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Unformatted text preview: 1 The Ground Conundrum Assignment: Find and research papers on this subject, be prepared to defend research The Ground Conundrum 2 Grounding Thoughts Ground is only a convenience for a voltage measurement reference The ground paradox Ground is 0 volts Ground is relative There is not an absolute ground Ground can be anywhere Any sources referenced to ground returns power to ground All real sources have a reference to ground The Ground Conundrum 3 Reduced Ground Definition The reason for the reduced ground concept is related to the modeling of transmission lines in any spicelike simulator. We will develop the concept of reduced ground first and subsequently illustrate why it is required. The reduced ground: Collapses return path circuits to a single reference node. Signal measurement accuracy of a network is then preserved by incorporating the return path effects as elements added into the signal path. Measurement of ground bounce is hidden. Return path may be power or ground. We will only concern ourselves with ground for now. Reduce Power is a good research and development topic. The Ground Conundrum 4 First Order View  Resistor Model This Simple model will be sufficient to illustrate the ground reduction concept and issues of creating multiline reduced models I1I1 I2I2 I1I1 Lets simplify a strip to simple resistors Signal path Return path The Ground Conundrum 5 The lossless return path Calculate voltage at the load as a reference R_source=50 R_tline=2 R_load=50 2V The Ground Conundrum 6 The lossy return path Calculate the voltage at the load Notice this is less that the voltage on the previous slide because the return path is considered here. Now lets use this voltage a reference The goal is to create a circuit that produces the same load voltage and current but only has one ground node. R_source=50 R_tline=2 R_load=50 2V Rg_tline=2 The Ground Conundrum 7 The reduced ground circuit Thevinize the ground resistor into the signal path. Both lossy ground circuit and the reduced ground circuit produce 0.9615 volts at the loads. One ground node The Ground Conundrum 8 R_source=50 R_tline=2 R_load=50 2V R_source=50 R_tline=2 R_load=50 2V Rg_tline=2 Rg_tline=2 Add another line! Lets keep with a resistor model and a reduced ground path Spice only allows a single node for return path for multi conductor transmission line element. I2I2 I1I1 I3I3 I4I4 Tline model: 2 lines plus return in 2 lines plus return out This seems OK so far but consider I1, I2, I3, and I4 are combined The Ground Conundrum 9 9 Take a closer look at where the current are and the voltages are developed Z1 Z2 Z1g Z2g Z12g Z12 Theres can be a voltage drop between these two nodes Current in plane It is possible to collapse both ground nodes into one node but that creates issues The Ground Conundrum...
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 Spring '03
 YinchaoChen

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