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SCAT V2.0 Scattering Parameters Program (C) 1991,92 by J.Herron CONTENTS 1. Introduction.....................2 2. Installation.....................2 3. How To Use Help..................2 4. Menus Explained..................3 5. Functions Available..............3 6. File Operations..................3 7. Unilateral Analysis..............5 8. Bilateral Analysis...............6 9. Noise Analysis...................9 10. Matching........................9 11. Using The Chart................10 12. Options Menu...................11 13. Example1.......................12 14. Example2.......................12 15. Example3.......................13 16. Registration...................14 17. References.....................14 James Herron Aciran Software Systems, 29 Duncryne Place, BishopBriggs, Glasgow G64 2DP Scotland. Page - 1 Introduction. This program computes a number of useful S-Parameter functions and makes use of a Smith Chart to display the results. After starting the program and observing the copyright notice the user is presented with the main screen which is divided into three sections. At the top is the menu selection which allows access to the various functions performed by SCAT. At the left of the screen is the information window which is where SCAT outputs information about the Device that is being analysed. The area between the menu and information window is the chart where most results and input forms appear. Installation. SCAT can be run from a single floppy disk drive, however use off a hard disk is recommened as the floppy disk will fill up as you create more and more data files. First of all make working copies of you Master disks and then put them in a safe place, use DISKCOPY as instructed in you Dos handbook. To install on a hard disk first create a directory by typing md SCAT <return>, cd SCAT <return>. Place you Master disk in drive A and from the SCAT directory on your hard drive type copy a:*:* <return>. The main files are: SCAT2.DOC This file SCAT2.COM Loads Graphics driver then main program. SCAT2.EXE The main program. SCAT2.HLP Help File for On Line context sensitive help. SCAT2.CFG Configuration file, will be created if not present. ORDER.FRM Registration order form, Please Use it. EGAVGA.COM Graphics driver for EGA & VGA adapters. EGACHART.PCT The Smith Chart. SCAT forces EGA mode as this is easier to read. PRINTER.COM Generic Printer Driver (default is HP LaserJet II). Registered disks have the following additional files. EPSON.COM Printer driver for Epson compatible printers. IBMPRO.COM Printer driver for IBM Proprinter compatible printers. HPLASER.COM Printer driver for HP LaserJet II compatible printers. There may be a number of example data files on the disk, but these are not essential to the operation of the program. These have extension *.SPD. Scat has a comprehensive on-line help facility, it can be accessed at any time by pressing the F1 key. A help box will open on the screen at a page relevent to where you are in the program. How to use Help You can move around in help by pressing the PgUp or PgDn keys to move one page at a time, or you can use a mouse and select the direction to move in by pointing to the scroll bar at the side of the help window and clicking the left mouse button. Exit Help by pressing the Esc key or use the mouse to click on the cancel button. Page - 2 A number of option buttons appear at the bottom of the help box. You can select a button by using the mouse or cursor keys. For example if you select index you will see an alphabetic list of subject headings along with page numbers. If you point to the heading and click the left mouse button you will jump to that page. To use the keyboard press tab to enter the window and use the cursor keys to scroll up and down to reach your choice, then press enter and you will jump to that page. The Menu System How to use the menus When Scat starts you will be presented with a menu which has a number of choices. File Unilateral Bilateral Noise Matching Chart Options The sign on screen displays a copyright notice and after a few seconds the Smith chart is loaded and displayed. There are two ways in which you can select a menu option, depending on whether or not you have a mouse fitted. The Use of the KeyBoard and Mouse Keyboard Only If you only have a keyboard then you enter the menu by pressing the F10 key. This will pull down the first menu option, and you use the cursor keys to move around the different selections available. Once you have highlighted your choice simply press return to select it. Certain menu choices may not be available depending on the type of device being used, and on the data present, eg S-Parameters and/or Noise data. Mouse Option If you have a mouse simply point to the menu and click the left mouse button to open it. Next point to the selection of your choice within the menu and click the left button again. The Menus Explained What the menu options mean File This menu presents the following options. System Reset New Scattering Parameters Edit Scattering Parameters Load a File Save a File Quit to Dos Each will be briefly explained. For Detailed information please consult the printed manual. Page - 3 System Reset Choose this option to reset the system to its initial start-up state. You will be