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March, 2005 EEEL/ITL Offer Free Software for Oscilloscope Timebase Corrections |
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In a joint collaboration between EEEL and ITL, Paul Hale, Jack Wang, Dylan Williams, Kate Remley, and Joshua Wepman have demonstrated a new method of correcting both random and systematic timebase errors in sampling oscilloscopes. High-speed sampling oscilloscopes suffer from systematic timebase distortion (TBD) and random jitter that cause errors in the time in a waveform at which samples are acquired. The NIST researchers have constructed an alternative timebase, for use with conventional sampling oscilloscopes that greatly reduces both TBD and jitter. The new timebase relies upon the simultaneous measurement of the signal of interest and two reference sinusoids (in quadrature) that serve to determine the actual time at which the measurement was performed. The conventional timebase of the oscilloscope is used to characterize distortion in the two reference sinusoids and to determine within which half-cycle of the auxiliary sinusoids the signal was measured. The new timebase is estimated from the sinusoids using a weighted "total least squares" approach that accounts for relative contributions of additive noise and timing error. Sampling
oscilloscopes that have a form of jitter correction based on quadrature
sinusoidal reference signals have recently become commercially available.
The NIST correction method achieves the best aspects of these systems
simultaneously, including a residual jitter of less than 200 fs, a correction
of time records with nearly arbitrary length, and an application to signals
at almost any frequency. Furthermore, the NIST method is inexpensive,
since it can be implemented with an older generation of standard equipment.
It also corrects for both random jitter and systematic timebase distortion
and provides the user with an estimate of the residual timing error after
the correction process has been applied. Finally, the method is nonproprietary.
Details of the procedure are described in P.D. Hale, C.M. Wang, D.F. Williams,
K.A. Remley and J. Wepman, "Compensation of Random and Systematic
Timing Errors in Sampling Oscilloscopes," submitted for publication
in IEEE Trans. Microwave Theory and Tech. Both the preprint and software
package are available on the High-Speed
Measurements Project Web site. Contact:
Paul Hale, phone 303-497-5367 |