眼图skew求助
时间：10-02
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请问一下大家，在仿真的时候眼图的skew是指的那部分，那种情况为skew,求详细解释，最好能配图说明，小弟不胜感激
Eye Height
The eye height is a measure of the signal-to-noise ratio of a signal. The mean of the “0” level is subtracted from the mean of the “1” level as in the eye amplitude measurement. This number is modified by subtracting the standard deviation of both the “1” and “0” levels. The measurement basically gives an indication of the eye opening.
Eye Width
This measurement gives an indication of the total jitter in the signal. The time between the crossing points is computed by measuring the mean of the histograms at the two zero crossings in the signal. The standard deviation of each distribution is subtracted from the difference between these two means.
Extinction Ratio
This measurement, defined only for optical signals, is the ratio of the optical power when the laser is in the ON state to that of the laser in the OFF state. Laser transmitters are never fully shut off because a relatively long period of time is required to turn the laser back on, thus limiting the rate at which the laser can operate. The extinction ratio is the ratio of two power levels (one very near zero) and its accuracy is greatly affected by any offset in the input of the measurement system. Optical signals are measured using optical-to-electrical converters on the front end of the SDA. Any DC offset in the O/E must be removed prior to measurement of the extinction ratio. This procedure is known as dark calibration. The output of the O/E is measured with no signal attached (i.e., dark), and this value is subtracted from all subsequent measurements.
Eye Crossing
Eye crossing is the point at which the transitions from 0 to 1 and from 1 to 0 reach the same amplitude. This is the point on the eye diagram where the rising and falling edges intersect. The eye crossing is expressed as a percentage of the total eye amplitude. The eye crossing level is measured by finding the minimum histogram width of a slice taken across the eye diagram in the horizontal direction as the vertical displacement of this slice is varied.
Average Power
The average power is a measure of the mean vale of all levels that the data stream contains. It can be viewed as the mean of a histogram of a vertical slice through the waveform covering an entire bit interval. Unlike the eye amplitude measurement where we separate the ones and zeroes histograms, the average power is the mean of both histograms. Depending on the data coding that is used, the average power can be affected by the data pattern. A higher density of ones, for example, will result in a higher average power. Most coding schemes are designed to maintain an even ones density resulting in an average power that is 50% of the overall eye amplitude.
Q Factor or BER
The Q factor is a measure of the overall signal-to-noise ratio of the data signal. It is computed by taking the eye amplitude (the difference between the mean values of the "1" and "0" levels) and dividing it by the sum of the noise values (standard deviations of the "1" and "0" levels). All of these measurements are taken in the center (usually 20%) of the eye.
eyeBER
EyeBER is the estimated bit error rate from an eye diagram. It is calculated using the intersection of the distribution of the one and zero levels. EyeBER differs from BER in that eyeBER is calculated from Q-factor and is, therefore, based on signal-to-noise ratio; BER, on the other hand, is based on jitter.
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眼图参数测量
Eye Pattern Measurements
There are several important measurements that are made on eye patterns. These are specified as required tests for many standards. Eye measurements mainly deal with amplitude and timing, which are outlined below.
Eye Amplitude
Eye amplitude is a measure of the amplitude of the data signal. The measurement is made using the distribution of amplitude values in a region near the center of the eye (normally 20% of the distance between the zero crossing times). The simple mean of the distribution around the “0” level is subtracted from the mean of the distribution around the “1” level. This difference is expressed in units of the signal amplitude (normally voltage).
Eye Height
The eye height is a measure of the signal-to-noise ratio of a signal. The mean of the “0” level is subtracted from the mean of the “1” level as in the eye amplitude measurement. This number is modified by subtracting the standard deviation of both the “1” and “0” levels. The measurement basically gives an indication of the eye opening.
Eye Width
This measurement gives an indication of the total jitter in the signal. The time between the crossing points is computed by measuring the mean of the histograms at the two zero crossings in the signal. The standard deviation of each distribution is subtracted from the difference between these two means.
Extinction Ratio
This measurement, defined only for optical signals, is the ratio of the optical power when the laser is in the ON state to that of the laser in the OFF state. Laser transmitters are never fully shut off because a relatively long period of time is required to turn the laser back on, thus limiting the rate at which the laser can operate. The extinction ratio is the ratio of two power levels (one very near zero) and its accuracy is greatly affected by any offset in the input of the measurement system. Optical signals are measured using optical-to-electrical converters on the front end of the SDA. Any DC offset in the O/E must be removed prior to measurement of the extinction ratio. This procedure is known as dark calibration. The output of the O/E is measured with no signal attached (i.e., dark), and this value is subtracted from all subsequent measurements.
Eye Crossing
Eye crossing is the point at which the transitions from 0 to 1 and from 1 to 0 reach the same amplitude. This is the point on the eye diagram where the rising and falling edges intersect. The eye crossing is expressed as a percentage of the total eye amplitude. The eye crossing level is measured by finding the minimum histogram width of a slice taken across the eye diagram in the horizontal direction as the vertical displacement of this slice is varied.
Average Power
The average power is a measure of the mean vale of all levels that the data stream contains. It can be viewed as the mean of a histogram of a vertical slice through the waveform covering an entire bit interval. Unlike the eye amplitude measurement where we separate the ones and zeroes histograms, the average power is the mean of both histograms. Depending on the data coding that is used, the average power can be affected by the data pattern. A higher density of ones, for example, will result in a higher average power. Most coding schemes are designed to maintain an even ones density resulting in an average power that is 50% of the overall eye amplitude.
Q Factor or BER
The Q factor is a measure of the overall signal-to-noise ratio of the data signal. It is computed by taking the eye amplitude (the difference between the mean values of the "1" and "0" levels) and dividing it by the sum of the noise values (standard deviations of the "1" and "0" levels). All of these measurements are taken in the center (usually 20%) of the eye.
eyeBER
EyeBER is the estimated bit error rate from an eye diagram. It is calculated using the intersection of the distribution of the one and zero levels. EyeBER differs from BER in that eyeBER is calculated from Q-factor and is, therefore, based on signal-to-noise ratio; BER, on the other hand, is based on jitter.
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非常用心的分享！谢谢 goodbye网友
非常用心的分享！谢谢 goodbye网友
什么意思
?
文章很好
对于DQ，是指所有DQ的在Vref处的最大偏差时间，DQS是在crosspoint的最大偏差时间则是jitter