Lab #4: Op Amp Circuits EEGR 317, Spring 2018

Read all instruction very carefully before starting the lab. Use Op Amp 741 to complete circuits and spice model. Warnings: make sure that the ground of the oscilloscope and power supply are the same.

Part 1: Clipping During Amplification Op-amps cannot provide infinite output voltage and have saturation voltages equal to the positive and negative DC bias on the om amp, ±15V. At the saturation voltages, the op-amp will begin “clipping”. In periodic waveforms, clipping appears as a “flattening out” of the output voltage at the peaks of input wave.

A) Evaluate the circuit to determine the voltage gain. At what input voltage would you expect to start seeing clipping of the output voltage? Explain your reasoning. B) Use spice to simulate the expected voltage gain. Does SPICE simulate the clipping effect from op amps? Take screenshots of your spice model and output data. C) Construct the inverting amplifier circuit. Make sure to set the frequency using the function generator and measure using the oscilloscope. Apply bias to the circuit, display vin on CH1 and vout on CH2. Starting with a 2V peak-to-peak sine voltage waveform, gradually increase the amplitude of the input signal and record the input amplitude when the output starts clipping. Is this what you expected? D) With the input set at the amplitude that is producing clipping, slowly lower the supply voltage of the op-amp from its initial value of ±15V. What happens to the output’s clipping? Can you explain this? Make sure you take photos of the circuit and input/output wave forms.

Part 2: Voltage Division Compare the voltage and current response at the load of a simple voltage divider and a voltage divider with a unity buffer circuit.

A) Calculate Vout as a function of the load Resistor, RL, for both circuits. B) Construct the both voltage divider circuits. Record Vout as a function of, RL, varied between 500Ω and 10kΩ for both circuits. Make sure you take photos of the circuit and input/output wave forms. C) Record Iin as a function of, RL, varied between 500Ω and 10kΩ for both circuits (take at least 10 data points). D) Describe some differences and advantages of using one type of voltage divider vs the other.

Part 3: The Integrator and Differentiator In addition to the sine wave and the square wave, there are two other common signals in electronic instruments, the triangle and sawtooth voltage waveforms. Both waveforms consist of voltages that change in time. These waveforms can be manipulated by using special integrator and differentiator circuits. For the following circuits assume R = 1kΩ and C = 0.1uF, bias using ±12V.

A) Evaluate both circuits to determine the voltage output, show work. Draw what you expect to see at the output if the input waveform is a square wave, sine wave, and triangle wave. Explain your reasoning. B) Use spice to simulate the expected voltage output for an input waveform with a square wave, sine wave, and triangle wave, assuming an input voltage frequency of 1kHz. Take screenshots of your spice model and output data. Does the response for both circuits behave as expected? C) Construct both circuits. Make sure to set the waveform and frequency using the function generator and measure using the oscilloscope. Apply bias to the circuit, display vin on CH1 and vout on CH2. Starting with a 2V peak-to-peak input amplitude, use an input waveform with a square wave, sine wave, and triangle wave, assuming an input voltage frequency of 1kHz. Use photos to record the circuit, and input/output wave forms for each waveform on each circuit. Does the output voltage behave as expected? In addition to a change in shape is their any amplification or phase shifts that occur? D) Repeat part C, with an input voltage frequency of 10Hz, 100Hz, 1kHz, 10kHz, and 100kHz. Do you notice anything different about the output voltage waveform, amplitude, or phase as the frequency increases?