Lambda SR1, Operation Manual, Page: 182 / 317

SR1 Operation Manual 182
© 2014 Stanford Research Systems
Exponential, or continuous averaging, continuously updates the averaged FFT displays weighting recent
spectra more heavily than older spectra. The number of averages in this case is only an approximation of
how many spectra are included in the average. Linear averaging averages the specified number of
spectra, all equally weighted, and then stops. "None" means that no averaging is applied. In this case
the magnitude of the Linear Spectrum and Power Spectrum are the same. The "Clear" button clears the
current average buffer and restarts the averaging process. The "Average Done" indicator lights when the
required number of averages has been accumulated.
Other Jitter Analyzer Controls
Turning on "Time Domain Interpolation" applies band-limited interpolation to the time record of the Jitter
Analyzer. This is useful when looking at the time record display for jitter frequencies near the top of the
range where there are only a few samples per cycle. As an example, the plots below show time record
displays for a 100 mUI of 75 kHz sinusoidal jitter, with and without time domain interpolation.
75 kHz Sinusoidal Jitter Recorded w ithout Interpolation...
and w ith Tim e Dom ain Interpolation
Selecting one of the DC Correction options, either "Average" or "1/2 Pk-Pk" can reduce the DC offset in
the each jitter time-record and reduce the leakage from the DC bin in the spectra which can obscure low-
frequency details. Since jitter has intrinsically no DC component, the observed DC components are all
due to measurement artifacts.