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JULY 2019 I DESIGN007 MAGAZINE 57 at both ends of the 50-mil fixture trace to gen- erate the S21 parameter. The S21 parameter of model 1A consists of the effect of interconnection inductance (i.e., point of interest) together with the 50-mil fix- ture trace (for the purpose of two-port shunt probing). To de-embed or remove the effect of the fixture trace, the standalone trace depict- ed in Figure 3 with the same dimension and height as in Figure 2 is modeled to generate its S21 parameter. The S21 parameter of the fix- ture trace is then split into two halves using the automatic fixture removal (AFR) as shown in Figure 4. Subsequently, S21 parameters of the two halves generated by PLTS-AFR and model 1A are imported to Keysight ADS to per- form de-embedding (Figure 5). The de-embed- ded S21 parameter that comprises the effect of decoupling capacitor and its interconnection inductance only is converted to impedance us- ing Equation 5. Equation 5: (Z = impedance of decoupling capacitor and interconnection inductance) The modeling and de-embedding procedures are repeated for model 1B and 1C with stitch- ing via height, h, of 7.95 mils and 13.95 mils, respectively. With reference to impedance plots shown in Figure 6, the three models ex- perience the same resonance frequency of 103 MHz. Across the wideband range, model 1A Figure 4. The S21 of the fixture trace is shown split into two halves. Figure 3: 3DEM structure of the 50-mil fixture trace to be de-embedded. Figure 5: Topology to de-embed fixture trace in Keysight ADS.

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