In the following, you will investigate the response of circuits using capacitors and inductors when they are excited by

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In The Following You Will Investigate The Response Of Circuits Using Capacitors And Inductors When They Are Excited By 1 (135.91 KiB) Viewed 13 times

In the following, you will investigate the response of circuits using capacitors and inductors when they are excited by step changes in voltage. In particular you will look at the simplest switching circuit where a MOSFET transistor is used as a voltage controlled switch. The digital circuit you will look at is often called an inverter or sometimes a level-shifter. The idea of the circuit in Figure 1 is that when the input is at a Vi VDD M R Vo Vi VDD SR model for PET Ron Figure 1. Inverter circuit with MOSFET M Figure 2. Inverter with MOSFET SR model. low voltage the output is at a high voltage, VDD, and when the input is at a high voltage the output drops to near zero volts. For purposes of this assignment, the MOSFET can be modeled as a switch in series with a resistance, Ron (see Figure 2.) The switch is controlled by V₁. When Vi is low, the switch is off and, since there is no current in R, V. = VDD. When V₁ is high, the switch is on, and a voltage divider is formed with VDD. In the ideal case Ron would be zero, and V. would equal zero. If Ron has a more practical value, but still relatively small, V. will be close to zero; we will be working with this case where Ron has a relatively small, nonzero value. In the following you will look at different choices for the resistance R in Figure 1 with the goal being a level shifter that will convert an input pulse going from zero to
5V to an inverted output pulse going between 3V and a low voltage, less than 0.25V. In the following, assume VDD = 3V and Ron = 280 ohms. Inverter Static Response. Problem 1) When the input is low, the circuit uses zero power from the power supply VDD. Convince yourself of this. When the input is high, the switch closes, and current flows. Find an expression for the power used in that case written in terms of the variables VDD, Ron, R. If the circuit must use less than 1mW of power when the input is high, what is the smallest R could be? Find the output voltage when you use this minimum resistance. Simulate the circuit on CircuitLab (use the MOSFET component instead of an Ron resistor). Use a square wave input varying between 0V and 5V with a 50% duty cycle and a 100uS period. See Appendix I for details on the simulation, including MOSFET parameters. Check that your output goes between 3V and the low voltage you calculated. Compare the low simulated voltage to what you calculated and