Question

13. Consider the enclosed eye diagram a. Explain what eye diagram is and what it is used for. b. Estimate the power penalty from the enclosed eye diagram. c. Explain the difference between power penalty and receiver sensitivity referring to the phenomena causing each of these specifications?

Answer 1

Ans a:

An eye diagram is used in digital communication to visualize the signal quality in the digital form. The effects of noise and distortion can be seen with the eye diagram. This technique mainly provides qualitative analysis. The trends can be identified. As shown in the enclosed eye diagrams the original signal and the received signal. Noise can be observed for both signal 1 and signal 0. The amplitude differences at the zero crossing represent the timing jitter. It creates uncertainty in the sampling position can lead to error. Jitter generally decrease the Signal to Noise ratio.

the figure shows the original signal is shown

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The following figure shows the received signal with noise represented by eye diagram,

V_D1 represents the noise in the amplitude of the signal1 and V_D0 is the noise in the amplitude of the signal 0.

Ans b:

Power penalty is the increase in the received power in order to keep bit error rate constant i.e. equal to bit error rate without jitter factor. A level of distortion and intersymbol interference results in reduced received signal level for signal1 and increased received signal level for 0 signal. The measured power penalty from the eye diagram is given.

Power penalty = 10log₁₀ [(V_D1-V_D0)/ (V₁-V₀)] dB.

Ans c:

Receiver sensitivity is defined as the minimum received optical power required to achieve the targeted bit error rate (BER). Performance of the receiver can be measured with a low bit error rate. The difference between the power penalty and receiver sensitivity is clear. Receiver sensitivity is the minimum average optical power received to achieve targeted BER while power penalty is the extra increase in the received power to ensure a constant BER.

As shown in the figure

下me Pes

IF V>V_ref then received signal is 1.

IF V<V_ref then received signal is 0.