Dipl.-Ing A.Gerstlauer DG5SEB and Dipl.-Ing J.Gerstlauer DC9SX

PUFF 2.1 - Improved and Expanded Version

VHF Communications 2/1998

Puff has become widely accepted as standard high-frequency CAD software, even in Germany. For many high-frequency developers, it has become a firm fixture in the workshop as a bench tool to assist with development. The 2.1 version introduced here has some remarkable new functions.

1. GENERAL

Puff has become a standard software for the high-frequency CAD domain in recent years, with over 17,000 copies sold world-wide. The current 2.0 version has been on the market since 1991. It incorporated a series of new functions (as against the previous versions, 1.0 and 1.5) which grew out of practical applications.

Professor Dave Rutledge at Caltech Institute is currently working on a Japanese version. Then a new version is to be produced for use with Windows 95, which will also include the new features in the 2.1 version developed by ourselves and introduced here. In addition to the operator interface (Windows 95), further changes planned relate to expanded high-frequency functions and, above all, to the user manual, which at the moment has unfortunately become very confused.

The reason why Puff is so popular is undoubtedly because it is easy to use. The fact that all the input and output parameters can be simultaneously displayed on the screen, where they can easily be viewed, makes for very efficient operation. In contrast to many other high-frequency simulation programs, only a brief reactivation period is required, even if it has not been used for a long time. The models used (e.g. for the line configurations) are sufficiently precise for most applications. Provided the limitations of the program are adhered to, its use can go far beyond a mere hobby.

2. CHARACTERISATION OF PUFF 2.1

The Puff 2.1 version introduced here is based on the 2.0 version. Some very interesting additions have been made. In particular, there are these items above all:
The plot routine has been expanded by the addition of a "q" mode (for "quick"). In the quick mode, the computing result is made available only after the complete calculation has been finished. Since the screen display does not have to be altered after each item is calculated, the computing time is considerably shortened, as against the standard plot function.

The quick plot routine is called up, in an analogous way to the standard plot routine, by pressing the "q" key in the plot window (F2). The key combination, "Ctrl-q" works in the familiar way in quick mode too, first displaying the last simulation results computed, and then adding the newly calculated values as well. The functions "p", "q", "Ctrl-p" and "Ctrl-q" can be used in combination.

Probably the most interesting new feature has come out of practical experience. For the complex calculated reflection factors S11, S22, S33 and S44, the elements of the associated series or parallel alternate circuit can now be obtained!

To do this, after the carrying out of the "p" or "q" plot routine, the cursor is then positioned on the desired parameter Snn in the plot window. Activate the '=' key, and the Rs and Xs elements appear in the message box, together with the associated capacity or inductance value for the series alternate circuit. The Rp and Xp elements are correspondingly displayed, together with the associated C and L values of the parallel alternate circuit, if the Smith diagram has been converted from the impedance representation to the admittance display.

The standard 1 - 2 - 5 gradation has been incorporated into the Smith diagram to provide a more precise interpretation.

Another new factor is the incorporation of a series of additional device files. The complete range of 'dev' files available now comprises: a voltmeter (vm.dev), a voltage-controlled voltage source (vs.dev) with a 20mS steepness, a differential amplifier (da.dev) for amplification 1, and an operational amplifier (op.dev) with an open-circuit voltage amplification of 10000.

All symbols are now uniform in that they have the input on the broad side of the triangle symbol and the output on the pointed side.

All devices are once again described in detail in Table 1.

The program contains some errors which are expressed, for example, in arbitrary program crashes, linked to error messages of the type "Runtime error at...". A whole range of errors of this type has been eliminated.

In some computer installations, the cursor displayed defective behaviour, in that it flashed too frequently. This was combined with occasional "sticking" when the program started. This error has been corrected.

The defective hard copy routine (premature termination of printing, or incomplete print-outs with some printers) has been corrected through the patching of the external supplementary program 'VGA2LASR.COM'.

The system has been matched to various national keyboard layouts. It should now be possible to use version 2.1 for working with all the different keyboard layouts correctly (i.e., as described in the manual). In particular, the key combinations 'Shift-1' to 'Shift-4' were not being correctly handled in the board window (F4) on non-American keyboards.

3. INSTRUCTIONS FOR USE

To use Puff 2.1, call up 'puff'. In the 2.1 version, all the functions are accessible through the corresponding keys as described in the manual.

When using the device files in the low-frequency range, remember that the voltage amplification, Snm, will be displayed multiplied by a factor of 2, corresponding to 6 dB. In the low-frequency range, the reference value at the amplifier input is the generator open-circuit voltage. For the S-parameters, as is usual in high-frequency technology, our reference is the generator output voltage, which is 6 dB lower when match-terminated.

If the new model of differential or operational amplifier is being used in the low-frequency range, select a meaningful average frequency, fd, in the board window (F4).

The differential amplifier can be used for potential-free voltage measurement. If the voltage drop is measured at a (small) shunt resistance, the current can thus also be measured.

The impedance or admittance values of the calculated S11 to S44 values are printed out as described in Section 2. After the carrying out of the plot function (using 'p', 'q', 'Ctrl-p' or 'Ctrl-q'), the cursor is positioned on the desired value, Snn, in the plot window (F2). Activate the '=' key. The specification for the Rs and Xs elements belonging to the selected S-parameter for the equivalent alternate series circuit appears in the message window, and the C or L corresponding to the Xs at the operating frequency. Fig. 1 shows the print-out for a simple example.

The corresponding Rp and xp values, and the associated value for C or L for the equivalent alternate parallel circuit are outputted if the Smith diagram is converted (through the 'Tab' key) from the impedance representation to the admittance display. Fig. 2 shows the associated print-out for the example above.

4. PROTECTED MODE VERSION OF PUFF 2.1

In addition, an experimental protected mode version of Puff 2.1 has been filed in the 'PROT\' sub-directory. However, this is still at the Beta stage.

The protected mode version can be called up from the 'PROT\' sub-directory through 'puffp'. In contrast to the standard version, the protected mode version actuates the entire main memory of the computer, which means larger circuits can be processed or more items can be calculated for the analysis. The maximum permissible number of plot points has been increased to 1000.