Printed Circuit Design & Fab - November 2008 - (Page 30)

MEASUREMENT AND SiMulation IMProvIng cIrcuIT SIMuLaTIon Real measurements allow the engineer to proactively improve the design, saving time and money. by BHAVESH MISTRy with the addition of real Measurements Shrinking timelines, budget constraints and the overwhelming need for rapid innovation challenge even the most battleweary and experienced engineer. But this is common in most industries. However, the ubiquity of electronics in modern life (imagine a world without laptops and cell phones) simply underlines this fact for those working in the Electronics Design Automation (EDA) industry. For engineers wanting to learn from others and the industry as a whole, the best way to approach design is through methodologies and successes that will enhance overall productivity. They quickly learn that at every stage of the circuit design flow (capture, simulation, layout, validation and fabrication), there is room to improve practices and to spend less time and money in design. Engineers have for sometime had circuit simulation as a tool to not only help drive better analysis of circuit decisions, but also to use that analysis earlier in the design flow. The idea is that if more time is spent improving the printed circuit board (PCB) design using simulation, time can be saved later through fewer prototype iterations and respins. Enabling simulation to be a true best practice, however, requires us to better bridge the gap between the world it emulates and the virtual interface. This article will show the true advantage in 30 simulation, particularly as we use everincreasingly complex models through real measurements. The Need for Simulation The backbone of electronics continues to be the PCB because it interfaces to various signals and external systems. Despite its varied use throughout the past 80 years, the PCB continues to require a high level of activity through iterative design attempts. The fact is that errors continue to be identified and, for many engineers, this results in the tedium of multiple prototype stages. As an engineer once mentioned, it is “offensive to his sanity” when having to continuously iterate on a design. These errors can be the result of a non-appropriate topology, or oversights in design decisions. Identifying these issues at the prototype stage means a return to the drawing board to correct the problem; this unfortunately leads to a major time and budget sink. Engineers need to avoid these iterations. Identifying errors before silicon meets copper translates into a quicker and more productive route to final product. Simulation Program with Integrated Circuit Emphasis (SPICE) allowed for the modeling of circuit devices to help provide more in-depth understanding of board-level (and IC) designs. Parasitics of the design can be realized and accounted for, providing a tool to better equip engineers when making appropriate design decisions. It is important to mention that simulation, to a great degree, has been misrepresented in the past. It does not completely replace the need for the physical prototype. Its role is to investigate behavior of design decisions and to remove the common cascade of errors to the prototype that force the multiple iterative stages between prototyping and manufacturing. The simulation concept is meant to shave away time in the design cycle associated with error-related prototype iterations. Improving Simulation with Real Measurements Circuit simulation is increasingly used technique in design. However, simulation is fundamentally a mathematical model of device behavior and is inherently limited by that math. Prototype validation still uncovers flaws that were not seen in the mathematical models of simulation. Therefore, the ultimate limitation for circuit simulation depends on how comprehensive the models are. Models for transistors, switched-mode power supplies and MOSFETs are complex and sophisticated and emulate circuit behavior quite accurately within defined regions of operation. In fact, SPICE models have been noted to sometimes better realize NOVEMBER 2008 printEd CirCuit dESign & fAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - November 2008

Printed Circuit Design & Fab - November 2008 Contents Our Line Market Watch Around the World Happenings ROI Positive Plating Ten Tips to Improve Manufacturability 3D Chip-Package-Board Modeling Improving Circuit Simulation With The Addition Of Real Measurements Ad Index PCB West: Interview with NBS Design Inc. The Influence of Final Finish on Lead-Free Assembly Reliability The Lead-free Soldering Challenges for Peelable Resists Off the Shelf Marketplace BGA Bulletin

Printed Circuit Design & Fab - November 2008

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