Overview The preparatory work for designing a single-stage power amplifier with a Mitsubishi MGF0909A will be done in this example. The main steps in this initial phase are to 1.Open a new circuit file with the required substrate, terminations and passband specification. 2.Fit a small-signal model to the S-parameters of the MGF0909A transistor. The dc operating point and the four boundary lines defining the allowable load-line area on the dc I/V-plane must also be specified when the model is fitted. The model and the load-line constraints are used to find the optimum load-line for maximum output power, as well as analysis of the power performance. 3.The transistor and the lines defining the connections to be made to the transistor will be added to the circuit file. Note that the drain and gate flanges of the transistor also behave like transmission-lines and that these lines do not launch immediately onto the microstrip substrate. The substrate for these sections is actually air (er=1). The substrate height is also different from that of the microstrip substrate (a recess is required in the box to mount the power transistor).
Open a new circuit
Select the document type
Select the substrate type
Specify the terminations to be used
Specify the number of passbands
Specify the analysis frequency range and the passband
Specify the microstrip substrate
A name must be specified for the new circuit
The name specified for the circuit
The startup schematic of the new circuit
Select the FET Model Command from the Analysis Menu
The dialog for opening the S-parameter data file of the transistor to be used is presented
The mgf0909a.s2p data file is selected
An Amplifer Design Wizard (ADW) label must be specified for the set of S-parameters
Choose the Initialize Command to fit a basic model to the specified set of S-parameters
The Error Type, Target Parameters, Weight Factors and Frequency Range specified
The frequency range over which the parameters must be fitted initially
The Error Type, Target Parameters, Weight Factors and Frequency Range specified
The S-parameters of the model (single color traces) are compared with the specified parameters (mixed color traces)
Bounds are set before optimizing the component values
The trans-conductance is constrained as shown
Rds is constrained too
The constraints set for Rg
The constraints set for Rd
The constraints set for Rs
Lumped package components can be added on this page
A small value was specified for each of the elements
The optimization option was set for each of the components
Select the Optimization Command on the Intrinsic Model Page
The frequency range is set to the full range
The Least-Square Error and the Y-parameters are selected again
The fit after optimization
Zooming in to view the fit in s21 more closely
Selecting the L1 error and the S-parameters to be used in the next optimization cycle
The fit obtained
Viewing the fit in s11 and s22 more closely
The fit in s21 and s12
The intrinsic elements fitted
The package elements fitted
The I/V Curve Boundaries Page
The boundary lines and the operating point specified
A rendering of the specifications
Select the OK Command on the Intrinsic Model Page to save the model fitted
The Twoport Command is selected to insert the transistor into the circuit
The transistor will be inserted between the two lines
The insert position is marked with the vertical line shown
The name of the S-parameter data file is specified
The next page of the Twoport Wizard
The page for specifying the artwork vectors and the transistor configuration
The specifications made for the MGF0909A
A rendering of the artwork vector specified
The twoport has been inserted into the schematic
The command to insert a microstrip line into the schematic is selected
The line will be inserted to the right of the input line
The position of interest is marked with the vertical line
The dimensions of the line and the substrate to be used are specified
The line inserted
A line will be inserted to the right of the transistor next
The position of interest is marked in the circuit file
The parameters of microstrip line to be inserted
The electrical parameters of the inserted line
The artwork will be displayed next
The artwork of the circuit
The line editing command will be selected next
The line editing dialog box
The input line was selected for editing
The line length is set at 2mm
The shortened input line
The output line will be shortened too
The line length is again set at 2mm
The shortened output line
Preparing to insert a line
Saving the artwork changes made
A line will be inserted between the two lines on the input side
The new line
A second new line was inserted into the schematic
Two new lines were inserted on the output side too
The modified schematic is saved
The artwork will be edited again
The width of the selected line will be reduced
The artwork edited to prepare for the matching networks to be synthesized
Matching networks will be designed in the next example to maximize the output power and the match the input of the transistor. Leveling the gain instead of matching the input will also be considered. Next Phase of the Design