The application consists of the following elements:
This view provides a field for the retrieval of an existing transistor device file or for the input of a new device file. After a file name is entered "return" brings up the INPUT VIEW. For convenience the files may be logged in the provided text view.
All of the required input data are entered in the appropriate text fields. The data consists of:
Provision is made for S parameter values at center frequency, low band edge, and high band edge. If the design assumes constant S parameters over the band simply enter the center frequency values only and with zero values entered for the other fields. The values are entered in pairs of magnitude and angle and where the angle value is in degrees.
If the design will not include noise parameters and or microstrip realization, the same method of zeroing out the appropriate fields is used.
The required microstrip parameters are: characteristic impedance, Z0; substrate relative dielectric constant, eps; substrate height (thickness); input and output stubs termination, open or short. The microstrip dimensions units can be inches or centimeters and are set by a switch in the info panel which is accessed by the " info" button. The units in use are shown in the "Subs Height" label.
This view presents stability information and a range of Available Gain and Noise Figure circles on the Smith Chart Source Plane and Operating Gain circles on the Load Plane. The information presented is used to assist in the design process. The first decision point is whether to affect a Source Plane design or a Load Plane design. If design is with respect to an input noise figure, then a Source Plane design is dictated. Another consideration might be if there is a need for a good input (output) match then a Load (Source) Plane design is indicated. For a Source Plane design, several Available Gain/Noise figure circles are plotted. For the Load Plane case several Operating Gain circles are plotted as well. This overview can be helpful in choosing a gain/noise figure tradeoff and/or load/source impedance optimization. Note that the gain dots represent maximum gain (available or operating) while the noise figure dot represents minimum noise figure. Pressing the "Source Plane" or "Load Plane" button opens:
Initially shows small filled circles (dots) which correspond to the maximum Available Gain and minimum Noise Figure for the Source Plane case and the maximum Operating Gain for the Load Plane Case. For the Source Plane case consistent values of gain and noise figure are entered. If the values chosen are consistent (as indicated in the overview) there will be two intersection points or a tangent point. A touch at the chosen point will bring up the normalized impedance and corresponding reflection coefficient. The Load Plane will be for a specified Operating Gain only. A point selected anywhere on a constant gain circle or constant noise figure circle results in a design realizing that value. Additional considerations in the choice of an operating point on a given circle are proximity to stability circles and the effect on overall circuit "Q". Pressing the "Match Networks" button opens:
Here is presented the microstrip parameters and dimensions for a mircrostrip realization and the corresponding values for a lumped element realization. The frequency sweep is entered in the Start and Stop fields. It should be consistent with the s parameter data originally entered. The number pad is dismissed by the "return" button and pressing the "MS Response" or the "LE Response" button for the desired response brings up:
The design essentials are conveniently summarized on this single view and includes:
A touch on the gain response plot will show the corresponding gain and frequency values. The response for a different frequency sweep is accomplished by a return to the "MATCH NETWORKS AND FREQUENCY SWEEP VIEW". The response plots provide a valuable feature of the app. The effect on circuit Q and resulting bandwidth is a function of the choice of operating point and microstrip stub termination. These effects may be readily observed and ameliorated by iterating the design for different operating points on the Source/Load Plane views and for the two terminations. Additionally it is noted that the intrinsic circuit "Q" is much lower for the lumped element realization. This is a consequence of the fact that the microstrip lines present exact reactance only at the design center frequency due to the transcendental nature of the "equivalent" elements.
The response plots reflect idealized performance as a consequence of several factors as follows:
Marcus Staloff
© 2013