The barkhausen criterion for oscillation pdf is a document that explains the theory behind the Barkhausen Criterian. It also includes a graph of the critical point and how it works.
An oscillator is an electrical circuit that aids in the conversion of DC to AC voltage. This article will explain what an oscillator is, the many kinds of oscillators, how they operate, the Barkhausen Criterian, its uses, and benefits and drawbacks.
What is an Oscillator, exactly?
Oscillators are electrical circuits that produce a sinusoidal or non-sinusoidal output signal, depending on the kind of Oscillator employed.
Figure 1: An Overview of Oscillators
It changes the waveform from DC to AC or periodic. Its circuits are often found in timepieces, computer clocks, radio receivers, and other electronic devices. Positive feedback and regenerative feedback are used in these circuits. The frequency of operation varies from less than 1 cycle per second to billions of cycles per second.
The fundamental block diagram of an oscillator is shown in Figure 2, which includes an oscillatory circuit, an amplifier, and a feedback network. The oscillatory circuit may be made of RC, LC, or quartz. An amplifier is a device that transforms DC to AC. Through the Feedback Network, the amplifier’s output is sent back into the Oscillatory circuit. The oscillations produced by the Oscillatory circuit serve as the amplifier’s input.
Figure 2: Oscillatory Circuit Block Diagram
Criteria of Barkhausen
It is defined as the criteria that every Electronic Circuit must meet in order to function as an Oscillator. According to the Barkhausen Criterion:
- The loop’s total gain is unity in magnitude.
- The loop’s overall phase shift is either zero or a multiple of 360 degrees.
Oscillators come in a variety of shapes and sizes.
They are categorized as follows:
- Oscillators with Feedback (Harmonic)
- Oscillators of Relaxation
Oscillators with Feedback (Harmonic)
Harmonic Oscillators are another name for feedback oscillators. A portion of the output is returned to the input without phase shift in this kind of Oscillatory circuit. An amplifier and a positive feedback circuit make up a feedback oscillatory circuit, which gives gain and causes phase shift, resulting in attenuation. Sinusoidal waves are generated using these Oscillatory circuits. There are two kinds of them. They are as follows:
- Oscillator RC
- Oscillator LC
Oscillator RC
Resistors and capacitors are used in this circuit, and the following RC oscillators are used:
- Oscillator of the Wien Bridge
- Oscillator with Phase Shift
Oscillator of the Wien Bridge
As illustrated in Fig.3, the amplifier’s output is applied between terminals a and c, which serves as the feedback network’s input. The diagonal terminals b and d, which are the output from the feedback network, provide the amplifier input. As a result, the amplifier provides its own input through the Wien Bridge feedback network.
The frequency of the Oscillator is determined by resistors and capacitors linked in series and parallel, which is known as a lead-lag network. The network takes the lead at lower frequencies and trails at higher frequencies.
Wien Bridge Oscillator (Fig. 3)
Oscillator with Phase Shift
Three high-pass filter circuits and an inverting amplifier are used in this design. It results in positive feedback and the necessary phase change. The feedback network receives its input from the inverting amplifier’s output. The feedback network’s output signal is fed into the amplifier, forming a loop with 3600 phase shift producing Oscillations.
Phase Shift Oscillator (Fig. 4)
Oscillator LC
Inductors and capacitors are used in this circuit. The following are examples of LC Oscillators:
- Oscillator Hartley
- Oscillator Colpitts
Oscillator Hartley
The tuned circuit, which consists of inductors and capacitors, determines the frequency of oscillations in this kind of Oscillator. The circuit diagram of a Hartley Oscillatory circuit is shown in Figure 5, where Rc is the collector resistor and Re is the emitter resistance. The voltage divider network is formed by the resistors R1 and R2. This circuit is comparable to that of a common-emitter amplifier.
The transistor begins to conduct when the power is turned on, increasing the collector current. This current aids in the charge of capacitors. The capacitors begin to discharge via inductors L1 and L2 after they have been charged to their full capacity. Oscillations in the Tank circuit are caused by charging and discharging cycles. The AC voltage produced by oscillation current is 180 degrees out of phase.
