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PCBD-Apr2016

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60 The PCB Design Magazine • April 2016 transition which is 1/8 wavelength or larger can cause signal launch disturbances. However, for this same example operating at 3 GHz or 5 GHz, the 1/8 wavelength is 2.3 and 1.4 inches, respectively. The 0.3 inch transi- tion is now close to 1/8 to 1/4 inches in dimen- sion, which will have repercussions in the elec- tromagnetic fields at this transition and would need to be compensated for by the RF engineer. There are several things that can be done regarding the PCB and connector design to minimize the signal launch issue. One of the simplest ways is to use a smaller connector. In the RF industry, there are many different types of connectors and each type has a range of fre- quencies capable of being used with minimal electromagnetic field disturbances. The range of frequencies at which these connectors are rated are usually based on the connector not having resonances that interfere with the signal integrity, but in general, higher frequency-rated connectors are smaller. To show the relation- ship between connector size and frequency use, Table 1 lists some common connectors. When considering the details about signal launch, it can get pretty complicated. The elec- tric field transition from the connector to the PCB will have a change in the ground return path. There are isolated phase velocity differ- ences, small impedance variations, and often there are reflections and radiated energy. As more applications are moving to higher frequencies and higher speeds, signal launch is often misunderstood by designers who have worked at lower frequencies or speeds. This can be frustrating and it is recommended that the designer work with both connector and mate- rial supplier to try to find an optimized solution for the particular design. PCBDESIGN John Coonrod is a senior market development engineer for Rogers Corporation. To read past columns, or to reach Coonrod, click here. What is signaL Launch anD Why shouLD you care? Table 1. Connector size vs. cutoff frequency. network entertainment ap- plications are the stepping stone to a broader home Internet of Things (IoT) experience, even as consumers remain skeptical of the value proposition behind the home Internet of Things, wary of their cost and uncertain of their utility, according to a recent sur - vey of U.S. consumers by Interna- tional Data Corporation (IDC). About 28% of people who own a home network stream on- line videos to their televisions, and they are much more likely to express high interest in and adop- tion of home IoT applications than other home network owners. Moreover, one out of five peo- ple who use home automation, monitoring and control devices say their home IoT applications solved a problem they didn't know they had. Survey: Consumers Seeking Higher Value Proposition for Home Internet of Things

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