BJT Phase Shift Oscillator Online Calculator

Phase shift oscillator is one of many types of sinusoidal oscillator. Phase shift oscillator can be designed using FET, BJT transistors or operational amplifier. The following is BJT based phase shift oscillator online calculator that can be used to calculate the resistor value given the resonant frequency, the collector resistor value and the capacitor value of the feedback network.

Resistor(R) Calculator

Formula Used:
\(f_{r}=\frac{b (+/-) \sqrt{b^2-4ab}}{2a} \) \(\\\)where, \(a = 6 (2\pi f_r)^2 C^2\) , \(b = 4 R_C (2\pi f_r)^2 C^2\) , \(c = -1\);

Theoretical Results:

LCR series resonant circuit diagram

The above Phase Shift Oscillator is made up of BJT amplifier and the feedback circuit. The BJT is biased or DC stabilized using voltage divider biasing method. The resistors R1 and R2 forms the voltage divider that sets the base voltage at the selected bias point. The capacitor CE is the bypass capacitor. The feedback network consist of three stages of RC filter each of which creates a 60 degree phase shift of the output signal of the amplifier. With three RC filter the total phase shift is 180 degree which is required for oscillation. 

This type of oscillator are used in making stable, less distortion and low frequency sinusoidal signals. The circuit is also not complex and therefore simple to design compared to other oscillator. The difficulty in making this oscillator is that the feedback signal magnitude is low and hence oscillation is difficult to obtain without high enough power supply. The stability of the oscillation is moderate. There are also some advantage of Phase shift oscillator over LC oscillator. Since Phase Shift oscillator uses resistor compared to inductors in LC oscillator the phase shift oscillator are more stable and less bulky compared in LC oscillator. 

The frequency of oscillation of the transistolized oscillator is given by,

\(f_r = \frac{1}{2 \pi R C \sqrt{6}}\)

where, \(R=R_1=R_2=R_3\) and \(C=C_1=C_2=C_3\)

The feedback fraction B of the phase shift oscillator is 1/29 which means the closed loop gain \(A_{CL}\) must be 29. So if \(v_o\) is oscillator output and \(v_f\) is the feedback signal then we have,

\(v_f = B v_o = \frac{v_o}{29}\)

and also,

\(v_o = A_{CL} v_f = 29 v_f\)

There are other oscillator types such as Colpitts oscillator, Hartley oscillator, Wien Bridge oscillator. The Online Oscillator Calculator contains these oscillator calculators. 

Many times in designing oscillator we need LC based oscillators. Following are LC based calculator for oscillator design.

Some of the tutorials of designing oscillators are as follows.

Some practical oscillator design on breadboard is as follows.


Post a Comment

Previous Post Next Post