Page 246 - Optical Communications Essentials

Performance Measures

236 Chapter Fourteen

Overshoot on logic 1
80-to-20%
20-to-80% Fall time
Rise time

b on
80%

Eye jitter Eye jitter

Eye-opening
height Zero crossing

20%
b off
b dark
Eye width Overshoot on logic 0
Undershoot on logic 0
Figure 14.2. General configuration of an eye diagram showing definitions of fun-
damental measurement parameters.

Figure 14.3. Simplified eye diagram showing key performance parameters.
■ The height of the eye opening at the specified sampling time shows the noise
margin or immunity to noise. Noise margin is the percentage ratio of the peak
signal voltage V 1 for an alternating bit sequence (defined by the height of the
eye opening) to the maximum signal voltage V 2 as measured from the thresh-
old level, as shown in Fig. 14.3. That is,

V 1
Noise margin (percent) 100 percent (14.3)
V 2

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