Qucs A Tutorial

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This chapter will describe an RF design issue using QUCS The author assume. that the basic manipulation of qucs is known You will find herein mainly a Ma. cOsX description that is close to a linux or unices architecture. choice of transistor, The choice has been made to choose among the Philips RF wideband transistor. library These components are easy to find with resonnable prices. This list could be found at http www semiconductors philips com. A resume of these transistors can be found in the figure 1. I will not discuss herein the reason 1 why of the final choice but the BF G425w. is the candidate It offers high gain with low figure noise if LNA consideration. high transistion frequency 25 GHz its emitter is thermal lead low feedback. capacitance This device could be used in RF front end analog or digital cellular. radar detectors pagers SATV oscillators It is in a SOT343R package suitable. for small integration, The maximum acheivable gain is 20 dB with 25 mA Vce 2 V at 2 GHz and. 25 C The third order intercept point in these conditions is typically 22dBm. These parameter should be compatible with our need Here are the spice parameter. of the device,SUBCKT BFG425W 1 2 3,L1 2 5 1 1E 09,L2 1 4 1 1E 09. L3 3 6 0 25E 09,Ccb 4 5 2 0E 15,Cbe 5 6 80 0E 15,Cce 4 6 80 0E 15. Cbpb 5 7 1 45E 13,Cbpc 4 8 1 45E 13,Rsb1 6 7 25,Rsb2 6 8 19.
Q1 4 5 6 6 NPN,MODEL NPN NPN,IS 4 717E 17 BF 145 NF 0 9934. regarding current Ft Vce power dissipation etc, Figure 1 transistor table 2from philips semiconductor. VAF 31 12 IKF 0 304 ISE 3 002E 13,NE 3 BR 11 37 NR 0 985. VAR 1 874 IKR 0 121 ISC 4 848E 16,NC 1 546 RB 14 41 IRB 0. RBM 6 175 RE 0 1779 RC 1 780,CJE 3 109E 13 VJE 0 9 MJE 0 3456.
CJC 1 377E 13 VJC 0 5569 MJC 0 2079,CJS 6 675E 13 VJS 0 4183 MJS 0 2391. XCJC 0 5 TR 0 0 TF 4 122E 12,XTF 68 2 VTF 2 004 ITF 1 525. PTF 0 FC 0 5501 EG 1 11,XTI 3 XTB 1 5, Since the model used in SPICE and in QUCS rely on a gummel poon modelisation. and since the level of modelisation is the same some quite direct conversion could. be used to create the library for QUCS, To use directly this file you will need to store the file in an other directory from. the project one a small bug taken into account Then it should work but some. there are still some issues on the parameters itselves This is the reason why we. will proceed in an other way, The data sheet could be found on the philips web site.
Figure 2 spice parameter extract,4 from philips data sheet. library creation, Remember that when creating a device it is almost always mandatory to read of. have a look at on how the model is done is the technical documentation It is very. to understand the limitation and how we can correct some data if needed The. mian pity is that a lot of commercial software are quite obscure on the real model. they use and their limitation QUCS is quite exceptionnal on this point this the. complete modeling is explain theoretically in a special technical paper. In order to conduct these test we need to create a model of our component To. perform this you should create the file that contain all the libraries this file is. stored under, usr local share qucs library philips RF widebande npn lib. You can edit this file with vi You need to add the following line. Qucs Library 0 0 7 philips RF wideBand,Component BFG425W. Description,RF wideband NPN 25GHz,2V 25mA 20dB 2000MHz.
