LeCroy DDA 7 Zi series, Руководство оператора

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WavePro 7Zi
403
WP700Zi-OM-E-RevA
Jitter Measurements
Tj Total jitter at a specific BER. The value is determined by the width of the curve expressing
the confidence limits of the extrapolated TIE histogram. The value represents the expected
range of values observed for a number of observed measurements equal to 1/BER. The Tj
parameter is accumulated over all acquisitions since the start of the measurement or the last
clear sweeps operation. The total population of the TIE histogram is indicated in the waveform
descriptor box for the bathtub curve and Htie (the TIE histogram).
Rj Random jitter is obtained indirectly by first determining deterministic jitter through various
direct analyses of the TIE trend. Once all of Dj is found, the Rj value is deduced from the
equation Rj = (Tj(BER) - Dj)/ Tj
(1-sigma)
(BER), where the value for BER is typically 10e-12 (i.e.,
Rj is not a function, but a single value). The bit error rate is selected in the @BER (pow 10)
control in the jitter menu. Rj is expressed in terms of an rms value, whereas Tj and Dj are
expressed as peak-to-peak values.
Dj Deterministic jitter is the peak-to-peak non-random part of the total jitter. This parameter is
the sum of the measured peak-to-peak values of periodic jitter (Pj) and data dependent jitter
(DDj). The DDj includes the effects of both inter symbol interference and duty cycle distortion.
Pj Peak-to-peak magnitude of the periodic components of the TIE trend. It is measured by
analyzing peaks in the Fourier transform of the trend of the time interval error. It is necessary to
specify the pattern repetition length (if there is one) so that spectral lines harmonically related
to this pattern rate do not contribute to the estimate of Pj, since the spectral energy associated
with data pattern-related spectral components is included in the DDj measurement. The total
periodic jitter is the complex sum of the spectral components listed in the table under the Pj
breakdown tab.
DCD Duty Cycle Distortion is the mean difference between the width of positive going pulses
(low to high to low) and negative going pulses (high to low to high) measured over all pulses in
the acquired waveform. The widths are measured at the same amplitude as specified for TIE
(i.e., not necessarily at 50% of the signal amplitude). This measurement is a component of DDJ
and included in the DDj value.
DDj The peak-to-peak jitter caused by systematic effects related to the sequence of data
transitions.
Pj Breakdown
The Pj Breakdown tab reveals a table of components of periodic jitter. This table lists the peak-to-peak amplitude
and rate (frequency) of each Pj component. The components are listed from largest to smallest. The Pj readout
below the grid on the display is the complex sum of the components listed in this table.
Alternate Jitter Breakdown Methods
There are two additional jitter breakdown methods. These methods are termed Effective and MJSQ and are
selected in the Jitter Calc. Method control. The Effective and MJSQ methods provide alternate ways of
determining the random and deterministic jitter but do not include the breakdown of deterministic jitter into
periodic and data dependent parts. When either of these modes is selected, the jitter breakdown button the jitter
menu becomes grayed (unavailable) and only the basic jitter display is shown. The DDj plot can still be viewed in
this mode; however, the information from this plot is not used in the computation of Dj.
Effective Jitter
The effective jitter mode is entered when Effective is selected in the Jitter Calc Method control. Effective jitter is
determined from the measured total jitter by evaluating the total jitter at several bit error rate values and solving Tj
= Tj
(sigma=1)
(BER)*Rje + Dje. The term Tj
(sigma=1)
is the total jitter of a Gaussian (normal) distribution of jitter with a
standard deviation of 1 second. The two unknowns in this equation (Rje and Dje) are found by solving for several