SNDR Measurements
Assuming ISI jitter and noise is 100% compensable by equalizers and is of no consequence to system performance, you can project a system's performance (when equalizers are used) by determining the ratio between the signal from linear fit pulse response and distortion-plus-noise. This ratio is called Signal to Noise and Distortion Ratio (SNDR). Some technology standard documents publish SNDR specifications.
The SNDR measurement is arrived at by performing linear fit pulse response and linear fit error (matrix) math functions on the input waveform and then by making calculations based on the results.
Signal to Noise and Distortion Ratio (SNDR) is defined by the equation:
Where:
- Pmax is a measure of the energy in p(k), which is the linear fit pulse response.
- σe is Sigma-e, the standard deviation of e(k), which is the linear fit error. The linear fit error is the difference between the input signal and the linear fit Pulse Corrected waveform; it represents essentially the distortion from a linear response.
- σn is Sigma-n, an averaged measurement of the RMS deviation from the mean voltage noise (σ) at all PAM levels. σn represents essentially the crosstalk and all other external noise.
The SNDR measurements include:
- :MEASure:SNDRatio:LMEans (Level Means)
- :MEASure:SNDRatio:PMAX (P-max)
- :MEASure:SNDRatio:RLMismatch (Ratio of Level Mismatch)
- :MEASure:SNDRatio:SERRor (Sigma-e)
- :MEASure:SNDRatio:SNDRatio (SNDR)
- :MEASure:SNDRatio:SNOise (Sigma-n)
- :MEASure:SNDRatio:SNPLevel (Sigma-n Per Level)
SNDR measurement parameters are defined for the waveform source selected.