Microwave Engineering Europe - March 2008 - (Page 26)

26 EDA — CIRCUIT EXTRACTION Figure 3: Distributed ampliﬁer with ACE to extract distributed and discontinuity models with no interconnect couplings. Extraction time is ~ 0.5 seconds for DC to 12 GHz. the accuracy of EM and the speed of closed-form models) can be used for discontinuities. For the most accurate answers, designers can direct the ACE tool to use models that have FEM solvers built right in with the model that are highly optimized to solve that particular geometry. GFMCLIN, for example, has an FEM solver inside, which turns the parametric descriptions into geometries solved by its FEM solver in a fraction of the time of generalized, three-dimensional (3D) FEM tools. Designers can now choose to trade off the difference between speed and degree of accuracy when they select the ACE MoM solvers, which are faster than the FEMbased circuit models such as GFMCLIN and more accurate than the closed-form models such as M2CLIN. Example 1 – MMIC distributed ampliﬁer A monolithic microwave integrated circuit (MMIC) distributed ampliﬁer depends upon the inter-stage interconnects to deﬁne its impedance and bandwidth characteristics. Figure 4 shows such a design using pseudomorphic high electron mobility transistor (PHEMT) technology, initially modeling the interconnects with distributed MLIN, MBEND, MTEE, etc. models, but, for example, no coupling among adjacent arms of the meandered inter stage lines. Using ACE software with a very large coupling distance speciﬁed yields greater bandwidth, but at the expense of gain ﬂatness; the culprit is the couplings, shown in extracted schematic form in Figure 3. By reducing the ACE coupling distance, it can be seen that majority of the detrimental coupling is due to the adjacent arms of the meandered interconnects highlighted in Figure 5. In a matter of minutes, the ACE technology empowers the designer to identify, pinpoint, and redesign the circuit as appropriate, whereas iterating cycles with layout and EM analysis would likely take the better part of a day or days. RF-style Interconnects: iNets In the above example, the interconnects and meander lines were drawn from a microwave engineers point of view — explicit MLIN’s, t-junctions and MBENDS. With just a little more effort, the parallel segments could easily be changed to coupled-line models and similar results obtained without the need for ACE. To leverage the real beneﬁt, AWR provides its unique iNet technology. This technology enables the designer to draw a Figure 4: ACE software with large coupling distance showing performance degradation. Extraction time is approximately 1 second for DC to 12 GHz. Figure 5: Reduced ACE coupling radius (bold traces, left) reveals overall performance degradation (gray traces, left) mainly due to adjacent couplings (red circles, right). Microwave Engineering Europe ● March 2008 ● www.mwee.com 024_025-026-028-029_030_MWEE.ind26 26 21/02/08 11:08:34 http://www.mwee.com

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Microwave Engineering Europe - March 2008 News Contents Comment Wireless Infrastructure: A Direct Conversion I/Q Demodulatordrives Favorable Basestation Cost-performance Metrics Wireless Infrastructure: Mobile World Set to Reshape the Internet RF Amplifiers: Latest Advances in RF Amplifiers Include a CMOS PA Operating at 77 GHz and Significant Advances in PAs for WiMAX and Broadband Applications Many Applications Still Require Unique Performance Benefits of BeO ACE Automated Circuit Extraction Returns to Real Design by Exploring Design Alternatives and Changes in Seconds Exceeding the Standard for Wireless Sensor Networks Products Calendar

Microwave Engineering Europe - March 2008

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