warned that all data will be lost. You should select this option if you wish to start work on a new device which has only Noise or Scattering parameter data, but not both, otherwise you may find you have inherited some Noise or Scattering parameters from any previous device in memory. New Scattering Parameters Select this option to enter New Scattering Parameter Data. A fill-in form will appear and you should enter the information requested. The Zo field is already filled in with the current Zo value. You can move through each field in turn, or jump around, perhaps to correct an error,by using the cursor keys or mouse to select any field. Click on the continue button when complete, or select the cancel button or press Escape to abort. All scattering parameter magnitudes must be greater than zero, all angles must lie between -360 and +360 degrees. Any attempt to violate these input conditions will result in an error message, and the form will re-appear for correction. You may abort input at any time up to the last entry by simply pressing Esc. Enter all the S-parameters including a device ID and the frequency at which measurements were made. This last information is not used in any calculations, it is purely for reference and is shown on Graphs to help you identify which device was used. The device ID would normally be the component type, eg BFP96. Edit Scattering Parameters This option is similar to the New Parameters option except the form contains the current data values for editing purposes. You can select any fields you want to change (except Zo), and once satisfied select the continue button to change the data, or press the cancel button or Escape key to abort. Load a File This allows you to retrieve previously saved data by selecting the appropriate File. When this option is selected a Load Box will pop up on the screen and you will be prompted to select the data file to be loaded. Use the mouse or cursor and return keys to move through the folders to reach the file you want to use, the Tab key will give access to the three buttons which allow you to change drive,enter a folder, or cancel the operation. When selected the Load Box will close and the file will be read by the computer. Most operations cannot be performed until either the S-parameters or noise data have been entered or loaded, and this brings us to the next menu option. The component data file may contain either S-parameter data or noise data or both. The operations allowed will depend on what information is available. There is no reason why you could not enter only Noise data and perform noise analysis if that is all you required, S-parameters data can be added later if desired. Page - 4 Save a File This allows you to save newly entered data by entering a File name. When this option is selected a Save Box will pop up on the screen and you will be prompted for a Dos file name. If the data was loaded previously from a file, that name will appear in the save box and you may accept it or change it to another. Use the mouse or cursor and return keys to move through the folders to reach the directory you want to use, the Tab key will give access to the three buttons which allow you to change drive,enter a folder, or cancel the operation. When selected the Save Box will close and the file will be written to disk by the computer. Quit to Dos As the name suggests this option allows you to exit the program and return to DOS. If you have changed your data you will be asked if you wish to save it. You also will be asked to confirm exit to Dos. Unilateral Menu This menu has the following options. Gain analysis Plot Gain Circles Each will be described briefly, see printed manual for more details. Gain Analysis This options performs a Unilateral analysis on the device. This option will display a table of Unilateral parameters including the Stability factor K, the unilateral figure of merit U, and the min and max gains available for the device connected to Zo source and load impedances, and the additional gain contributions possible for conjugate matching of the source and load. Refer to the manual for a fuller explaination. The following equations are used:- U = |S11 S12 S21 S22 | |(1-|S11|^2) (1-|S22|^2)| Gu = |S21|^2 |(1-|S11|^2)(1-|S22|^2) Gmin = 1 Gmax = 1 (1+U)^2 (1-U)^2 Go = |S21|^2 = transducer gain for Zo input and output impedance. Gu = Go * G1 * G2 G1max = 1 G2max = 1 1-|S11|^2 1-|S22|^2 Page - 5 [Unilateral Analysis] U = 0.09 Gu = 6.02dB Ga min = 5.25dB Ga Max = 6.86dB Go = 2.28dB G1 max = 3.17dB G2 max = 0.57dB Fig 1. Press the continue button to remove the table, or press the Print It button to obtain a printed report. Plot Gain Circles Use this option to construct input and output gain circles for a Unilateral amplifier design. The circles can be used for an inheritly stable device which is being treated as Unilateral. A form will appear requesting gain contributions required from the source and load. The max values availble are shown in brackets. The constant gain circles for source and load will be drawn on the chart. The output circle is drawn thicker to distinquish it from the input circle on mono monitors and when copied to the printer. The following equations are used:- roi = Gi Sii poi = sqrt(1-Gi*(1-|S11|^2)) 1+Gi|Sii|^2 1 + Gi *|Sii|^2 center of circle radius of circle