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EDA Software Design Flow Considerations for the RF/Microwave Module Designer

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EDA Software Design Flow Considerations for the RF/Microwave Module Designer Cadence is a pivotal leader in electronic design and computational expertise, using its Intelligent System Design strategy to turn design concepts into reality. Cadence customers are the world's most creative and innovative companies, delivering extraordinary electronic products from chips to boards to systems for the most dynamic market applications. www.cadence.com © 2021 Cadence Design Systems, Inc. All rights reserved worldwide. Cadence, the Cadence logo, and the other Cadence marks found at www.cadence.com/go/trademarks are trademarks or registered trademarks of Cadence Design Systems, Inc. All other trademarks are the property of their respective owners. 15701 01/21 DB/SA/WP-RDR-SYS/PDF What's Ground? For MMICs with semi-insulating substrates and backside metallization, it is common to model on-chip interconnects as microstrip. Traces on the topside of the semiconductor are considered to be quasi-transverse EM (TEM), propagating struc- tures with electric fields maintained between the trace and the backside metallization. Interpreting this within the concept of ground as a current return path, signals launched on the chip bond pads have their return current flowing along the backside metallization. The backside metallization is considered ground during the chip design and thus forms the reference for all other uses of ground. However, ground for the included module chips and module circuitry then becomes the ground plane, pours, or (larger) traces on the board. The reference for the returning current for a signal on the board, which just happens to go up onto a MMIC and back onto the board, is the ground plane on the board. Thus, any chip interconnect that was modeled as a microstrip is now using the wrong ground because the reference has changed. Fortunately, the AWR Design Environment platform offers several ways to handle this situation. For a simple two-port device, the symbol representing the chip can have an explicit ground connection created simply by modifying the SUBCKT repre- senting the instance of the chip on the board. This will automatically and identically change the reference for all the ports/ pins on the SUBCKT. If individual pins have different paths from the chip ground to the module ground or there are more than two pins, then a transformer can be used at each chip bond pad to transform the chip ground to the module ground. Any explicit grounds in the chip schematics will also need to be transformed to the module ground. Baluns can also be used in a manner similar to the transformers. Chips not on semi-insulating substrates with backside metallization will have more complex ground schemes to begin with because the majority of the current flowing back through the topside ground pads will have more complex electric field arrangements. Assuming that these have been captured in the chip design or extractions, they should be similarly re-refer- enced to the module ground using transformers or baluns. Similarly, with module ground, if there is no definitive ground plane in the board or if ground pours are electrically far away from the chip, then the actual current return path may be difficult to ascertain directly. Oftentimes, if this is the case, the design will have some severe performance issues, which can be addressed by a proper understanding of signal propagation and its modeling using advanced EM tools. In any event, getting ground right on the chip and then again on the board is one of the keys to a repeatable and successful module design flow. Conclusion MCM technology is an important facet of modern electronic miniaturization and microelectronic systems and will continue to grow as demand escalates for smaller, cheaper, and faster electronic devices. While MCM technologies offer superior perfor- mance for complex RF and microwave applications, the challenge for designers is to integrate multiple components on a single chip while overcoming the electrical and mechanical issues associated with each individual component. This white paper has described the steps that can be taken with AWR Design Environment platform of tools to successfully implement an integrated design flow for an MCM MMIC design, using as an example a 2.5GHz GaAs MMIC PA module along with a microwave laminate module to form the output match. The AWR software unified database approach to EDA, the high degree of automation and intuitiveness, and the multiple EM technologies offered simplify the design process and save designers substantial amounts of time, a precious commodity in today's competitive marketplace. From streamlining the process of synchronizing the schematic and layout, to enabling multiple technologies within a design, to EM simulation, automated extraction, and verification from within the schematic, the AWR Design Environment platform offers innovative technologies to get the job done faster and more accurately.

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