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