Designing a transistor amplifier to work at RF or microwave frequencies requires that its input and output impedance’s are matched at the desired frequency. Using Gapher these impedance’s are matched using either lumped or micro-strip lines. It is then up to the designer to add the biasing network for the transistor.
Designing a 6GHz Maximum Available Gain (MAG) amplifier by conjugate matching the input and output of the device.
The RF matching section of the amplifier is designed in Gapher.
Using the Amplifier window and entering the scattering parameters, Gapher calculates the conjugate impedance’s, MAG, Rollet Stability, Input Stability and Output Stability Circles with the Amplifier window.
Select the device and enter the substrate parameters to calculate the width of the micro-strip lines. The length of the lines will be determined during the matching procedure.
Match the conjugate input impedance using a micro strip line by selecting it. A micro-strip line is then joined to it. Selecting the micro-strip line in component sweep mode and running a simulation produces a graph. Drag the mouse across the Plot window until the cursor reaches the 1 radius in the Admittance chart.
Similarly using a micro-strip line stub to finish the input matching network, drag the mouse until the cursor is at 0 Ohms reactance on the Admittance chart.
Match the output impedance in a similar way using another micro-strip line.
And a micro-strip line stub.
The final circuit with the device in place for the microwave lines. All that is left is to add the DC biasing components of the device on the board to complete then circuit.