Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-02-19
2004-03-02
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S750010, C324S763010
Reexamination Certificate
active
06700388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to measurement of electromagnetic interference (EMI), and more particularly to high-precision automated techniques for testing and reporting EMI emissions from radiating objects.
2. Description of the Related Art
Electromagnetic interference (EMI) from radiated emissions and from conducted emissions is problematic in a wide variety of contexts. For example, power transmission lines may convey transient surges or other voltage irregularities to electrical equipment intended to be powered therefrom, such that equipment in line therewith may cause an interference to an intervening electrical bus and to the power lines themselves. This interference may compromise computer performance, television picture quality, or the functioning of other electrical equipment powered from such lines. Electromagnetic energy radiated from the equipment itself often causes severe, undesirable effects which range from poor signal quality or poor reception in radios and televisions, to complete ineffectiveness or inoperability of electronic devices.
Electronic devices, most notably electronic communication devices, typically emit some amount of undesirable EMI. These emissions may be a concern for a number of reasons. EMI emissions can potentially interfere with devices communicating in the same frequency band. As the frequency spectrum available for communications becomes increasing crowded to meet demands for wireless communications, the importance of minimizing EMI emissions from individual devices becomes more critical. Presently, for example, U.S. Federal Communications Commission (FCC) requirements mandate that every cellular communications telephone be tested to certify EMI performance. Similarly, certain telecommunications equipment for government or military applications require strict conformance to military emissions standards.
More rigorously, EMI can broadly be divided into two main categories: natural and man-made. The former is due to atmospheric effects and can be divided into low frequency electric and magnetic fields and high frequency electromagnetic fields. The source of man-made interference is due to radio transmitters, including harmonics and spurious frequencies resulting from mixing intermediate frequencies, electroheating elements (microwaves) and digital computational devices increasingly being used in radio transceivers. Classes of interference which are specifically regulated in radiowave transmission devices include harmonics and spurious interference. For example, military standards (MIL-STD-261 E) require the following suppression:
Transmit Harmonics:−50 dBc for 2
nd
and 3
rd
, −80 dBc for all others
Transmit Spurious:−80 dBc,
where dBc is the interference power referenced to the carrier, i.e., the 2
nd
and 3
rd
harmonics must be 50 dB below the carrier at the antenna output. The spurious outputs are produced by intermodulation products in the IF path (for both receive and transmit).
Another concern is that electromagnetic energy radiated or conducted from electronic devices, including EMI emissions, generally contains information, which may be extractable by unintended parties. In particular, certain electronic devices not designed to emit electromagnetic signals (e.g., personal computers and conventional telephones) or designed to emit only short-range signals may nevertheless emit significant EMI signals detectable at some distance from the device. For security reasons, such devices may require certain shielding in order to prevent such devices from emitting radiation in a manner that allows an individual monitoring the emitted radiation to discern intelligible information regarding the content of the communication. Such concerns are particularly relevant to government or military systems and devices. Moreover, with the rising specter of commercial espionage and its harmful impact on commercial businesses, industries within the private sector are also placing increased emphasis on EMI testing.
To ensure compliance with EMI requirements, EMI testing is performed in a wide variety of commercial and military contexts. Currently, EMI certification is highly manpower intensive. Analysts often conduct tests literally by hand, with little or no process automation. This situation is quite similar to that faced by surveillance personnel over the last forty years where surveillance analysts in signal intelligence activities (SIGINT) spend countless hours examining monitors in an attempt to identify by sight and/or sound, signals of interest. On a reduced scale, fields of radio astronomy, as well as geophysics and biomedicine, also encounter similar manpower-intensive signal testing.
Presently, EMI testing of electronic devices is generally performed using analog equipment. Basically, a conducted or radiated signals is detected by means of an antenna attached to an analog radio frequency (RF) receiver, and the peak voltage of a time domain signal is registered (by hand) and compared to a mask or threshold provided by various standards (e.g., military or commercial standards). If the peak voltage exceeds the threshold, the electronic device(s) under test is said to fail the specific test.
These tests are generally conducted at different bandwidths in a total span of 1 GHz. More specifically, two different types of tests are conducted; a broadband scan test and a narrowband scan test. In the broadband scan, the peak voltage is measured in a 100 kHz bandwidth. In the narrowband scan, different bandwidths are selected and range from 0.5 kHz, 1.0 kHz, 5.0 kHz, 10 kHz, 25 kHz, 50 kHz, 75 kHz and 100 kHz. This process is repeated through each 100 kHz bandwidth in the total 1 GHz bandwidth.
For example, consider a conventional EMI test involving analysis of a 1 GHz bandwidth in segments of 1 kHz. The process requires assessing the signal bandwidth in 10 kHz segments looking for spurious 1 kHz tones which are audio identified by an analyst. The next step is to measure the amplitude of the audio tone, which is done by reconnecting the system (i.e., reconnecting cables). An experienced analyst can analyze between three to seven segments per second, not inclusive of the time required to measure the amplitude of detected signals; consequently, the time required to analyze the entire 1 GHz bandwidth can be on the order of eight hours and is highly susceptible to human error. Long testing times increase the duration of product development cycles and increase unit production time and cost, potentially impacting timely delivery of products.
Moreover, such a process requires expensive analog equipment, given the number of filters which have to be applied at the front end to select each one of the different bandwidths. Furthermore, each bandwidth scan has to be run separately and there is no permanent record of the final reading (i.e., the comparison with the mask or threshold). Thus, analog testing does not provide a “history” of testing that can be later reviewed or referred to, and problems that arise during testing typically have to be solved over and over again, since only the memory of analysts can be relied upon to recall and address testing problems.
Accordingly, it would be highly desirable to implement an automated approach to EMI testing using digital signal processing techniques for detecting, analyzing, identifying, and quantifying the amplitude level of EMI signals produced from a radiating body.
SUMMARY OF THE INVENTION
Therefore, in light of the above, and for other reasons that become apparent when the invention is fully described, an object of the present invention is to automate EMI testing using digital signal processing techniques to thereby eliminate the need for human observation of signals and resulting errors.
A further object of the present invention is to reduce the time required to perform EMI testing of equipment.
Another object of the present invention is to enhance the accuracy of EMI testing.
Yet a further object of the present invention is to reduce the number
Lagrow David W.
Mayor Michael A.
Edell Shapiro & Finnan LLC
ITT Manufacturing Enterprises Inc.
Teresinki John
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