Day 21 - Oscillator

Topics Discussed

On day 21 of the ENGR 44 course, we were introduced to op-amps that were integrated into AC circuits. We used impedance instead of resistance to find the gains in each circuit, but we utilized the same equations previously discussed for op-amps. We did a few practice problems that utilized the same methods as previously, only working now in the complex domain and using impedance. (Fig. 1)

Fig. 1

We were also introduced to oscillators, which essentially create an ac waveform in its output when supplied by a dc source. 

Op-Amp Relaxation Oscillator

Today in lab, we planned to investigate an op-amp oscillator, which would utilize a dc input and output an ac waveform. In order to do this, the Barkhausen criteria have to be met. That is, the overall gain of the oscillator must be unity or greater, therefore stating that losses must be compensated for by an amplifying device. Additionally, the overall phase shift from input to output must be zero.

Once we understood the workings of the oscillator, we proceeded to make the circuit according to the lab manual specifications. (Fig. 2)

Fig. 2

We then measured the output signal to see if we had an ac waveform. (Fig. 3) This wave showed that we were able to successfully create an op-amp oscillator.

Fig. 3

Summary

Today, we were able to successfully create an oscillator using an operational amplifier. Putting in a dc circuit, we were able to generate a waveform in the output. This alternating voltage came about due to the charging and discharging of the capacitor in the circuit, which essentially allowed the voltage to fluctuate and thus create the ac signal that we were reading.