ECE 3274 LAB 3 Project – Sinusoidal Oscillator
Revised: Fall 2008 1 of 6
Project – Sinusoidal Oscillator
Objective: This project will demonstrate the basic operation and design of a Wien
bridge RC oscillator.
Components: 741 op-amp, 1N4001 diode (2), 2N7000 MOSFET
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 with a positive feedback loop of 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.
Av
β
Rload
Av = Non-inverting amplifier
β = positive feedback transfer function
І Loop gain І = І (Av)(β) І = 1
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:
RC
f
2
1
0
When:
2
1
2
R
R
