5/23 Op Amp Relaxation Oscillator

Today, we continued on the AC circuit analysis with op amp.
First, we did a example of the circuit with op amp with AC voltage supply. (I did not take a picture.)
An oscillator is a circuit that produces an ac waveform as output when powered by a dc input. Oscillator is a device which transform DC signal to AC signal. Without the existence of oscillator, AC signal will not exist.

In order for sine wave oscillators to sustain oscillations, they must meet the Barkhausen criteria:

1. The overall gain of the oscillator must be unity or greater. Therefore, losses must be compensated for by an amplifying device.

2. The overall phase shift (from input to output and back to the input) must be zero.

(From Day 23 AC Op Amps , Oscillators, AC Power.pdf)

Then, we did lab.

Op Amp Relaxation Oscillator

Pre-lab

We were planning to create a signal with the frequency 254 Hz (which is the last 3 digits of my student id). We need to have R=18k to produce this frequency.

The picture above is the basic set up for this lab. We used one 12k ohms resistor and two 3k ohms resistors to produce 18k ohms resistance.

Using Everycircuit, we have successfully proven that the circuit will provide an oscillating signal.

The picture is the result of our lab. Our measured value of frequency in our oscillator is 1/0.003740 = 267.3Hz. Comparing to the theoretical, we had a good result with a small percentage error:  5.23%.

Summary

We learned what op amp can do in a AC circuit, and how to use a op amp to produce oscillation. By doing the lab, we successfully implement what we learned before the lab, and we got a small percentage error of frequency from what we wanted to get (254Hz).