RF Analog Digital WP1

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TECHNICAL PUBLICATION

Designing RF, Analog and Digital on PCB

A Unified Systems ApproachJohn Isaac, Director, Marketing Development - Mentor Graphics

March 2008



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 pureRF, 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 mixedtechnologies together and resulted in

multiple databases representing the final

product.

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 logicaland 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, RFdesign 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

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-to-

market and quality of the products.

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.

Figure1 – Separate systems interfaced with cumbersome ASCII

files works but can cause loss of designer productivity and a

non-competitive product.

Previous Model for RF Design



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.

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.

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.



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. Itcombines the logic of the schematic, the shapes and a set of rules that govern the final configuration.

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.

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.

Figure 5 -- The “auto arrange” function follows connectivity from the schematic and implements a correct-by-

construction RF circuit.

Figure 6 – A real time interface from the PCB design tools to the RF

simulation tools improves the productivity of the designer.



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 analogor 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 7 – The ability to cross probes demonstrates the tight integration between the RF and

PCB design systems.

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.



PAGE 6

Corporate HeadquartersMentor Graphics Corporation8005 S.W. Boeckman RoadWilsonville, Oregon 97070 USAPhone: 503-685-7000

Pacific Rim HeadquartersMentor Graphics (Taiwan)Room 1603, 16F,International Trade BuildingNo. 333, Section 1, Keelung RoadTaipei, Taiwan, ROCPhone: 886-2-27576020Fax: 886-2-27576027

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Silicon Valley HeadquartersMentor Graphics Corporation1001 Ridder Park DriveSan Jose, California 95131 USAPhone: 408-436-1500Fax: 408-436-1501

Japan HeadquartersMentor Graphics Japan Co., Ltd.Gotenyama Hills7-35, Kita-Shinagawa 4-chomeShinagawa-Ku, Tokyo 140JapanPhone: 81-3-5488-3030Fax: 81-3-5488-3031

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 thisinformation. Mentor Graphics is a registered trademark of Mentor Graphics Corporation. All other trademarks are the property of their respective owners.

For more information, call us or visit: www.mentor.com/pcb

03_08 LVG TECH7920-w.

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.

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.

Figure 9 – Stitching shielding vias is now automated replacing a

time consuming operation.

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