Conformity Magazine - June 2008 - (Page 45)

In Figure 4, the HDMI system designer must route around and under packages, creating unequal trace lengths and introducing additional parasitic capacitance along the trace due to routing under multiple packages. The solution in Figure 5, which is now available from several vendors, eliminates these problems by matching the signal and ground return pins directly to the pins on the connector, using the same spacing and pin assignments. When considering the multi-channel device, consider the effective pin pitch of the entire solution. An MSOP device may have 0.5mm pitch pins, but when total body width and power/ground pins are considered, the effective pin pitch of two packages grows to slightly larger than 0.5mm, and some fanout of the pairs must be done, using additional board space. Very often, a “large” 8-channel package takes up less board space than two 4-channel or four 2-channel devices. Summarizing capacitance issues: • Lowering capacitance of the ESD circuit is important for • Matching capacitance can be as critical as having low capacitance, since mismatched capacitance can cause signal skew and EMI problems; signal integrity, but care should be taken to ensure that the device can still provide adequate ESD protection; • When possible, choose a semiconductor-based ESD device (best performance) in a package that allows simple straight-through routing, minimizing trace length mismatches, reflections, and skew. Impedance Matching and Other Design Compensation Issues Regardless of how low the capacitance of an ESD device is, there is going to be some level of signal distortion introduced by any device added to a signal line. At GHz transmission frequencies, even small amounts of capacitance can be a problem. Figure 4: HDMI TMDS routing using 8 single channel devices in SOT-23 packages Figure 5: HDMI full port routing using single 12-channel CM2021-02 device JUnE 2008 Conformity 45 http://www.citelprotection.com http://www.citelprotection.com

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Conformity - June 2008 Contents Editor's Note 700 MHz Auction Raises a Record $20 Billion FCC Modifies PCS and AWS Power Limit Rules for Broadband Wireless Commission Designates Spectrum Test Bed FCC Releases Report on Wireless Competition Commission Proposes $5 Million Fine for Slamming Using EDX for Non-Destructive Detection of Lead in Consumer Products ESD Open Forum Challenges in Testing - Improving Election Security and Accuracy Part 1 Challenges in Testing - Human Body Model: The Hidden Challenges High-Speed Signal Integrity Considerations for ESD Components Focus On...EMC Components Buyer's Guide FCC Levies $2.6 Million Fine for Junk Faxes FDA Updates Guidance on its Product Review Process EU Issues Updated Energy Star Regulations EU Repeals Directive on Veterinary Electro-Medical Equipment New Product Announcements Updated Standards List for the EU's PPE Directive CPSC Announces New Effort to Keep Out Hazardous Products CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity - June 2008

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