Meaning
The reduction in the ratio of incident power to reflected power in a transmission line indicates a loss of signal integrity in high-frequency circuits. This electrical degradation, termed return loss degradation, occurs when impedance discontinuities along the signal path cause more energy to be reflected back toward the source. It is monitored to ensure that transmission lines meet performance specifications.
Signal Reflection
Impedance matching is required to ensure that the maximum amount of signal power is transmitted from the source to the load. When a signal encounters a change in impedance, a portion of the wave is reflected, which reduces the return loss. This can be caused by routing errors, vias, or defects in the circuit board laminate.
Impedance Discontinuity
Severe reductions in return loss can cause multiple reflections to travel back and forth along the transmission line, creating noise that distorts the received signal. This distortion degrades the eye diagram, leading to increased jitter and higher bit error rates in digital systems. In RF systems, it reduces the overall efficiency of the transmitter and can damage sensitive components.
System Integrity
Designers use time-domain reflectometry to locate the sources of reflections and optimize the trace geometry to restore return loss to acceptable levels. This process is essential for maintaining signal path quality.
