The Spice-compatible Rf Transmission Line Modeling

On-chip interconnect acts as RF transmission line at RF and microwave frequency, so it must be considered and researched as RF transmission line. Frequency-dependent resistance and inductance restrict the use of its model under transient analysis of SPICE circuit simulator. Accordingly the research of SPICE compatible RF transmission line model is practical for IC development.Based on the physic characteristic of on-chip interconnect and the analysis of microwave transmission line theory and classic interconnect model, the parasitical effects of interconnect are modeled: PEEC is used to model skin effect and proximity effect; substrate magnetic loss is equal to image current by complex image theory, the calculations of skin effect, proximity effect and substrate magnetic loss are combined. Obtained is the frequency-dependent RF transmission line model of interconnect. Analyzed and compared are the two structures which can eliminate frequency- dependent characteristic. The shunt structure is used to get the frequency-independent model which is SPICE compatible.The skin effect's impact on series resistance Rs and series inductance Ls is calculated and analyzed. The impact of different substrate conductivities on Rs and Ls is shown, larger conductivity has larger impact.From DC to 20GHz, the obtained single interconnect model and classic model without substrate loss is calculated by MATLAB. Compared with HFSS, the error of the obtained model is 8%, which is better than 20% of the classic model. The two interconnect model shows 10% error to HFSS.Finally a 2.4GHz class-A power amplifier is designed. From the practical technology parameters all the model parameters are calculated. The differences of output power and PAE with and without the interconnect model are obtained. The result shows that output power falls from 22.54dBm to 19.39dBm, PAE from 30.6% to 25.5%.