Bilateral This menu has the following options. Simultaneous Conjugate Match Bilateral Stability Circles Plot Bilateral Gain Circles Each will be described briefly, see printed manual for more details. Simultaneous Conjugate Match If the device in memory has a stability factor K greater than unity it is inherently stabily and can be conjugately matched for maximum gain without worry of instability due to input or output loads placed on the device. Choose this option to get the source and load impedances and reflection coefficients for conjugate matching, and the value of maximum available gain. If the device is unstable it will not be possible to select this menu option. When the results are presented you may print a Report by clicking on the Print button, ensure the printer is ready. Page - 6 The following equations are used:- K = 1+|D|^2 - |S11|^2 - |S22|^2 2|S21*S12| where D = (S11*S22-S21*S12) Gmax = | S21 * (K+/- sqrt(K^2 - 1)) | | S12 | the plus sign is used when B1 is negative and the negative sign is used when B1 is positive, where B1 = 1 + |S11|^2 - |S22|^2 - |D|^2 The optimum source and load impedances are calculated from Tms = C1* * |B1 +/- sqrt(B1^2-4|C1|^2)| | 2*|C1|^2 TmL = C2* * |B2 +/- sqrt(B2^2 -4|C2|^2)| | 2*|C2|^2 where C1 = S11 - D * S22* and C2 = S22 - D & S11* C1* = complex conjugate of C1, C2* = complex conjugate of C2. B1 = 1 + |S11|^2 - |S22|^2 - |D|^2 B2 = 1 + |S22|^2 - |S11|^2 - |D|^2 Bilateral Stability Circles If a device is unstable use this option to plot the input and output stability circles. The output circle is drawn thicker to differentiate it from the input circle. Refer to the manual to determine whether the inside or outside of the stability circle is the stable region. This option will plot Bilateral stability circles on the Smith Chart. The output stability circle is plotted thicker than the input circle to distinguish them on a mono screen or printer. The following equations are used:- rsi = | Ci* | psi = | S21 * S12 | | |Sii| - |D|^2 | | |Sii|^2 - |D|^2 | rs1 = location of center of stability circle on I/P plane rs2 = location of center of stability circle on O/P plane ps1 = location of radius of stability circle on I/P plane ps2 = location of radius of stability circle on O/P plane These circles indicate the boundary between stable and unstable regions, they do not indicated which is which. The area either inside or outside the circle will represent a stable operating condition. Page - 7 To determine which area represents this stable operating condition, let's make ZL = 50 ohms, or TL = 0. This represents the point at the center of the Smith chart. Under these conditions |Ts| = |S11|. Let's now assume that S11 is less than one, Ts is also less than one, this means that the point TL = 0 represents a stable region. If we select another value of TL that falls inside the stability circle we would have a potentially unstable situation. If on the other hand |S11| > 1 with ZL = 50, then this area would be the stable region. Caution: S-Parameters are typically measured at some particular frequency. The Stability circles are draw for that frequency. We cannot be sure that the device will be stable at other frequencies unless you check them out. Plot Bilateral Gain Circles Use this option to plot constant gain circles for a Bilateral amplifier design. If the device is stable the input form requests the gain required and shows the maximum available in brackets. For unstable devices the maximum gain in indeterminant, however gain circles can still be plotted, and a warning given if the value entered cannot be achieved. See the manual for more details including worked examples. This option is for Bilateral gain circles. The gain required is input in dB and load gain circles are plotted on the Smith Chart. The following equations are used:- ro2 = | G | * C2* | 1+D2*G | center of circle po2 = |sqrt((1-2K|S12*S21|*G+|S12*S21|*2*G^2))| | 1 + D2 * G | radius of circle where G = Gp/Go Gp = desired gain, and Go = |S21|^2 the transducer gain D2 = |S22|^2 - |D|^2 New Noise Data Select this option to enter Noise data. A form will appear and you should fill in the necessary information. Note that the noise resistance is in ohms and NOT normalised as in some manufacturers data sheets. Fmin is the min noise figure for the device (at the frequency stated) and is in dB and must be greater than zero. Edit Noise Data Use this option to edit noise data previously entered. The data will be verified to be consistent with practical devices, eg Fmin must be greater than zero. Page - 8 Plot Noise Circles You will be asked to enter the noise figure to plot. This must be greater than or equal to Fmin, if not an error message will be given and the form will reappear for correction. The data required is Rn (ohms), Fmin (dB), Optimum noise source (magnitude and angle). Finally enter the noise figure to be plotted. The following equations are used:- Center of circle = CFI = To 1 + Ni and radius = sqrt(Ni^2 + Ni*(1-|To|^2)) 1 + Ni where To = optimum Noise source reflection coefficient fo Fmin Ni = Fi - Fmin where Fi = Noise Figure Requested 4*rn rn = Rn = Normalised equivalent Zo noise resistance. Be careful when using manufacuters data sheets as some give Rn (ohms) and others rn (normalised to Zo). Source Match for Given Load Use this option to calculate