The amplifier’s output is used as an input across inductor L1, and the feedback voltage from L2 is supplied to the transistor’s base. The voltage of the Tank circuit is in phase with the output. This signal, which has a net phase shift of 3600, will be enhanced.
Hartley Oscillator (Fig. 5)
Oscillator Colpitts
A single stage inverting amplifier and an L-C phase shift network make up this circuit. It’s comparable to how most collectors are set up. The potential divider network is formed by connecting capacitors C1 and C2 in series to provide feedback voltage. The collector supply voltage Vcc is supplied to the transistor’s collector through a resistance RC, allowing maximal current flow through the transistor. Dc current flow to the tank circuit is prevented by coupling capacitor Cc in the output circuit.
Through coupling capacitor CC, the output of the phase-shift L-C network is linked from the junction of L and C2 to the amplifier input at base, preventing dc but providing a route to ac. A 180° phase change is produced by the transistor, and another 180° phase shift is produced via capacitive feedback. As a result, a net phase shift of 360° is achieved, which is required for oscillation generation.
The oscillations are applied to the transistor’s Base-Emitter junction and amplified. The tank circuit receives the amplified output, which guarantees undamped oscillations.
Colpitts Oscillator (Fig. 6)
Oscillators of Relaxation
To produce a waveform, this device utilizes an RC timing circuit driven by a Schmitt trigger. A square wave or a non-sinusoidal waveform is produced as a consequence.
What is the Function of an Oscillator?
Consider the Feedback Oscillatory Circuit in Figure 1 to better grasp the operating concept of an oscillator. As we know, a portion of the output voltage is returned to the in-phase input in this circuit. This is an in-phase situation. The output voltage is generated by amplifying the feedback voltage, and a portion of this value is used as input to the feedback circuit. The feedback voltage generated by this circuit is sent back to the input. This generates a loop, yielding a sinusoidal output waveform. Oscillation is the term for this.
S is a switch, while A is an amplifier in the circuit below. When the switch is open, there is no oscillation. If Vi is the input voltage, then V0 = AvVi is the output value, and V0= Vf is the voltage that is supplied back to the circuit when the circuit is closed. If Vf = Vi, the output voltage exists even when the input voltage is not there.
Av stands for Loop Gain and is equivalent to one. As a result, if Loop Gain is equal to 1, Oscillations may be produced at the output when input voltage is withdrawn from a closed circuit.
Figure 7: Working Principle Representation
Oscillator Applications
Among the applications are:
- Sweep circuits are what they’re utilized for.
- In digital systems, they are used to produce clocks.
- Radio transmitters and receivers utilize them extensively.
- They’re common in computers, counters, timers, and oscilloscopes.
The Benefits of Oscillators
The following are some of the advantages:
- The output of the Wien Bridge Oscillator is extremely steady and low distorted.
- It is possible to change the frequency of oscillation.
- There is less noise generated.
- They may be made at a cheap price.
Oscillators Have Drawbacks
The following are the drawbacks:
- Designing a Colpitts Oscillator is difficult.
- Stability of phase shift frequency The oscillator isn’t very good.
- The magnitude of LC circuit oscillations is difficult to regulate.
- As the value and size of inductors increase, the Hartley Oscillator can no longer be utilized as a low frequency oscillator.
Keep an eye out for:
Also see: How to Calculate Slew Rate for OP-AMP, Square and Sinusoidal Waves Power Triangle, Types, PFC, Applications, and Advantages of Power Factor Working Principles, Voltage Sensitivity, Types, and Applications of Voltmeters Classification, Configuration, Applications, and Benefits of Transistors
The rc oscillator is a circuit that generates an alternating current. It works by charging and discharging a capacitor.
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Frequently Asked Questions
What are the conditions for Barkhausen criterion?
The Barkhausen criterion is a physical phenomenon that can be observed in some semiconductors. It is defined as the ratio of the current to the voltage across an insulator when a direct current (DC) is applied to it, and it varies with frequency.
What is Barkhausen criterion for condition of oscillation?
The Barkhausen criterion is a measure of the stability of a system. It is used to determine whether or not a system can be excited into oscillation.
What is the significance of Barkhausen criterion?
The Barkhausen criterion is a physical property of an oscillator. It is the minimum voltage required to make the oscillator start oscillating in one direction and then reverse its flow.
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