A phase shift oscillator is a type of electronic circuit that generates a
sine wave output signal. It is a type of LC oscillator that uses a
combination of passive and active components to generate a sine wave
output. The 2N2222 transistor is a common choice for building a phase
shift oscillator circuit, due to its high gain and low noise
characteristics.
There are many ways to make oscillator such as Wien bridge oscillator, LC circuit based oscillator like Hartley oscillator and Colpitts oscillator, crystal oscillator and there is Phase Shift Oscillator. The circuit of a phase shift oscillator is relatively simple, consisting of a transistor, resistors, and capacitors. The 2N2222 transistor is used as an amplifier to amplify the input signal and generate the output signal. The resistors and capacitors are used to create a feedback loop that maintains the oscillation of the circuit.
The following is the circuit diagram of phase shift oscillator build with 2N2222 transistor.
The circuit works by applying a small input signal to the base of the 2N2222 transistor. The transistor amplifies the input signal and applies it to the collector. The output signal is then fed back to the base through the resistors and capacitors. This creates a feedback loop that maintains the oscillation of the circuit.
The output frequency of the oscillator can be adjusted by changing the values of the resistors and capacitors. The frequency can also be adjusted by changing the bias current of the transistor, which can be done by changing the value of the base resistor.
This RC phase shift oscillator is build to generate sine wave of frequency of 800Hz. An oscillator has basically two parts- an amplifying part and a feedback part. The signal starts to generates on its own due to noise, which gets amplified by the amplifier. The feedback part provides necessary phase shift to the output of the amplifying part such that the phase shift around the whole system is 0 degree or 360 degree.
In the above phase shift oscillator, the BC2222 along with the basing part(R4,RV2 and RV1) forms the amplifying part of the oscillator. The feedback part is formed by the three resistors R1, R2 and R3 and the capacitors C1, C2 and C3. This RC feedback network provides the necessary 180 degree phase shift to the output signal from the amplifier such that overall phase shift from input to output of the system is exactly 0 degree or 360 degree. Also the values of these resistors and capacitors determines the frequency of oscillation is given by the following equation.
\[f_r = \frac{1}{2 \pi RC \sqrt{2 N}}\]
where, \(f_r\) is the resonant frequency, R=R1,R2,R3 and C=C1,C2,C3 and N is the number of RC stages. R=R1=R2=R3=10KOhm, C=C1=C2=C3=10nF and N= 3 in this case.
See the online oscillator calculator for calculating the values of R and C for particular frequency.
Due to thermal noise, signal will enter the base of the 2N2222 transistor and gets amplified by the transistor. The amplified signal appears at the collector of the transistor. Let' say the amplification is A. Then the output signal at the collector enters into the RC feedback network and there will be loss of signal while going through the feedback path. Let say the feedback fraction is \(\beta\). Then for compensation of the loss due to feedback and therefore oscillation to occur the following equation must hold.
\[ A \beta \geq 1\]
In the above circuit diagram the gain of the amplifier is controlled with the variable resistor RV1.
One of the advantages of using a 2N2222 transistor in a phase shift oscillator circuit is that it has a high gain and a low noise figure. This means that the circuit will have a high signal-to-noise ratio and will generate a clean output signal.
Another advantage of using a 2N2222 transistor is that it is widely available and inexpensive. This makes it an ideal choice for building a phase shift oscillator circuit.
In conclusion, the 2N2222 transistor is a popular choice for building a phase shift oscillator circuit due to its high gain and low noise characteristics. The circuit is relatively simple and easy to build, and the output frequency can be easily adjusted by changing the values of the resistors and capacitors. Additionally, the 2N2222 transistor is widely available and inexpensive, making it an ideal choice for hobbyists and DIY projects.
If you are interested in Phase Shift Oscillator design then also see another BJT phase shift oscillator BC547 Transistor Phase Shift Oscillator.
