# Microelectronics Assignment 5

Your report should be a Microsoft Word document or PDF. You must submit your JELIB files and SPICE schematics and other associated files.

#### Exercises

1. Use Electric to create a layout of the inverter you designed in exercise 5 of assignment 4. It would be easiest, I think, to modify tutorial 3 for this purpose. Determine the parasitics for this layout, and incorporate them into your LTSpice design from assignment 4. Show a netlist of the new LTSpice schematic.

2. Using the geometry of the layout above, derive by hand from its geometry the parasitics (AD, AS, PD, PS) and compare to the Electric netlist.

3. Use SPICE to generate the DC transfer curve of the above inverter. Show the test schematic used to generate this curve. Use the inverter symbol generated from the previous assignment. Then locate the switch point and transistion points and generate a bar chart showing the noise margins. Locate these points on the a drawing of the transfer curve.

4. Use SPICE to find the linear dependence of the rise and fall times vs load capacitance for your inverter. You should include a plot of the data points you generated, a schematic of the circuit used to generate the data, and the equations of the fitted lines for high-to-low and low-to-high transitions.

5. Substitute another inverter for the load capacitance in the previous problem, calculate (using SPICE) the rise and fall times for the first inverter, and use the results of the previous problem to determine the input capacitance of the second inverter. Compare the result to the combined gate capacitance of the two transistors in the inverter.

Note. In the above two questions, you can use either rise/tall times (2.2 τ) or propagation delay (0.69 τ) and solve for R and Cout from the linear fit.

6. Generate a three-inverter chain driven by a pulse voltage source. Find the average propagation delay as a function of the inverter number. Calculate the equivalent rise and fall time for the pulse source to most closely represent the inverter waveform. Generate a diagram in which you shift the time of the waveforms to allign them to the pulse source. The midpoint voltages (VDD/2) should all correspond and the rise and fall time of the pulse source should approximate the rise and fall of the inverter signals. Document the schematic of the circuit used in this analysis.

7. Generate a 15-inverter ring and show a few periods of oscillation. Show your schematic. Does it matter where you place the voltage probe? Find the period (and frequency) of oscillation. Compare to the calculation of frequency based on propagation time. Hint: You may need to place an initial voltage condition on one of the inverters to get the system to oscillate.

8. Work through tutorial 4 (see link below). Your report should include layout figures, schematic figures, and other analysis and diagrams discussed in the tutorial.

Tutorial 4 – Design, layout, and simulation of a CMOS NAND gate – electric_tutorial_4_video.wmv (42:25)

Maintained by John Loomis, last updated 24 February 2014