Explain the working principle of a Wien bridge oscillator using transistors or op-amps.
1 Answer
A Wien bridge oscillator is a type of electronic oscillator circuit that generates sinusoidal waveforms at a specific frequency. It can be implemented using either transistors or operational amplifiers (op-amps). Here, I'll explain the working principle of the Wien bridge oscillator using both approaches.
Wien Bridge Oscillator with Transistors:
The basic configuration of a transistor-based Wien bridge oscillator consists of two stages: an amplifier stage and a feedback network. The feedback network consists of a series combination of resistors and capacitors forming a bridge configuration, and this bridge network is responsible for producing the desired oscillation.
The main components of the oscillator are as follows:
Transistor amplifier stage: This stage amplifies the signal and provides gain to compensate for the signal loss in the feedback network. It typically employs a common-emitter configuration.
Feedback network (Wien bridge): This network consists of two resistors (R1 and R2) and two capacitors (C1 and C2) connected in a bridge configuration. The two capacitors are connected in parallel to form one arm of the bridge, while the two resistors are connected in series to form the other arm.
Now let's understand the working principle of the Wien bridge oscillator:
Initially, the circuit starts with some noise or small signal at its input.
The amplified signal from the transistor amplifier stage is fed into the feedback network.
The feedback network acts as a frequency-selective filter. At a certain frequency (the desired oscillation frequency), the phase shift around the loop becomes zero, and the circuit satisfies the Barkhausen criteria for oscillation.
When the phase shift around the loop is 0 degrees and the overall gain is equal to or greater than unity, the circuit will sustain oscillations at the desired frequency.
The frequency of oscillation is determined by the RC values in the feedback network and is given by f = 1 / (2 * π * R * C), where R is the total resistance of the bridge network (R = R1 + R2) and C is the total capacitance of the bridge network (C = C1 * C2 / (C1 + C2)).
The Wien bridge oscillator will naturally settle at the frequency determined by the values of resistors and capacitors in the feedback network.
Wien Bridge Oscillator with Op-Amps:
When using op-amps, the basic configuration of the Wien bridge oscillator is similar, but it becomes more straightforward and precise to implement. The op-amp provides high gain, and its feedback network is usually an RC network rather than a bridge network.
The main components of the op-amp based Wien bridge oscillator are:
Op-amp: The op-amp provides high gain and acts as the amplifier in the circuit.
Feedback network: The feedback network consists of two resistors (R1 and R2) and two capacitors (C1 and C2) connected in an RC bridge configuration.
The working principle of the op-amp based Wien bridge oscillator is similar to the transistor-based one:
The op-amp amplifies the input signal and feeds it into the RC feedback network.
The feedback network acts as a frequency-selective filter. At the desired oscillation frequency, the phase shift around the loop becomes zero, and the circuit satisfies the Barkhausen criteria for oscillation.
The frequency of oscillation in this case is given by f = 1 / (2 * π * R * C), where R is the total resistance of the RC network (R = R1 + R2) and C is the total capacitance of the RC network (C = C1 * C2 / (C1 + C2)).
The circuit will oscillate at the frequency determined by the values of resistors and capacitors in the feedback network.
It's important to note that in both cases (transistor-based and op-amp-based Wien bridge oscillators), the amplitude of the oscillations can be controlled using an amplitude stabilization circuit. This ensures that the output waveform remains stable and at a consistent amplitude.
Wien Bridge Oscillator with Transistors:
The basic configuration of a transistor-based Wien bridge oscillator consists of two stages: an amplifier stage and a feedback network. The feedback network consists of a series combination of resistors and capacitors forming a bridge configuration, and this bridge network is responsible for producing the desired oscillation.
The main components of the oscillator are as follows:
Transistor amplifier stage: This stage amplifies the signal and provides gain to compensate for the signal loss in the feedback network. It typically employs a common-emitter configuration.
Feedback network (Wien bridge): This network consists of two resistors (R1 and R2) and two capacitors (C1 and C2) connected in a bridge configuration. The two capacitors are connected in parallel to form one arm of the bridge, while the two resistors are connected in series to form the other arm.
Now let's understand the working principle of the Wien bridge oscillator:
Initially, the circuit starts with some noise or small signal at its input.
The amplified signal from the transistor amplifier stage is fed into the feedback network.
The feedback network acts as a frequency-selective filter. At a certain frequency (the desired oscillation frequency), the phase shift around the loop becomes zero, and the circuit satisfies the Barkhausen criteria for oscillation.
When the phase shift around the loop is 0 degrees and the overall gain is equal to or greater than unity, the circuit will sustain oscillations at the desired frequency.
The frequency of oscillation is determined by the RC values in the feedback network and is given by f = 1 / (2 * π * R * C), where R is the total resistance of the bridge network (R = R1 + R2) and C is the total capacitance of the bridge network (C = C1 * C2 / (C1 + C2)).
The Wien bridge oscillator will naturally settle at the frequency determined by the values of resistors and capacitors in the feedback network.
Wien Bridge Oscillator with Op-Amps:
When using op-amps, the basic configuration of the Wien bridge oscillator is similar, but it becomes more straightforward and precise to implement. The op-amp provides high gain, and its feedback network is usually an RC network rather than a bridge network.
The main components of the op-amp based Wien bridge oscillator are:
Op-amp: The op-amp provides high gain and acts as the amplifier in the circuit.
Feedback network: The feedback network consists of two resistors (R1 and R2) and two capacitors (C1 and C2) connected in an RC bridge configuration.
The working principle of the op-amp based Wien bridge oscillator is similar to the transistor-based one:
The op-amp amplifies the input signal and feeds it into the RC feedback network.
The feedback network acts as a frequency-selective filter. At the desired oscillation frequency, the phase shift around the loop becomes zero, and the circuit satisfies the Barkhausen criteria for oscillation.
The frequency of oscillation in this case is given by f = 1 / (2 * π * R * C), where R is the total resistance of the RC network (R = R1 + R2) and C is the total capacitance of the RC network (C = C1 * C2 / (C1 + C2)).
The circuit will oscillate at the frequency determined by the values of resistors and capacitors in the feedback network.
It's important to note that in both cases (transistor-based and op-amp-based Wien bridge oscillators), the amplitude of the oscillations can be controlled using an amplitude stabilization circuit. This ensures that the output waveform remains stable and at a consistent amplitude.