Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Analysis of complex waves
Reexamination Certificate
1998-06-13
2001-06-05
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Analysis of complex waves
Reexamination Certificate
active
06242899
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
This invention relates to test and measurement equipment. Specifically the invention is directed toward a waveform translator, i.e., translating the frequency spectrum of a repetitive non band limited input signal, to an equivalent frequency spectrum which is harmonically related to a fixed reference frequency. An analog to digital converter is clocked at the reference frequency to produce a digitized waveform with a predetermined integer number of data points per cycle corresponding to the input signal.
BACKGROUND—DESCRIPTION OF PRIOR ART
There was a long felt and unsolved need to display time domain waveforms from DC through the millimeter wave range. Although some attempts have been made in this direction with sampling oscilloscopes, none have been successful. The reason for this is that recent attempts have tried to leverage off existing technology, and new technology is required for the vertical sampler section and the horizontal timing section.
In a sequential sampling oscilloscope the input waveform is sampled at a selected point which is moved incrementally along the input waveform at each successive recurrence of the input waveform. The horizontal sweep circuits should provide the horizontal displacement of successive samples along the displayed waveform as a function of time.
U.S. Pat. No. 3,010,071 issued Nov. 21, 1961 to A. R. Carlson relates to sweep circuits in sequential sampling oscilloscopes. An input trigger circuit is required which is capable of precisely detecting a predetermined trigger level on the input waveform and which initiates the start of a fast ramp voltage generator. A voltage comparator circuit is provided which is capable of precisely detecting coincidence between a generated staircase voltage and the fast ramp voltage and which provides a sampling trigger pulse at the precise instant of coincidence. The circuit increments the staircase voltage on each recurrence of the input waveform. The time resolution and accuracy of this technique is extremely limited by the speed and linearity of the fast ramp voltage circuit, the dynamic accuracy of the voltage comparator and the accuracy of the staircase voltage generator. In addition, this technique is further limited by the necessity to trigger the fast ramp voltage generator in synchronization with the input waveform.
A random sampling oscilloscope is described, e.g., in Frye, G. and Nahman, N. S., “Random Sampling Oscillography,” IEEE Transactions on Instrumentation and Measurement, March 1964, pp. 8-13. In the random sampling oscilloscope, samples of the signal waveform amplitude are extracted at random points in time with respect to the start of the signal waveform. The time position, with respect to the start of the signal waveform, of a given amplitude sample is determined by measuring the elapsed time occurring between the start of a given cycle of the signal waveform and the random collision between the signal and the sampling pulse. An input trigger circuit is required which is capable of precisely detecting a predetermined trigger level on the input waveform and which initiates the start of a horizontal time ramp generator at time t0. A free running periodic sampling pulse arrives at some time t0+t1, and a sample is immediately taken of the signal amplitude at the time t0+t1; this information is stored in a vertical memory. The sampling pulse is also passed through a delay td to the horizontal time ramp generator. The arrival of the delayed sampling pulse stops the excursion of the horizontal time ramp at t0+t1+td. Then the maximum excursion of the horizontal time ramp is stored in a horizontal memory. Therefore, two pieces of information are now stored in memory, a) the instantaneous amplitude of the signal at the moment the sample pulse arrives; and b) the time position t0+t1 plus a constant delay time td. After the memories are read, the memories are reset, and the system is ready for another initiating trigger pulse. The time resolution and accuracy of this technique is extremely limited by the speed and linearity of the horizontal time ramp, and the accuracy of starting and stopping the horizontal time ramp generator. In addition, this technique is further limited by the necessity to trigger the horizontal time ramp generator in synchronization with the input waveform.
U.S. Pat. No. 5,162,723 issued Nov. 10, 1992 to Michael S. Marzalek, Richard C. Keiter, John A. Wendler, Stephen R. Peterson, Ronald J. Hogan describes a sampling signal analyzer. The sampling signal analyzer comprises a means for synthesizing a sampler drive signal. Sample timing is based on the intermediate frequency signal produced by the sampler. The intermediate frequency can be an arbitrarily low frequency, which allows digitizing and digital signal processing. However, the intermediate frequency requires low pass filtering to reject intermodulation products generated in the sampling process. The low pass provides a means for bandwidth limiting the intermediate frequency signal before analog to digital conversion takes place. In accordance with the disclosure in this patent, the frequency of the input waveform is initially ascertained, an appropriate sampling frequency is then determined, data needed to reconstruct the input waveform is acquired, and the input signal wave shape is reconstructed for display. Although this invention has an advantage over prior art in that it is not triggered directly in response to the level of the input signal to be measured, the disclosed architecture has many disadvantages. The phase noise of the sampler drive signal source is a significant limiting factor when measuring signals to 40 Ghz. The sampler drive signal frequency resolution is in the order of 0.001 Hz and is not sufficient for coherent sampling of pseudo random binary sequences. Pseudo random patterns do not appear in the same position on the display screen from sweep to sweep unless a recovered clock is used as a trigger source. The frequency response of this instrument is limited to 20 GHz without software corrections and to 40 GHz with software corrections. However, software corrections cannot always be applied e.g., when measuring eye diagrams. In the disclosed invention the clock frequency of the vertical channel analog to digital converter circuit is the same as the sampler drive frequency. The sampler drive frequency is from 10 MHz to 20 MHz, a very low frequency for accurate microwave and millimeter wave sampling above 20 GHz, and unfortunately too high a frequency to clock a high resolution analog to digital converter. For this reason, this architecture suffers in frequency response, and in vertical dynamic range of only 10 bits. The step recovery diode pulse generator is physically removed and shared between two sampler circuits. Because of the interconnect and loading, the pulse generators harmonic content can degrade. The sampler is of a known type comprised of two diodes and a balun. The parasitic capacitance of two diodes introduces substantial loading on the input port. Furthermore, the frequency response of the balun can effect the pulse generator's harmonic content. The foregoing disadvantages contribute to limiting the disclosed inventions frequency bandwidth to 20 GHz and the dynamic range to 10 bits.
U.S. Pat. No. 5,631,553 issued May 20, 1997 to Tapan K. Bose and Raymond Courteau describes an RF vector analyzer based on synchronous sampling. In this apparatus the sampling strobe synthesizer is physically removed and shared between all of the sampling gates. Because of the interconnect and loading, the sampling strobe synthesizer's harmonic content can degrade. The sampling gate is in the form of a four diode bridge and the sampling strobe synthesizer is introduced to the bridge through a differential transistor pair and an isolation transformer. The use of a four diode bridge, a differential transistor pair, and an isolation transformer severely restricts the bandwidth of this sampler. The sampling strobe synthesizer requires a time i
Frommer William S.
Frommer & Lawrence & Haug LLP
LeCroy Corporation
Metjahic Safet
Polito Bruno
LandOfFree
Waveform translator for DC to 75 GHz oscillography does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Waveform translator for DC to 75 GHz oscillography, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Waveform translator for DC to 75 GHz oscillography will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2475283