Designing RF, Analog and Digital on PCB A Unified Systems Approach John Isaac, Director, Marketing Development - Mentor Graphics March 2008

Transcription

1 TECHNICAL PUBLICATION Designing RF, Analog and Digital on PCB A Unified Systems Approach John Isaac, Director, Marketing Development - Mentor Graphics March

2 INTRODUCTION The presence of Radio Frequency (RF) circuitry on PCBs is no longer just a mil/aero industry requirement. The explosion of the wireless handheld communications devices is driving the need for pure RF, and, mixed analog, digital and RF designs at a significantly increasing rate. Handhelds, base stations, computer wireless, and mil/aero systems now all contain RF. For years, the design of RF has been a special art, requiring specialized design and analysis tools, by highly specialized designers. Typically, the RF portion of a PCB was designed by that specialist in a completely separate environment and then merged into the rest of the mixed technology PCB. This process was highly in-efficient, often required iterations to marry the mixed technologies together and resulted in multiple databases representing the final product. design must be corrected in the standalone RF solution and re-translated into the host PCB. A total replacement versus an incremental change. An additional problem is that the simulation in the RF solution only simulates the RF circuitry an isolated circuit and not in the context of a real circuit board with traces, components, vias, ground fill, etc. These additional shapes can have significant effects on the RF circuitry operation. This old methodology has been used successfully for years to design mixed technology boards but as the RF content in products increases, the problems with having two separate design systems is starting to significantly impact designer productivity, time-tomarket and quality of the products. Previous Model for RF Design By working closely with the suppliers of RF design tools, Mentor Graphics has developed a new approach and an integrated solution that addresses these issues and results in significant improvements in designer productivity, design cycle time and product documentation. The integrated design solution enables the complete logical and physical design to be accomplished in one environment (tools and RF shape libraries) that is tightly integrated with state of the art RF simulation functionality. THE OLD WAY In the past, design functionality was performed (and repeated) in two separate design environments through ASCII interfaces. Both the PCB system design and the RF specialized design systems had their own libraries, RF design databases and design archiving. It required that design data (schematic and layout) and libraries be managed (and synchronized) in both environments through cumbersome ASCII interfaces. With this old methodology, the RF designer basically was developing the RF circuitry isolated from the rest of the PCB system design. The RF portion was then translated into the PCB design using ASCII files to create schematic and physical implementation on the host PCB. If problems exist with the RF circuitry, the Figure1 Separate systems interfaced with cumbersome ASCII files works but can cause loss of designer productivity and a non-competitive product. INTEGRATED APPROACH Now, Mentor and leading RF design tool suppliers have developed an integrated solution. The complete design schematic and layout are seamlessly integrated across the systems linked to the RF simulation using a dynamic link rather than ASCII interface. This provides for a synchronized library and an environment where design intent is preserved between RF and systems design. Now the RF designer can become an integrated member of the design team. A truly integrated design flow thus eliminating the time consuming and error prone steps with translations and synchronization.

3 As well the RF circuitry is developed in the context of the rest of the PCB. Changes are immediately reflected and can be analyzed in the RF design tool thus reducing design iterations. The result of this new methodology is significant increase in productivity, reduction in design cycle times and time-to-market, and dimprovement in product functionality and quality. New Model for RF Design Figure 2 Tightly integrating the PCB and specialized RF systems improves designer productivity. DESIGN TEAM COLLABORATION -- A REVOLUTIONARY APPROACH Not only have leading RF design tool suppliers and Mentor worked together to develop an integrated system, Mentor s patented Xtreme technology has been utilized to provide for simultaneous design and analysis by multiple designers on a common central database. This means that for large RF boards, multiple RF designers, at the same location or globally dispersed around the world and connected on the company s LAN or WAN network, can concurrently work on the same design thus significantly improving their design cycle times. As well, for mixed technology boards, the RF, digital and analog designers can work simultaneously instead of serially. Figure 3 - Xtreme technology enables multiple designers around the world to design the same PCB simultaneously.

4 DESIGN PROCESS -- DEVELOPING THE SCHEMATIC Using the common RF library, a designer can enter RF schematic in either the RF tool or the system design tool (Figure 4). The designer adds parameters to these generic schematic symbols setting up for the synthesis function that will generate the physical shapes. Figure 4 The schematic for the RF circuits can be entered in either Mentor's Expedition Enterprise or Board Station flows (DxDesigner, DA/BA), or, in leading RF speciality suppliers entry tools. SYNTHESIZING THE RF SHAPES Typically, the libraries contain generic RF shapes. The specific RF shapes for this design are automatically synthesized on the fly based on user entered parameters. The RF parameters can be specified on the schematic or entered on a pop-up menu. Once synthesized, the shapes can be can be modified in layout to adhere to placement and clearance constraints on the board. The simulation of the shapes may highlight needed modifications to perform the desired functionality.

