2.5Gbps jitter generator

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# 2.5Gbps jitter generator - PowerPoint PPT Presentation

2.5Gbps jitter generator. Part 1 final presentation. What is jitter?. By definition, jitter is the short term variation of the significant instants of a digital signal from their ideal positions in time. How does jittered signal look like?.

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### 2.5Gbps jitter generator

Part 1 final presentation

What is jitter?
• By definition, jitter is the short term variation of the significant instants of a digital signal from their ideal positions in time.
• Random jitter is generally assumed to follow a Gaussian distribution which is characterized by a mean ,
• and width .
• Deterministic jitter is limited, and is determined by its peak-to-peak value,
• .
Why jitter is important?
• The probability that the edge crosses
• the sampling point, causing a bit error, follows Gaussian distribution .
• The mean value is determined by the deterministic jitter component.
Jitter generation
• Random jitter is generated from the accumulation of random processes including thermal noise and shot noise.
• Deterministic jitter is the jitter generation from a variety of systematic effects.

The causes include duty-cycle distortion

(DCD), intersymbol interference (ISI), sinusoidal or periodic jitter (PJ) and crosstalk.

Jitter and BER budget :
• Assume we want to get BER of

This means

Jitter transfer and jitter tolerance
• Jitter transfer measures the clock recovery performance

of a network or network element as a function of jitter

frequency. It is measured by applying sinusoidal jitter of

specified amplitude and frequency,

to the data and measuring the output jitter amplitude at

that frequency, The jitter transfer is given by

Jitter tolerance

Jitter tolerance measures the ability of a device or system, primarily at the receiving end, to track large amounts of jitter without degrading the BER. It is the amplitude of sinusoidal jitter

applied to a device that results in an equivalent 1 dB reduction in sensitivity. The measurement is performed by first measuring the BER of the Device Under Test (DUT) without applied jitter. The signal power is attenuated until the onset of errors or until a specified BER, typically , is exceeded …

Jitter tolerance (continued)

The attenuation is reduced 1 dB and the signal is transmitted with applied sinusoidal jitter imposed on the clock. The jitter amplitude is increased until the onset of errors or the specified BER is exceeded. The resulting

jitter amplitude is the jitter tolerance at that frequency,

Jitter tolerance and transfer are primarily of interest in SONet/SDH/OTN applications.

Jitter Generator schematic:input structure
• AC coupling (RocketIO termination voltages are )
• End termination of differential line
• DC rebias
• Capacitive bypass filtering of reference

voltage VBB

Jitter Budget Calculation
• How much internal jitter do we generate?

NB4N11M DJ = 20ps

NB4N11MRJ (rms) = 1ps

SY100EP195 DJ = 25ps (DCD)

SY100EP195 RJ (rms) = 0.2ps

RocketIO TX DJ = 15 ps (DCD)

• Plus the jitter following from the ac-

coupling, as well as low-pass effects (ISI).

This amount will be estimated from Hyperlynx

simulation

How to apply jitter modulation frequency?
• Modulation frequency is controlled by the

rate of change of a digital control word to programmable delay chip.

Since the highest modulation frequency of