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Multisim/Ultiboard for Low-Frequency Simulation and Layout

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by AWR Corporation

Introduction

RF and  microwave circuit designers choose Microwave Office® software because of its complete range  of powerful circuit design capabilities, from  design capture, to harmonic balance and  time-domain simulation, to layout, synthesis, and  optimization, and  even  electromagnetic (EM)  analysis and  post-layout verification.

The  Microwave Office  design environment is well  suited for higher-frequency designs, and, when  combined with  National Instrument’s Multisim circuit simulation software through AWR  Connected™, low-frequency circuit functionalities are added for an even  more  complete circuit design flow  (DC  up through microwave/RF). Moreover, NI’s  Ultiboard printed circuit board  (PCB)  layout  software is capable of integrating high-frequency circuit layouts with  Multisim, enabling designers to rapidly create a layout  of a complete prototype, add  mechanical and  graphical shapes to the  design, create 3D views  of the  final  design, and  export standard Gerber files, as well  as other  formats, for fabrication.

With  the  flexible routing capabilities of Ultiboard, all the  particular details of the  RF circuit affecting the  frequency response are preserved (such  as the  transmission line  bends, matching networks, and  ground vias), while  all the  complementary low-frequency circuits are quickly routed around it.

Microwave Office
The AWR Design Environment: Microwave Office 10 GHz LNA example project.

Getting Started in Microwave Office

In the  AWR  Design Environment™, go to File>Open  Example and  select  the LNA_10GHz.emp project. This  project shows the  design of a 10GHz low  noise amplifier (LNA) built  on 10-mil alumina using  an NEC  76038 gallium arsenide (GaAs) metal  semiconductor field  effect  transistor (MESFET). Run  the  analysis and  it can  be seen  that  the  LNA  has  7.7dB gain  and  2.15dB NF at 10GHz.

Designing this  amplifier in Microwave Office  enables users  to take  advantage of the  software’s real-time tuning and  frequency subset Smith  Chart  plots, as well  as AWR’s proprietary X-models to account for discontinuities, so that  performance can be optimized and  validated before committing to fabrication.

Next, let’s  take  DC biasing into  consideration and  turn  to NI’s  Multisim/Ultiboard software.

Create a Multisim Component for the LNA

DXF Export

To create a biasing circuit in Multisim, export the  relevant DXF  file from  the Microwave Office  environment by going  to Layout>Export  and  saving the  design file as a DXF  file on your  computer. Remember that  the  project units  were  in mils.

Now, go to Ultiboard and  open  a blank  design. Go to Tools>Database>Database Manager and  click  on Create a New Part, then  select  New PCB  Footprint in the pop-up dialog  box.

Figure 1 shows the DXF  import dialog. In your  new  footprint design file, go to File>Import>DXF and  import the DXF  file that  you exported from  the Microwave Office software. Make  sure  you only  import the copper layer  (merge it with  the copper top layer)  and  ignore the rest  of the layers. Remember to set the units  to mils.

Select the  imported shapes and  right-click to go to their  properties. Under the copper area  tab, make  sure  you  change the  fill style  to a solid  fill style.

Preview of the LNA layout
Figure 1: Preview of the LNA layout in the Ultiboard DXF import dialog.

Adding Pins

You  now  need  to create 10 pins  to connect the  LNA  to its DC circuitry: one  pin each for RF input, RF output, drain  bias, and  gate  bias  and  six ground pins  that  connect the through vias  to the  ground. To add  the  pins, go to Place>Pins. The  LNA  layout after  adding the  vias, copper fill, and  ports  in Ultiboard is shown in Figure 2.

Adding the LNA to the Ultiboard Database

Once  you have  finished editing the layout, go to File> Save to Database as and  save  the new  component to the user  database. The  final  layout  of the LNA  component should look  similar to that shown in Figure 3.

LNA layout
Figure 2: LNA layout after adding proper ground vias, copper fill, and ports in Ultiboard.
Ultiboard database
Figure 3: Save the LNA component into the Ultiboard database for reuse

This  LNA  design can  now  be used  in Ultiboard, where DC biasing and  other  low-frequency circuitry can  be built  around it. At this stage, where distributed high-frequency effects no longer need to be considered in the  PCB  layout, designers benefit from  the easy-to-use PCB  prototyping capabilities of Ultiboard.

Conclusion

NI Multisim/Ultiboard and  AWR  Microwave Office  software are complementary and together offer  capabilities that  enable designers to create circuits spanning from DC to microwave frequencies. Complex tasks  such  as harmonic balance simulation and  SPICE  analysis can  now  be accomplished with  a high  degree of accuracy, and  RF layouts can  be readily combined with  rapid  prototyping tools  inclusive of both  low  and high-frequency circuitry.

To evaluate NI Multisim circuit simulation and  Ultiboard PCB  layout  software, visit www.ni.com/multisim/try

AWR  would  like to thank  Mahmoud Wahby for his contributions to this application note.

Mahmoud Wahby, M.Sc Product Marketing Engineer National Instruments Toronto www.ni.com.

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