the conjugate Source matching impedance (reflection) for the device, when connected to a given Load. You will be presented with a choice of entering Impedance or Reflection coefficients. Tick the box for the type of input you want to use. If you select impedance you will be asked for the load impedance in terms of a real and imaginary impedance. If you selected Reflection you will be asked for the magnitude and phase of the reflection. You will then be presented with the value of source impedance and its corresponding reflection coefficient, and the values of maximum transducer gain GT and max operating gain GP. When the results are presented you may print a Report by clicking on the Print button, or Plot the source impedance by clicking Plot. This option calculates the optimum source impedance given the desired Load impedance placed on the device output. The following equations are used:- RmL = | Sii - RmL*D |* where RmL = Load impedance in the | 1 - RmL*S22 | form (X + jY) ohms Load Match for Given Source Use this option to calculate the conjugate Load matching impedance (reflection) for the device, when connected to a given Source. You will be presented with a choice of entering Impedance or Reflection coefficients. Tick the box for the type of input you want to use. If you select impedance you will be asked for the source impedance in terms of a real and imaginary impedance. If you selected Reflection you will be asked for the magnitude and phase of the reflection. You will then be presented with the value of load impedance and its corresponding reflection coefficient, and the values of maximum transducer gain GT and max operating gain GP. Page - 9 When the results are presented you may print a Report by clicking on the Print button, or Plot the load impedance by clicking Plot. This option calculates the Load impedance for optimum matching, given the source impedance placed on the input of the device. The equation used is TmL = | S22 - RmS * D | where RmS = Source impedance in the | 1 - RmS * S11 | form (X + jY) ohms Chart Menu The Chart Menu has the following options: Plot Impedance Read Impedance Clear Chart Print Chart Select Zo Each will be described briefly, see printed manual for more details. Plot Impedance Use this option to plot an impedance (reflection) on the Smith Chart. You may do this to ensure that a chosen source or load does not lie in an unstable region. See the examples in the manual. You will be presented with a choice of entering Impedance or Reflection coefficients. Tick the box for the type of input you want to use. If you select impedance you will be asked for the impedance in terms of a real and imaginary impedance. If you selected Reflection you will be asked for the magnitude and phase of the reflection. The impedance (reflection) will then be plotted on the smith chart as a small circle. Read Impedance This option allows you to read impedance or reflection directly from the chart. You cannot use this option unless you have a mouse. Brief instructions are given. When inside the Smith chart click on the left mouse key to read the chart. The corresponding value of impedance and reflecion are displayed at the bottom of the information window. You can read the chart continuously by holding down the left button or pressing any key (eg. space bar) while moving the mouse pointer. If you move off the chart, or press the right mouse button, the reading operation will terminate. You can also stop by pressing the Escape key. Useful if you selected this option by mistake and do not have a mouse present. Using right button copies data to input forms. Clear Chart Quite simply this will clear the chart by reloading it from disk. You will be given a warning before proceeding. If you want to keep the chart, perhaps to superimpose different sets of results, you may cancel by pressing Escape or clicking on the cancel button. Page - 10 Print Chart This option will dump the chart onto a printer. You will be given the opertunity to abort if you wish. The printer should be on-line and have paper. Scat uses the currently selected printer driver. Select Zo The default value for Zo is 50 ohms. Use the option to select one of the common values of 50,75,100,300,or 600 ohms by checking against it's box. Alternatively you can choose Other, and a form will appear asking for the value of Zo you desire. Zo must be greater than Zero. Options Menu The Options Menu has the following options: Select Printer Date Format Set Hot Keys Each will be described briefly, see printed manual for more details. Select Printer Scat supports three printer drivers, these are Epson or compatible IBM proprinter HP LaserJet II or compatible You will be presented with a list of these options and you should select one. The current driver will be highlighted. This information is stored in a configuration file along with the Date format and the list of user defined Hot keys. See pages #32 and #33. Date Format When printing Reports Scat Time Stamps them with Date and Time information. In the UK the date format is normally DD/MM/YYYY and in the USA it is MM/DD/YYYY. This option allows you to select the format for you country. This information is stored in a config file and so need only be set up once. Set Up Hot Keys Experienced user may prefer to bypass some or all the menus by