This is a fundemental problem with the daisy chain method of connecting electronic components.
When this returning reflection strikes the first discontinuity, some of the signal rebounds in the direction of the original signal, creating multiple echo effects. The echoes strike the receiver at different intervals making it difficult for the receiver to accurately detect data values on the signal. This is called jitter and results in data errors.
The ratio of energy bounced back depends on the materials. Mathematically, it is calcuated using the reflection coefficient, symbolized with a gamma.
The combination of the effects of signal attenuation and impedance discontinuities on a communications link is called insertion loss. Proper network operation depends on constant characteristic impedance in all cables and connectors, with no impedance discontinuities in the entire cable system.