Manufacturer Philips Inc,NPN complement BFG425W,based on spice parameter from philips. sept 2005 thierry,Description,BJT T BFG425W 1 480 280 8 26 0 0 npn 1 47 17e 10. 1 1 1 1 1 0 304 1 0 121 1 31 12 1 1 874 0,300 2e 15 1 3 1 484 8e 10 1 1 546 1 145 1 11 37. 1 6 175 1 0 1 1 78 1 0177 9e 3 1 014 41 1 310 9e 15. 1 0 900 1 0 346 1 137 7e 15 1 0 5569 1 0 207 1 0 500. 1 667 5e 15 1 0 4183 1 0 239 1 0 550 1 4 122e 12 1. 68 2 1 2 004 1 1 525 1 0 0 1 26 85 1 0 0 0 1 0 0,1 0 0 0 0 0 1 0 0 1 0 0 0 0 0. You can replace the 1 by 0 this will remove the visible checkbox the fact to place. a 1 first enable the user to change and or view the parameters that are being used. A trick to provide all the required syntax is to fill a NPN into the schematics. perform a copy on the device you should then have the model in the clipboard. just paste into to file and add the description and the markup language boundaries. The syntaxe is explained in the help at the topic description of the qucs file formats. Then the device is visible in the Component Library Tool as mentionned in figure. Figure 3 QUCS Component Library showing the new component. By doing this you haved the possibility to reuse the device as much as you want. and you can debug devices in a more easy way, Warning in this section we have only describe the die of the device for the.
parasitic from the package we will be obliged to describe this circuit but later on. device library verification, The first step before using the device in a application is to verify the model you. use Especially since this model has been created by the user In order to proceed. you need to rely on exact data that is to say the official datasheet. it this step you will need to create a project especially for the device verification. It is good to keep a trace of the device verification since you could have different. use of this device so it is good to be able to redo some simulation around the. model itself,The created project should look that the figure 4. project name model verif bfg425w,project location HOME qucs. For the validation we will need to use a specific bias of the device Ic should be. 25mA therefore Ib should be 300 A,Figure 4 QUCS project for model verification. Figure 5 DC validation and temperature,parasitic description of the package.
In order to simulate properly the device you need to used the correct package. that is to say the SOT 343R in our case as mentionned on the philips web site. Eventhough the device has two emitter the model used has only one emitter The. parasitic of this model are shoyn in the spice netlist described in the choice of the. transistor and reproduced in a schematic see fig 8 These parameter are always. critical to extract either you have the knowledge to do it or then you should rely. on the piece of information given by the device manucfacturer It is also very. difficult to figure out what have to be changed in such description of the device. Some fitting have been performed using 3D electromagnetic software in the time. domain based on MOM methods to verify these parameters. PhilipsO fifth generation double poly silicon wideband technology uses a steep. emitter doped profile resulting in transition frequencies over 20 GHz and with. poly base contacts a low base resistance is obtained Via the buried layer the. collector contact is brought out at the top of the die The substrate is connected. directly to the emitter package lead resulting in improved thermal performance. From this schematics you can edit the symbol that could be used in the next. simulation file To proceed type F 3 or edit circuit symbol from the file menu. Simply drw a npn transistor and come back to the schematic by re pressing F 3. Figure 6 SOT 343R package description, Figure 7 die connection if the fifth generation transistor from philips. Figure 8 bf g425W in sot343R package description,small signal S parameter verification. In this section we will need to redraw a new schematics using the model we have. created plus some extra components to place the measurements ports 2. You should have a schematics like the one mentionned in fig9. Figure 9 schematics used for S parameters simulation. The components used to verify the model could be strange inductor of 1H and. capacitor of 1F It is normal since we need to have a very wide band response on. the circuit and since we want to caracterize only the active device and compare. with the datasheet An other way is to use DC bloc or DC feed or bias Tee to. provide the power supply to the component This is the right way to do it. you should then create a display to visualize the S parameters generally s11 and. s22 are in the smith and s12 and s21 are in polar, We have now to compare these results with the measured parameters from philips. Filename 225bfg425 001,BFG425W Field C1, V1 8 667E 001V V2 2 000E 000V I1 3 585E 004A I2 2 496E 002A. S11 S21 S12 S22,Freq GHz Mag Ang Mag Ang Mag Ang Mag Ang.
We will another method when we will use the device in a real project. warning This chapter will describe an RF design issue using QUCS The author assume that the basic manipulation of qucs is known You will nd herein mainly a Ma

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