Device-modification (adding feedback and/or loading sections to a transistor in order to pre-condition it before the matching networks are synthesized) is usually the most important step in the design of an amplifier stage. Extensive modification capabilities are provided in the Device-Modification Module. Transistors can be stabilized easily, gain slopes can be modified or leveled, and the VSWRs can be improved before (lossless) matching. Transistors can also be modified to reduce the difference between an optimum noise match and an optimum gain match on the input side and/or to reduce the difference between an optimum gain match and an optimum power match on the output side.

Modification can be done with current-series feedback, voltage-shunt feedback and/or shunt or series loading. Tables of possible components which will result in a specified slope in the MAG or MSG can be created. More than one section can be used to modify the gain-slope of a transistor, if necessary (As an example, the first section can be used to remove half of the slope in the MSG, and the next to level the slope in the MAG). When different sections are combined to modify a transistor, the optimum slope to be removed by each must be determined iteratively.

The gain-slope modification techniques can also be used to stabilize a transistor. Tables of the resistance required to stabilize the transistor with any of the different modification sections can also be created. If possible, the values of the components required to provide the stabilizing resistance at the passband edges are listed.

A second technique, which automatically combines two modification sections of different types or two sections of the same type but on different sides of the transistor, is also implemented. When the double-section modification capability is used, a systematic search is done for the components that will level or slope the overall transducer power gain (G_T) | the available power gain (G_a ) | the available power gain associated with the optimum noise figure of the modified transistor (G_anopt) | the operating power gain (G_w) | the MAG or the MSG of the amplifier synthesized up to that point (with the gain of the stage designed included). The input or the output VSWRs for the stage designed are controlled directly at the same time. The capability to control the maximum unclipped output power too is also available as an option.

When the double-section modification capability is used, the required gain slope, the  range of acceptable gain values, the weight factors, the breakpoints and the zero-error points for the VSWRs, the noise figure and the degree of difficulty of the noise matching problem, the passband over which the gain must be leveled, the VSWR circles of interest, and the angular step to be used on these and the relevant constant gain circles must be specified. Solutions are then synthesized at a single frequency and a selection is then made based on the error function defined.

The Rollette stability factor can also be included in the double-section modification error function. The stability over the complete range for which parameters were specified or limited to the passband of interest can be considered.

The search can be done for a specific double-section modification topology, or a global search can be done. When a global search is done, the option to not use voltage-shunt feedback combinations is also provided. This is often useful when a packaged transistor is used. When the double-section modification section is entered with some modification sections already in place, the list of modification topologies is reduced automatically (Any specific modification section can only be used once).

If the operating (available) power gain of an amplifier is controlled, no lossless gain control network is required at the output (input) of the stage being designed. If the MAG is controlled, matching networks will be required at the input and the output sides. If the transducer power gain is controlled, no lossless matching networks are required (It is often possible to eliminate the need for any lossless matching networks in an amplifier totally at the lower frequencies). If the available power gain associated with an optimum noise match is controlled, matching networks are required on both sides of the transistor.

The connecting lines and/or pads required for the transistor and the lumped components can be specified before a modification network is synthesized in all cases. These lines are specified by specifying the equivalent characteristic impedances and electrical line lengths. If the microstrip option is used, the actual dimensions can be specified and the equivalent electrical parameters will be calculated and used. The connecting lines and pads specified are displayed graphically for verification purposes. This feature is also useful as an aid to decide whether the lines/pads specified are long enough.

Bond wire inductance can be specified for any resistors or capacitors used. The capacitor type (chip capacitors and single-layer parallel plate capacitors) and gap size can also be specified. Thin-film resistors can also be used in the device-modification section.

The option to use one or two resistors in any voltage-shunt feedback loop is also provided. If a single resistor is used, it can be positioned at the input or the output side of the feedback loop.

Simple parasitics can also be specified for the lumped components. These parasitics are taken into account when a double-section modification network is synthesized, but not when the gain-slope is modified with a single-section modification technique.

General optimization capabilities were added in the device-modification module. The error function used is the same as that used in the double-section modification section. If required, variables can be fixed or constrained during the optimization.

The maximum unclipped output power can now also be calculated and optimized in the device-modification section (This capability is provided as part of the Device-Modification and Circle Module Power Option; These capabilities are essential for the design of high dynamic range amplifiers). The maximum output power associated with the transducer power gain (modified transistor directly terminated in the stage terminations), the operating power gain (stage load termination used), the available power gain (source termination for the stage and a conjugate match at the output), the MAG (conjugate match on both sides), the optimum noise match and a conjugate match at the output, as well as the optimum power match can now also be calculated for the modified transistor.

A worst-case tolerance analysis can be done on the passive components of the modification network used (connecting lines excluded). The analysis is done for the design value, a lower and an upper value of each parameter of interest. The worst-case variations in the different parameters of interest are displayed in tabular form. When only one parameter is varied, the performances associated with the three different values of the parameter specified are compared (also graphically), and a worst-case tolerance analysis is not done.

A MultiMatch circuit file can be created for the modified transistor. This is useful if a feedback amplifier without a lossless matching networks is synthesized and also to verify that the lines used are long enough (artwork considerations). This feature can also be used to store different modification networks for later use.

Apart from any circuit files created for the different modification networks, the last modification network designed is stored for future use when the Device-Modification Module is closed. The option to import the stored modification circuit is provided when the connecting lines option is chosen in the main device-modification menu. Any circuit files created previously in the Device-Modification Module can also be imported at this point.