Our final example will show you how to perform transistor or FET parameter conversions using the X1G and X2G codes. These type conversions are very useful.

Most device vendors only give you scattering parameter data in one form, because its easier for them. But, suppose you're designing an oscillator, and want to investigate scenarios other than common emitter or common source? To do this, you need to convert the parameter set.

Once you do the conversion, and have s-parameter data in CB or CG form, you could use the Sceptre tweak feature to maximize the input port reflection coefficient in an effort to obtain a negative resistance.

To try this, choose "(1) Sceptre" from the Main Menu. either by pressing "1" or by using the "F1" function key, you'll enter the Sceptre Module.

            Sceptre Module

            Filename [<Enter>=Quit]  ? _

Enter "CECB" to call up the common emitter .CKT file, and then press <Enter>. Here is the file listing for a device at 2000 MHz::

TWO	AA	S1	50
X1G	BB	AA
PRI	BB	S1	50
END
2000
0.643	172.3	3.645	65.1	0.084	38.2	0.213	-91.3

              
The CE s-data given in the last line of the file is for a bipolar transistor operating at 2000 MHz. The X1G code in line 2, (where "X" is shorthand for "Xchange"), simply means to interchange port 1 and "ground." Since, in a CE or CG device, port 1 is the base/gate and "ground" is the emitter/source, the swap creates a CB connection.

As usual, after entering the filename up above, Sceptre asks:

            Analysis or Tweak (A/T) [<Enter>=Quit]  ? _

In response, type "A," and then press the <Enter> key to use the analysis mode.

Note: At this point, you'll be asked "Print Logfile (Y/N) [<Enter>=No] ? _" Please press <Enter>.

If you choose the option to 'Print Logfile,' the data will be directed to 'Logfile.txt' within the \mwdata2 sub-directory, and to the screen. Right-click on 'Logfile.txt' to print it, and then DELETE the file; it will re-create when next needed.

Please please <Enter> to choose "N" in response to the above question.

Sceptre will perform the parameter conversion and display the following results on-screen:


Sceptre Circuit Analysis on 07-18-2006 at 10:06:46

Filename:   CECB

Freq	S11 Mag/Ang	S21 Mag/Ang	S12 Mag/Ang	S22 Mag/Ang	S21(dB)  K  B1
2000	1.042/  167.0	2.129/  -34.2	0.122/  148.4	1.212/ -32.3	6.56  -0.98  -.43

Task Completed

Hopefully, by now, you'll have no problem in returning to the Sceptre Module entry point?


Concluding Remarks

These five detailed examples should give you a good feeling about Sceptre and how to use this powerful tool.

With this tool, you can accurately model a wide variety of circuits. We've used it to model three and four port networks, like power dividers, power combiners, etc. The secret is to be creative in your use of the various interconnection schemes offered, and to use low and high value resistors, like .01 ohm and 1 megohm, to simulate both shorts and opens. This tool opens up a whole new world, doesn't it?