Reference no: EM133720277
Project - Wien Sinusoidal Oscillator
Objective: This project will demonstrate the basic operation and design of a Wien bridge RC oscillator in Fig. 1.
Components: 741 op-amp, 1N4001 diodes
Introduction: An oscillator is a circuit that converts a dc input to an ac output. This project investigates sinusoidal, output oscillators. Sinusoidal oscillators consist of an amplifier in a positive feedback loop with a frequency selective network. The amplifier can be a transistor amplifier or an operational amplifier. The frequency of the oscillator is determined by the frequency selective network. The criteria for an oscillator to produce sinusoidal oscillations are that the magnitude of the loop gain equal unity and the phase of the loop gain equal zero at the frequency selected for oscillations.
An oscillator with a loop gain of exactly unity is unrealizable because of varying component values, parameters, and temperatures. To keep the oscillations from ceasing or increasing, a nonlinear circuit can be used to control the gain and force the loop gain to remain at unity. The Wien bridge oscillator of Figure 2 uses two diodes in the circuit to limit the amplitude of the oscillations.
The Wien bridge oscillator without amplitude stabilization is shown in Figure 1. Wien bridge oscillators are noted for high stability and low distortion. This oscillator will oscillate at the frequency fo=1/2πRC, when R2/R1≈2.
Detailed instructions for the project:
Design the Wien bridge oscillator shown in Figure 1 with an oscillation frequency in the range of 1.9 kHz and 2.1 kHz. Use ±15 V supplies for the op-amp.
Simulate your design with PSICE. Plot the output waveform, find fo.
Try different variables for Wien bridge oscillator circuit of Figure 1. For example, use the designed values vs. standard values for the resistors and capacitors. Capture the waveform output of the oscilloscope, include the plot in your report. Note any distortion in the output waveform or if oscillations begin to increase without bound. If oscillations do not start, try increasing the ratio R2/R1 to slightly greater than 2.0. This can be done easily if you use the decade resistance box for R2. If oscillations increase without bound, try getting the ratio R2/R1 closer to exactly 2.0
Determine the frequency of the oscillations. What is the peak amplitude of the oscillations? Measure the actual values used for R1 and R2. Now add the amplitude stabilization circuit to construct the Wien bridge oscillator of Figure 2.
Note any distortion in the output sine wave. To do this, you can measure the output in one channel of the oscilloscope and a sine waveform from the function generator on another channel. Match the amplitude and you can see the difference of the two waveforms.
Discuss your project (for example compare the hand calculation/simulation results; the things you learned, etc.) Try to answer the following questions in your discussion:
Why isn't an input signal source needed to obtain an output voltage signal?
When does the output waveform distort? Why?
Compare the operation of the two Wien bridge oscillator circuits. Comment on differences and similarities.
In the oscillator with the stabilizing circuit discuss the changes in the output waveform amplitude and shape during the pot's adjustment.
In the stabilized oscillator does the frequency change increase or decrease as the amplitude saturates? Explain why it changes.