CMOS Inverter & Ring Oscillator Theory: In this Lab we will implement a CMOS inverter and then use it as a building block for a Ring Oscillator. MOSfets (Metal Oxide Semiconductor Field Effect Transistors) will be used for both circuit topologies. Inverter: The inverter is universally accepted as the most basic logic gate doing a Boolean operation on a single input variable. Figure 1 depicts the general structure of a CMOS inverter. As shown, the simple structure consists of a combination of a pmos transistor at the top and an nmos transistor at the bottom. Figure 1 Cmos Inverter 1 of 5
Ring Oscillator: A ring oscillator is a device composed of an odd number of NOT gates in a ring, whose output oscillates between two voltage levels, representing true and false. The NOT gates, or inverters, are attached in a chain and the output of the last inverter is fed back into the first, as presented in Figure 2. Figure 2 Generic Ring Oscillator Figure 3 Ring Oscillator Figure 4 Modified Ring Oscillator 2 of 5
Software Aided Simulations using ADS: Inverter: 1. Build the schematic presented in Figure 1. 2. Depending on the input voltage which transistor is ON at any given moment? Justify. 3. Run a transient simulation and present the input and output waveforms. 4. Calculate the voltage gain (Av). Ring Oscillator 1. Build the schematic presented in Figure 3. 2. Present plots for the output signal. 3. Calculate the Oscillation Frequency of this waveform oscillator. 4. Increase the supply voltage. What happens to the oscillation frequency? 5. Modify your circuit to the one presented in Figure 4. 6. Run a transient simulation and present the output signal. 7. Find the new oscillation Frequency. 8. Modify the resistor values. What happens to the oscillation frequency? 9. Compare the results of these two topologies. What effect does the addition of the resistors impose in both frequency and output signal integrity? Justify. 3 of 5
Lab Experiment: Inverter 1. Construct the circuit presented in Figure 1. 2. Connect a sinusoidal input signal 0-6V with a frequency of 100Hz. 3. Connect CH1 and CH2 of the oscilloscope and present the input and output waveforms. 4. Calibrate the input signal in order to have an output signal ranging from 0-4V. 5. What is the small signal gain of the inverter? Ring Oscillator 1. Build the circuit presented in Figure 3. 2. Present plots for the output signal. 3. Measure the Oscillation Frequency of this oscillator. Does it differ from the one you calculated during the simulation part of this experiment? Justify. 4. Increase the supply voltage. What happens to the oscillation frequency? 5. Using the math function of the Oscilloscope present the first harmonic frequencies and comment on both their amplitude and their corresponding frequency. 6. Modify your circuit to the one presented in Figure 4. 7. Present plots for the output signal. 8. Measure the new oscillation Frequency. Does this frequency agree with the one provided by the simulations? 9. Modify the resistor values. Do your frequency measurements agree with the simulated ones? 10. Using the math function of the Oscilloscope present the first harmonic frequencies and comment on both their amplitude and their corresponding frequency. 11. In both topologies what is responsible for the initiation of the oscillation? Justify. 4 of 5
The connection diagram of your CD4007 IC is as follows. Figure 5 Good Luck! 5 of 5