Appliance Design - February 2009 - (Page 38)

SHIELDING & EMI Fig. 13. Test setup, amplifier input filtering for GSM noise. Fig. 14. Data plots, GSM noise suppression. 416 conventional capacitors, which reduced I/O plane peak-peak noise to 283 mV. 416 X2Y capacitors, which reduced I/O plane peak-peak noise to 100 mV. To achieve the same peak-peak noise reduction so that component replacement ratios could be quantified, additional conventional capacitors were added and periodically measured until peak-peak noise equivalency was achieved. Peak-peak noise was finally reached when 58 conventional capacitors were used around the FPGA. The results of the test showed that 16-X2Y capacitors either reduced conventional capacitor count by 73 percent and eliminated drilled vias by nearly 60 percent, or reduced peakpeak noise by 3:1 noise reduction when compared to 16 conventional capacitors. Noise susceptibility In the not-to-distant past, home appliances with multiple functions that interacted with people seemed like a fantastic premise. But today’s appliances often incorporate multiple functions, such as refrigerators that contain entertainment devices such as a built-in stereo or LCD televisions with embedded speakers. In addition, wireless phones have proliferated and many people, especially the younger generation, have grown up carrying cell phones from morning to night, much like a wallet. (See Fig. 12.) But wireless telephones can also gen38 applianceDESIGN February 2009 erate EMI that disrupts susceptible kitchen appliances. EMI problems can occur when a cell phone is in close proximity to appliances with embedded speaker systems. An example of one such EMI problem is GSM cell phone buzz. Coherent highfrequency noise from GSM cell phones can alias to low frequencies. The “buzz” is caused by the phone transmitter pulsing at a repetition rate of 217 Hz during a call, the 217-Hz signal is harmonic-rich; it can result in an audible buzz in television or stereo speakers when coupled into amplifier circuitry. Because cell phones operate in multiple high-frequency bands, a broadband, lowinductance filter solution is needed. To demonstrate the effectiveness of X2Y capacitors in eliminating audible GSM buzz, a test was set up in X2Y’s metrology lab consisting of a GSM handset secured to a 900 MHz antenna on shielded coax attached to an amplifier circuit board placed inside a shielded enclosure. A power divider delivered the cell phone’s offending signal to the positive/negative amplifier inputs. Conventional and X2Y capacitors were applied at the amplifier’s input and power pins. A spectrum analyzer was connected at the amplifier output for comparative measurements. (See Fig. 13.) The test showed that X2Y provided a nearly flat response above the ambient, was typically 12 dB below the no-filter result, and provided 4 dB to 10 dB better rejection than the conventional MLCC filter. X2Y successfully eliminated GSM buzz [11]. (See Fig. 14.) These tests, along with current applications in the field, have proven that low inductance, three-node X2Y capacitors can be used for noise suppression in products that need to meet EMC compliance. By efficient design, X2Y capacitors can replace multiple passive components to improve circuit performance and lower assembly costs. X2Y Attenuators is an intellectual property developer that has licensed the X2Y capacitor technology to a number of passive component manufacturers. < For more information, visit: www.X2Y.com References: [1] Accurate capacitor inductance extraction from s21 measurements. [2] Noise Reduction Techniques in Electronic Systems, 2nd Edition, by Henry Ott. [3] GTEM cell simplifies EMC test. [4] Broadband testing of low cost solutions for DC motors. [5] EMI Design Techniques for Microcontrollers in Automotive Applications. [6] Schurter 5150 Series IEC inlet. [7] Altera in home appliances. [8] Howard Johnson. [9] Steve Weir, Teraspeed Consulting, LLC. [10] X2Y live FPGA power bypass. [11] Cell phone GSM interference. www.applianceDESIGN.com http://www.X2Y.com http://www.appliancedesign.com

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Appliance Design - February 2009 Contents Editorial Shipments/Forecasts News Watch Force-Sensing Technology Offers Designers an Alternative Approach to Creating Touch-Control Interfaces A Flammable Vapor Sensing Technology that was Originally Developed for use in Water Heaters has Evolved for use in a Broader Array of Applications Latches, Hinges, and Slides Must Reliably Secure Parts Together, Sometimes for Hundreds of Thousands of Cycles. Beyond their Utilitarian Functions, They Can Also Change Consumer Perceptions Elastomeric Electrical Connectors Can Solve Space Constraint Problems in Electronic Products and Provide Some Cost Advantages as Well A Multi-Layer Ceramic Capacitor with a Novel Electrode Design Can Suppress Electromagnetic Interference, Improve Circuit Performance, and Reduce the Number of Needed Components Design Marts Association Report: AHRI Advertisers’ Index

Appliance Design - February 2009

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