5 CREATING A CIRCUIT FROM THE SCHEMATIC AND SHAPES With RF circuitry it is not good enough to just connect the components with random net lines. The component shapes must be directly connected (all shapes are functional including net lines) and configured to perform the correct RF function. An auto arranger (Figure 5) that automatically performs this task has been developed. It combines the logic of the schematic, the shapes and a set of rules that govern the final configuration. Figure 5 -- The auto arrange function follows connectivity from the schematic and implements a correct-byconstruction RF circuit. SIMULATING THE DESIGN Using a real time interface, the designer can simulate the circuit using specialized RF simulation tools. This includes simulation of the RF shapes, custom shapes, packaged parts, traces, plane shapes and thermal ties. Figure 6 A real time interface from the PCB design tools to the RF simulation tools improves the productivity of the designer. The link between the PCB design and RF design tools is real time which allows for cross probing between the systems. Shapes can be probed in the PCB environment and highlighted in the RF environment, and vise versa.

6 Figure 7 The ability to cross probes demonstrates the tight integration between the RF and PCB design systems. If the simulation of the shapes does not meet the desired functionality, the shapes can be changed either by adjusting the parameters (re-synthesis) or by manually editing the RF shapes or other components/shapes (custom shapes, packaged parts, traces, plane shapes and thermal ties) in either the PCB or RF layout environments. An easy to use function keeps the two environments synchronized. MANIPULATING GROUPS Placing the RF circuitry on the PCB and then being able to adjust its position relative to the rest of the analog or digital circuitry requires that the RF shapes be tightly locked in place relative to each other. Otherwise, a slight change in their relative position can drastically change their functionality. For this purpose, capabilities exist to hierarchically group the RF circuitry and then manipulate it as a group rather than individual shapes. Figure 8 Identifying and manipulating groups maintains the integrity of the RF circuitry. Also in conjunction with groups, a designer can specify clearances between a group and other shapes that might cause improper RF circuitry operation. This applies to both X-Y and relative Z axis clearances. The relative Z axis clearance to various objects allows for maximum control of RF design as they are re-arranged by the PCB designer on the same or different layers of the PCB.

7 AUTOMATING STITCH VIAS To properly interconnect ground planes or to shield RF shapes often requires the addition of several (could be hundreds) vias. If done manually, this could be a very long process. The PCB layout product provides the ability to specify a via pattern and then instantiate those vias automatically. This can occur in very specific patterns or to merely flood and area with vias. Figure 9 Stitching shielding vias is now automated replacing a time consuming operation. THE BOTTOM LINE The tight integration and powerful schematic and layout functionality of Mentor s PCB design flows combined with specialized RF design and simulation products, results in an opportunity for RF and mixed technology PCB designers to significantly increase their productivity, decrease design cycle time and time-to-market, and improve design quality. This new methodology represents a unique and positive step in the industry. For more information, call us or visit: Copyright 2008 Mentor Graphics Corporation. This document contains information that is proprietary to Mentor Graphics Corporation and may be duplicated in whole or in part by the original recipient for internal business purposed only, provided that this entire notice appears in all copies. In accepting this document, the recipient agrees to make every reasonable effort to prevent the unauthorized use of this information. Mentor Graphics is a registered trademark of Mentor Graphics Corporation. All other trademarks are the property of their respective owners. Corporate Headquarters Mentor Graphics Corporation 8005 S.W. Boeckman Road Wilsonville, Oregon USA Phone: Silicon Valley Headquarters Mentor Graphics Corporation 1001 Ridder Park Drive San Jose, California USA Phone: Fax: Europe Headquarters Mentor Graphics Corporation Deutschland GmbH Arnulfstrasse Munich Germany Phone: Fax: Pacific Rim Headquarters Mentor Graphics (Taiwan) Room 1603, 16F, International Trade Building No. 333, Section 1, Keelung Road Taipei, Taiwan, ROC Phone: Fax: Japan Headquarters Mentor Graphics Japan Co., Ltd. Gotenyama Hills 7-35, Kita-Shinagawa 4-chome Shinagawa-Ku, Tokyo 140 Japan Phone: Fax: _08 LVG TECH7920-w. PAGE 6