assigning Hot Keys to the menu items. Some have already been set, eg control [L] to load a file. You can set your own control keys using this option. Try to choose letters that mean something so that you will remeber them. this info is stored in the config file. This option gives a list of choices. You can program each menu item, Clear a menu item, Clear alll items, or cancel out without changing anything. If you decide to set up a hot key, you will be asked to select the menu item. Use the mouse to highlight the menu choice and click the left button. A dialog box will ask you for the letter to use along with the control key. When you exit Scat this info is saved for future sessions. Page - 11 Examples. Three example transistor data files are supplied. These are BFP96, HXTR3121, and HXTR6106. The BFP96 is unconditionally stable at the frequency of interest, the HXTR3121 is conditionally stable, and the HXTR6105 contains only Noise data. Example 1: HXTR6105. This transistor is the subject of a Hewlett Packard application note number AP17, Noise parameters and Noise Circles. Application notes are usually free on request from HP. The example covers the transistor at 2GHz, and the following noise data should be entered when New Noise Data is selected: Rn = 5.04 Fmin = 2.25 |To| = 0.429 <To = 173 Zo = 50 If you do not wish to enter the parameters select Load from the File menu and enter HXTR6105 in response to the filename. The current value of Zo is saved and loaded as part of the data file. Select Plot Noise Circles and enter a noise figure of 3.0 The Noise circle will be drawn on the Smith Chart, and a hard copy may be obtained by pressing Alt-P when the chart is displayed. A copy of the result can be seen in Graph 1, this is from an EGA display adapter. Example 2: HXTR3121. This example is also based on an HP application note number AP998, A 75 ohm 470 - 806 Mhz Low noise Amplifier. The transistor parameters a 470 Mhz are: S11 = 0.72 < -156.0 S12 = 0.04 < 31.9 S21 = 9.16 < 95.9 S22 = 0.35 < -62.0 Zo = 75 Frequency = 475 Mhz. Either enter or load the parameters. This device is potentially unstable, so plot the Stability Circles for this frequency. The thick circle represents the output stability circle, the thin one the input. Select Bilateral Gain and enter a value of 19. The output Bilateral Gain circle for 19dB will also be drawn on the chart alongside the stability circles, see Graph 2. Any point chosen as a load on this circle will give 19 dB gain. Select a point away from the unstable region, (50 - j54 in this example). Select Load/Source Matching and enter the value of Load chosen. The corresponding input match for maximum gain is given.in terms of impedance and Reflection. Page - 12 Example 3: BFP96. Enter or load the following S - Paramerters for the BFP96 S11 = 0.72 < 152.0 S12 = 0.12 < 52.0 S21 = 1.30 < 42.8 S22 = 0.35 < -87.0 Zo = 50 Frequency = 2GHz Select Unilateral Gain, the results are shown in Fig 1. The device is stable at this frequency. Choosing Bilateral Gain will give the K stability factor, the Maximum gain, and the conjugate input and output match required to obtain this gain. Select Unilateral Circles. Enter Gain values for GS and GL equal to 3.0 and 0.5 respectively. Observe the gain circles as depicted in Graph 3. The center of these circles is where G1 and G2 max are found. Select Unilateral circles again and enter values of 1.0 and 0.2 for GS and GL. Observe the new circles added to the chart. These circles along with say noise data enable the designer to achieve the best trade off between gain and noise figure, while keeping a watchful eye on stability. Graph 1. See Manual for Details. Graph 2 See Manual for Details. Graph 3 See Manual for Details. Page - 13 Why Register Scat is distributed using the Shareware principle of Try before you buy. This is NOT a FREE program by shareware. If you use Scat you are expected to register with the author. It is only through your support that shareware can bring you Quality Software at affordable prices. By supporting the Author you encourage him to spend more time providing the extra features that YOU want to see. If you have any comments or would like extra functions added then feel free to write to me about them. Registration brings the following benefits: 1. A disk containing the latest version of the program. 2. Free Technical telephone support for 6 months, and free upgrades in that time period. 3. A printed bound manual produced on a Laser printer using Ventura DTP containing many more examples than in this abridged version. 4. Additional printer drivers for Epson & IBM Proprinter printers. References. All the calculations in Scat have been tested using many worked examples from authoritive texts on the subject of Scattering Parameter Analysis. Some of the works referenced are: High Frequency Amplifiers By Ralph S. Carson. Transistor Designers Guide By Microwave Associates Ltd. S-Parameter Design, HP Application note 154 S-Parameter Techniques for Faster, More accurate Network design, HP Application note 95-1 A 75 Ohm 470-806 Mhz Low Noise Amplifier Using the HXTR-3121 Bipolar Transistor. HP Application note 998. Noise Parameters and Noise Circles for the HXTR-6101,-6102, -6104, and -6105 Low Noise transistors. HP Application Bulletin 17. RF Circuit Design by Chris Bowick Page - 14