Nicholas G. Paulter

An assessment on the accuracy of time-domain reflectometry for measuring the characteristic impedance of transmission lines

An assessment of time-domain reflectometry (TDR) for measuring the characteristic impedance Z/sub TL/ of transmission lines is performed. The assessment includes the accuracy of measuring ZTL as a function of TDR electrical impedance Z/sub o/, the ability to measure impedance perturbations as a function Of ZTL and Z/sub o/, and the ability to differentiate between transmission lines of similar ZTL. The information presented will be especially useful for those using 50 /spl Omega/ TDR systems to characterize transmission lines having characteristic impedances less than about 30 /spl Omega/.

A fast pulse oscilloscope calibration system

A system is described for calibrating high-bandwidth oscilloscopes using pulse signals. The fast-pulse oscilloscope calibration system (FPOCS) is to be used to determine the step response parameters for digitizing oscilloscopes having bandwidths of /spl sim/20 GHz. The system can provide measurement traceability to standards maintained at the U.S. National Institute of Standards and Technology (NIST). It comprises fast electrical step generation hardware, a personal computer (PC) and software, and a reference waveform, i.e., a data file containing an estimate of the step generator output signal. The reference waveform is produced by prior measurement by NIST of the step generator output signal (calibration step signal). When the FPOCS is in use, the calibration step signal is applied to the device under test, which is an oscilloscope sampling channel. The measured step waveform is corrected for timebase errors, then the reference waveform is deconvolved from it. The results are impulse, step, and frequency response estimates, and their associated parameters (e.g., transition duration, transition amplitude, -3 dB bandwidth) and uncertainties. The system and its components are described, and preliminary test results are presented.

Long-term repeatability of a TDR-based printed wiring board dielectric constant measurement system

A new time-domain-reflectometry-based method has been recently developed that provides accurate determinations of the dielectric constant of printed wiring board dielectrics over the frequency range of 0.1 GHz to 10 GHz. The long-term measurement reproducibility, as well as the short-term measurement repeatability, of that method were investigated and the results are reported here.

Pulse parameter uncertainty analysis

A detailed uncertainty analysis is presented for the pulse parameter measurement service of the National Institute of Standards and Technology (NIST, USA). It relates to the new pulse parameter measurement and extraction processes. Uncertainties for pulse amplitude, transition duration, overshoot and undershoot (preshoot) are given. Effects of temperature variation, impulse response estimate, pulse parameter extraction algorithms, time-base distortion, calibration procedures and the waveform reconstruction process are included.

NIST-NPL interlaboratory pulse measurement comparison

A comparison of the pulse parameter values obtained from the pulse measurement services of the National Institute of Standards and Technology, USA, and the National Physical Laboratory, U.K., was performed. The comparison was based on the pulse parameters of amplitude, transition duration, overshoot, and undershoot (preshoot). The parameter comparison was applied to raw (measured) waveforms, corrected waveforms (if applicable), and reconstructed waveforms. The results of the comparison show that the pulse parameter values for both national laboratories are within published uncertainties.

A causal regularizing deconvolution filter for optimal waveform reconstruction

A causal regularizing filter is described for selecting an optimal reconstruction of a signal from a deconvolution of its measured data and the measurement instruments impulse response. Measurement noise and uncertainties in the instruments response can cause the deconvolution (or inverse problem) to be ill-posed, thereby precluding accurate signal restoration. Nevertheless, close approximations to the signal may be obtained by using reconstruction techniques that alter the problem so that it becomes numerically solvable. A regularizing reconstruction technique is implemented that automatically selects the optimal reconstruction via an adjustable parameter and a specific stopping criterion, which is also described. Waveforms reconstructed using this filter do not exhibit large oscillations near transients as observed in other regularized reconstructions. Furthermore, convergence to the optimal solution is rapid. >

Sources of uncertainty in the nose-to-nose sampler calibration method

We analyze the nose-to-nose (ntn) method for use as an accurate sampler calibration method. The variations in the measurement of the sampler impulse response using the ntn method are presented, and the validity of the assertion that the kick-out pulse is identical to the sampler impulse response is assessed. Temperature effects on the ntn method are also examined. Finally, the impact of uncertainties in the ntn calibration method on the uncertainties in reported pulse parameters is examined.

Reducing the effects of record truncation discontinuities in waveform reconstructions

Record truncation discontinuities (RTDs) are artifacts in recorded data caused by the difference between the values of the data at the two ends of the record. The RTD causes errors in waveform reconstructions, in particular, in digital reconstructions that use a deconvolution process. The effects of the RTDs on reconstructions of discrete-time waveforms are examined. Four previously proposed methods for reducing the effects of RTD on the spectra of step-like waveforms are examined for application in deconvolution, and a comparison of their effects in deconvolution is given. An analysis of the errors is given for each case. >

Low-jitter trigger system for pulse calibration and intercomparison of high-speed samplers

A low-jitter (<1 ps) trigger system for pulse-waveform-based calibration and intercomparison of high-speed samplers is described. The system uses a commercially available pulse generator and pulse splitter/delay line.

The “Median” Method for the Reduction of Noise and Trigger Jitter on Waveform Data

The “median” method for the reduction of the effect of noise and trigger jitter on waveform data is described. The effectiveness of this method was examined using simulations and experiments and, for typical jitter and noise observed in electrical pulse metrology, is shown to provide reconstructed waveforms with transition durations that accurately match those of the input signal. Also, for aberrations, an upper bound on the error in the amplitude of the aberration is provided.