Signal Margin
High speed serial transceiver compliance testing relies upon channel operating margin to quantify remaining signal amplitude relative to noise and intersymbol interference at a receiver decision point. Differential signaling traces etched onto printed circuit boards experience frequency dependent attenuation and crosstalk during high frequency data transmission. Automated test equipment measures equalization settings and pulse response parameters to calculate this ratio in decibels.
Signal degradation reduces eye height until jitter violations trigger bit error rate failures during final product verification.
Equalization Budget
Serdes transmitters and receivers apply continuous time linear equalization and decision feedback equalization to compensate for insertion loss profiles. Serial links operate successfully only when the combined equalization capability exceeds the channel operating margin penalty imposed by board material dissipation and via stub reflections. Laboratory engineers sweep voltage and timing parameters to verify that the remaining margin satisfies protocol specifications across manufacturing process variations.
Pre-layout simulation tools estimate trace geometries and dielectric constants to predict channel performance before purchasing expensive laminates.
Receiver Sensitivity
Differential inputs must detect low voltage swings reliably while rejecting high frequency common mode noise generated by neighbouring power planes and switching regulators. Circuit designers allocate specific proportions of the total voltage budget to receiver jitter tolerance and thermal noise floor limitations. Final assembly test fixtures apply calibrated sinusoidal interference to confirm that the recovered clock remains stable under worst case channel operating margin conditions.
Proper impedance matching minimizes reflections that would otherwise consume the available eye diagram opening and degrade link reliability.
