Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-05-06
2001-07-31
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S501000
Reexamination Certificate
active
06268738
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of and apparatus for high-speed scanning of printed electromagnetic field levels and is particularly concerned with testing circuit packages and like devices.
BACKGROUND OF THE INVENTION
An important tool in circuit board design is the ability to easily and accurately locate and measure electromagnetic emissions from an operating circuit board. The prior art electronic emission monitors are represented by Canadian Letters Patent 1,286,724 assigned to Northern Telecom Limited, granted on Jul. 23, 1991; U.S. Pat. No. 4,829,238 granted on May 9, 1989; U.S. Pat. No. 5,006,788 granted on Apr. 9, 1991; and, U.S. Pat. No. 5,218,294. These patents describe a method and apparatus for monitoring electromagnetic emission levels from operating printed circuit boards.
The prior art enabled the user to carry out two types of scans: spectral, that is, signal strength relative to the frequency of the scanner, and spatial, that is, signal strength relative to the position of the signal on the printed circuit board. The spectral scan retains only the highest value observed at each frequency point, regardless of the probe, and the display is, therefore, merely a profile of peak electromagnetic amplitudes plotted against frequency. All other readings are discarded. A spatial scan takes a reading of the signal level at the designated frequency, for each probe within the selected scan area. The scan results are retained in a display file which provides a color coded map of the current flows (signal strength) in the scan area at the defined frequency. The amount of time required to complete the scan is in the range of 95 seconds.
The disadvantages and limitations associated with the prior art apparatus relate to the fact that it cannot scan the board under test fast enough for use in production line testing. To be effective in such an application requires an method and apparatus for gathering spectral information from all locations of the printed circuit board under test in much less than one second.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved method and apparatus for monitoring electromagnetic field levels from printed circuit board.
In accordance with an aspect of the present invention there is provided an apparatus for testing a device for electromagnetic field therefrom, the apparatus comprising: probe means positionable in a plurality of predetermined positions immediately adjacent to the device, said predetermined positions having a known spatial arrangement; addressing means for successively addressing the probe means at each predetermined position; a receiver connected to said addressing means for measuring current induced in the probe means by electromagnetic field from respective immediate adjacent regions of the device under test; signal processing means for analyzing electrical outputs from the probe means to obtain a measure of electromagnetic field levels immediately adjacent the device under test associated with each predetermined position; spectrum analyzer means to gather and analyze spectral information; digital computing means to convert the analog output of the spectrum analyzer means to a digital output; calibration means to calibrate the digital output.
In a further embodiment of the present invention, the spectrum analyzer output is connected to an analog to digital converter via the “video out” output socket.
In yet another embodiment of the present invention, the initial analog to digital conversion is triggered to start the sweep of the printed circuit board under test by the electromagnetic scanning apparatus thereby synchronizing the operation of the device under test with the scanning apparatus allowing the collection of scanning data with respect to time.
In an embodiment of the present invention, a spectral scan of the device under test is obtained resulting in a display of the profile of peak amplitudes plotted against frequency. Several peaks are chosen by the computer system and the frequency of each peak is recorded. From the frequencies of these peaks, a piece wise linear frequency calibration curve is produced.
Another aspect of this invention is directed to a method of high-speed scanning of electromagnetic field levels comprising the steps of: placing a device under test immediately adjacent to a probe means which comprising a plurality of probes, each probe having a predetermined position within the probe means; addressing a first probe of the plurality of probes, then synchronizing a spectrum analysis sweep to commence at the same point in time of the activity of the device under test; measuring electromagnetic field levels from the device under test as detected by the first probe, and, using a spectrum analyzer, sweep across a desired frequency range generating a video output signal; digitizing this video output signal, level calibrating the digitized video output signal and saving the individual data so obtained. Furthermore, these steps can be optionally repeated for each probe of the plurality of probes as required and the steps between the individual data of the digitized data set frequency calibrated, and optionally waiting one sample time more, followed by repeating the above steps for each possible sample time for each probe of the plurality of probes, and displaying the calibrated data set.
In another embodiment of the present invention a method is provided whereby measured level of electromagnetic radiation from the device under test is calibrated. The “Cal Out” output of the spectrum analyzer is serially connected via an attenuating means of 40 dB to the spectrum analyzer input.
Particularly for testing a device for electromagnetic field therefrom, the apparatus can further include a memory at which circuit layout design data is stored, and means for inputting said circuit layout design data to the controller means, said controller means being operable to generate a circuit layout map from the circuit layout design data and said display being means operable simultaneously to display said map of electromagnetic field level measures and said circuit layout with said maps superimposed.
In accordance with the present invention, a spectral analyzer is placed in series with the electromagnetic probe array.
In accordance with another embodiment of the invention, the “video out” terminal of the spectral analyzer is connected to a high speed analog to digital (A/D) converter.
By using a spectral-spatial scan, the present invention seeks to overcome the disadvantages found in the prior art. The use of a spectral-spatial scan makes it possible to measure electromagnetic fields from devices under test orders of magnitude faster than prior art scanner apparatus. The increased scanning speeds enable the user to build large data structures of scan data. In addition, the systems provide powerful manipulative, comparative and analytical tools which allows multiple perspectives of the scan results, thus establishing a new level of visualization capabilities.
A further objective of the present invention is to provide a device of the character herewithin described which permits the production of improved products; significantly reduces pre-compliance times with a consequent reduction in the time to market of the device under test; reduced re-engineering or modification costs; cost effective means for ensuring on-going electromagnetic field compliance with preset standards; and, minimized life-cycle costs for the product. The spectral-spatial scan system provide a low cost, automated, non-contacting, testing of a devices quality and a testing of their performance on the manufacturing line.
REFERENCES:
patent: 4829238 (1989-05-01), Goulette et al.
patent: 5006788 (1991-04-01), Goulette et al.
patent: 5028866 (1991-07-01), Wiese
patent: 5218294 (1993-06-01), Soiferman
patent: 5300879 (1994-04-01), Masuda et al.
patent: 5424633 (1995-06-01), Soiferman
patent: 1286724 (1991-07-01), None
patent: 2161292 (1997-04-01), None
patent: 0 239 251 A3 (1987-09-01), None
pate
Gunthorpe Gary E.
James Don E.
Emscan Corporation
Gardner Groff Mehrman & Josephic P.C
Mehrman Michael J.
Nguyen Vinh P.
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