Procedure

This is the initial section of the procedure that guides you through the setup process for analyzing the CMOS inverter. First, you need to launch your chosen circuit simulation software, which is essential for creating and testing your inverter circuit. Then, create a new project to organize all your related files.

Next, the actual schematic entry is done by placing the essential components of the CMOS inverter, which include an nMOSFET and a pMOSFET. You also set specific W/L ratios, which dictate the operational characteristics of these transistors. Make sure you connect the components correctly: the gates must be tied to the input signal (Vin), and the drains provide the output (Vout). You should also ensure proper connection to the power supply (VDD) and ground (GND).

After setting up the schematic, you move on to configure a DC analysis. This part involves setting the voltage for the input (Vin) and establishing the specific parameters for the DC Sweep simulation to gather data over a range of voltage values. Run the simulation to generate the Voltage Transfer Characteristic (VTC) curve, which essential for understanding how your inverter performs.

Lastly, it involves recording the key parameters from the VTC, such as VOH, VOL, Vth, VIH, and VIL, as well as calculating noise margins to assess the robustness of your design.

In this section, we explore how modifying the Width-to-Length (W/L) ratio of the transistors impacts the inverter's performance. First, you will vary the nMOSFET’s width while keeping the pMOSFET's width constant. By reducing or increasing the nMOS's width, you can directly observe changes in the VTC, which reflects the inverter's ability to switch states. The two cases demonstrate how a weaker (lower width) nMOS affects the VTC compared to a stronger one. Each variation requires you to run the DC sweep again to see its effect on Vout across the input range.

Next, you will return to the original nMOS width and change the pMOSFET’s W/L instead. Keeping the nMOS constant allows you to isolate effects caused by changes in the pMOSFET. Similar to the nMOS testing, two cases (weaker and stronger) will allow you to observe how the VTC shifts based on the transistor performance.

Finally, the optional section encourages finding an optimal ratio between the pMOS to nMOS that results in a balanced performance, aiming to achieve specific voltage thresholds and noise margins that are crucial for reliable digital circuit design.

After conducting the experiments, the observation/analysis section encourages you to compile your results systematically. You will create tables to document the measurements obtained from the various configurations you tested, making it easier to visualize how changes in the W/L ratios impacted the inverter's performance. Additionally, taking screenshots of the VTC plots reinforces the results by providing a graphical perspective of your findings.

In the analysis step, you will reflect on your data, discussing how the inverter performed initially and whether your results met the expected ideal outcomes. You will analyze the effects of variations in W/L ratios on the VTC, explaining how the inverter's parameters changed with these adjustments and linking these changes to the underlying physical principles of MOSFET operation.

For robust digital design, the focus on achieving symmetry around Vth and balanced noise margins is critical. By reflecting on your results, you gain insights into how your design holds up against theoretical expectations, highlighting any non-ideal behaviors observed and their respective causes, such as resistance in the transistor outputs or body effects that might have resulted from the specific settings used during your simulations.