User`s guide

Error Tolerance (UI) - Measurements of an edge that exceed this value will cause an error.
Extended (Calibration) - The "Extended" check box will allow the user to select increased time periods for the Timer
Calibration. Extended (internal) Calibration allows the user to possibly reduce jitter due to the noise floor of the
instrument through the use of longer internal calibration periods. A pull down menu to the right of the Extended
check box selects the length of the calibration. Note: performing a short length calibration immediately after a
longer one will result in the loss of the earlier calibration information because the entire contents of the internal
tables are replaced with each calibration.
External Arming - Selecting External Arm allows an external signal source to arm the instrument using any input. Once
armed, the instrument measures the next pulse presented, with one measurement collected each time the External Arm
signal is received.
The number of measurements corresponds to the sample size selected. When the number of measurements equal to the
sample size is collected, computations are made and displayed in the statistics menus. The required Arm signal is any
pulse with a minimum duration of 1ns pulse width occurring 3ns before the signal on the input. See also Auto Arming.
External Calibration - Performs a calibration of the OE-2. Step by step instructions are displayed.
Eye Mask Options button - This button opens a menu for configuring an eye mask.
Fall Time Limit - Pass-Fail limit for fall time measurement. This is set automatically if a protocol has been chosen.
FFT 1-clk - Will measure maximum amount of jitter between two adjacent clock cycles. The low frequency end of this
view is rolled off at 20dB/decade showing the jitter frequency effects on a single clock period. This method is
insensitive to low frequency jitter.
Used to identify a frequency component’s contribution to period jitter. This is critical in applications with sensitivities
to period deviation. Here, the user is interested in seeing what is causing period jitter. Applications sensitive to this
include microprocessors, digital logic, DSP chips and other synchronous architectures. These users are also usually
interested in cycle-cycle jitter, period jitter and other signal metrics as they relate to high frequency timing deviations.
FFT Alpha Factor - The varying of the Alpha Factor illustrates the inverse proportionality relationship between the
spectral peak width and the sidelobe rejection of the Kaiser-Bessel window. As the Alpha Factor increases, the
spectral peak widens and the sidelobes shrink. As the Alpha Factor decreases, the spectral peak narrows and the
sidelobes increase in amplitude.
FFT in dBs command (Display menu) - If checked, FFT’s will be displayed in decibels.
FFT N-clk - Will measure maximum amount of jitter between any two-clock cycles. This method is sensitive to low
frequency jitter. All jitter frequencies have an equal effect on the clock in this view.
Used to compare frequency content of the timing noise relative to an ideal clock. This essentially measures a frequency
component's contribution to overall time base deviation relative to an ideal (non-jittered) clock. This type of measurement
is typical of applications sensitive to cumulative jitter such as communications devices and audio digitization.
When looking at jitter in specific frequency bands, it is critical to use the "n-clock" FFT since the amplitudes within the
band must be compared to an ideal clock.
FFT, Padding Multiplier - Padding increases the frequency resolution of the FFT. Generally, a higher padding value
will increase transformation processing time.
FFT Window - To reduce spectral information distortion of FFT’s, the time domain signal is multiplied by a window
weighting function before the transform is performed. The choice of window will determine which spectral components
will be isolated, or separated, from the dominant frequency(s). Each window function has advantages/disadvantages
over other windows.
FFT, Blackman - Broad central peak. Good sidelobe rejection.
FFT, Gaussian - Very broad central peak. No sidelobes.
FFT, Hamming - Moderately sharp central peak. Poor sidelobes. First sidelobe cancellation.
FFT, Hanning - Reasonable sidelobe rejection. Central peak as narrow as triangular window. Faster sidelobe
fall-off than triangular window.
FFT, Kaiser-Bessel - Very narrow spectral peak. Very large sidelobes. The Kaiser-Bessel FFT is the only FFT
that has the Alpha Factor feature that contributes to the versatility of this FFT.
FFT, Rectangular - No window weighting.
FFT, Triangular - Narrow spectral peak. Large sidelobes. Moderate fall-off.
Glossary © WAVECREST Corporation 2005
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