IHP-AnalogAcademy/modules/module_2_50GHz_MPA/part_2_matching_ideal

Input Matching for the MPA

In this section, we will focus on matching the input and output of the MPA (Monolithic Power Amplifier) for a 50-ohm termination. For now, we will use ideal components to estimate starting values, which will later be refined through electromagnetic (EM) simulations. The goal at this stage is to explore the possible design space, not to finalize the design.

Step 1: Input Reflection Coefficient (S11)

The first task is to analyze the input reflection coefficient (S11) to ensure proper impedance matching. Starting from the schematic we developed in the biasing stage, we will run the simulation to observe the behavior of S11.

To visualize this, we begin by inspecting the Smith chart at 50 GHz, where we observe the initial impedance characteristics. The Smith chart provides a clear picture of how well the input is matched to the 50-ohm termination.

From this point, you can use a Smith chart tool of your choice to facilitate the matching process. In this case, we will perform an L-section matching, using a capacitor as the series element. For this, we utilized the following online Smith chart tool: Will Kelsey’s Smith Chart Tool

Step 2: L-Section Matching

After using the Smith chart tool, we determined that an inductor of 105 pH and a capacitor of approximately 45 fF provide a good starting point for matching the input. These values were chosen based on the Smith chart's behavior at the given frequency.

With the estimated component values in hand, we return to the schematic and insert the components accordingly. This results in the updated schematic, where the inductor and capacitor are now part of the matching network.

Step 3: Fine-Tuning the Parameters

Once the components are added to the schematic, we can use the Smith chart again to visualize the S11 reflection coefficient. Fine-tuning the values of the input inductor (Lin) and capacitor (Cin) is an iterative process, and after optimization, the following values were obtained:

• Lin \approx 96 pH
• Cin = 45 fF

These values help to achieve a better match, improving the impedance at the input. (Remember this can vary from you design)

For the output we leave it as is, since we will match the output for maximum linearity.