Conformity Magazine - October 2007 - (Page 30)

waveforms. There are always “parasitic” circuit elements that are needed to create the specified waveforms. The deviation of the waveforms from the waveform predicted by the simple schematics is on purpose. All real world test systems have parasitics that can not be avoided. Standards must reflect systems that can be built in the real world. The machine model has a very similar circuit diagram as HBM, and is shown in Figure 1. The capacitor value is increased to 200pF, and an approximately 0.8µH inductor replaces the 1500Ω resistor from HBM. The inductor is not specified in the standards but is needed to produce the required oscillatory MM waveform. Figure 3 shows an actual, in specification, waveform for MM. Note that, even though the charging voltage for the waveform shown in Figure 3 is a tenth that of the HBM example, the peak current is considerably higher. CDM is substantially different from HBM and MM. There is no capacitor even nominally specified in the standard. This makes sense because the CDM discharge simulates a charged integrated circuit being discharged to a metal surface. The capacitor is the device’s capacitance to its surroundings. There are several charged device test methods, but one of the most popular is the Field Induced CDM (FCDM). A simplified diagram of a field induced CDM tester is shown in Figure 4. Figure 1: Basic circuit diagram for HBM and MM gital Ed 1-2h circuit diagram for HBM is shown in Figure 1. An actual HBM current waveform is shown in Figure 2. Note that a characteristic of HBM, and of all ESD standards, is that the ESD stress is specified by a current waveform into a defined load. The compliance of the waveform to the standard is determined by waveform parameters, such as peak current, rise time, percent ringing and decay time. The values of the resistors, capacitors and inductors in the circuit diagrams are in fact not specified in the standards; only the current waveforms, and only “nominal” values for the circuit elements are in the standards. Another feature of all of the standards is that the basic circuit diagram presented for the model will not produce the specified 9/18/07 1:52 PM Page 1 Another Step Forward View every page of Conformity magazine digitally. That includes every article, every NewsBreak, every ad, everything you’ve come to expect from Conformity, The Integrated Authority on EMC Compliance and Design. � View every page of Conformity as it appears in print. View advertisers’ web sites with one click. Print pages. Save an offline version to your desktop. Send the digital issue to a friend via e-mail. READERS: Sign up to receive your digital edition at www.conformity.com. ADVERTISERS: To participate in the digital edition call 978-486-0888 30 Conformity oCtober 2007 � � � � www.conformity.com http://www.conformity.com http://www.conformity.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - October 2007

Contents Editor’s Note Commission Proposes Changes for 57-64 GHz Spectrum Rules FCC Continues Actions Against Jamming Device Distributors Radio Operator Fined for Failing to Make Equipment Available for Inspection Commission Fines Unsolicited Fax Advertisers Firm Offering Quality Standards Training Also Fined Breaking New Ground with Lithium-Battery Generic Requirements for Use in Telecommunications Facilities ESD Open Forum EMC UK 2007 Conference Set Staying Abreast of U.S. E-Waste Legislation EU Commission Establishes RFID Expert Group Update on China's CCC Compliance Program System Level ESD Testing: The Waveforms An Alternative Approach to Surge Suppression Testing Equipment Buyer's Guide EU Scientific Committee Releases Updated Data on EMF Risks Updated Standards List For The EU’s EMC Directive Updated Standards List For The EU’s Directives on Measuring Instruments Call for Presentations for 2008 International ESD Workshop Announced CPSC Actions In The News IEC Standards Update Product Reviews UL Standards Update New Products From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - October 2007

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