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This presentation provides an overview of oscillators. It begins with an introduction and classification of oscillators. It then describes several common oscillator circuits including the tuned collector oscillator, Hartley oscillator, Colpitts oscillator, RC phase shift oscillator, and Wein bridge oscillator. Characteristics of each circuit like the feedback mechanism and frequency of oscillation are explained. Applications of oscillators in communication and electronics are mentioned. Key oscillator concepts like gain, feedback, and the Barkhausen criteria for sustained oscillations are also covered.
Presentation1
- 1. FET GKV A PRESENTATION ON OSCILLATORS Submitted To:- Submitted By:- Mr. Yogesh Kumar Navjyoti Sharma Assistant Professor B.TECH II YEAR Electrical Engineering Electrical Engineering
- 2. Introduction Classification of Oscillators Tuned Collector Oscillator Hartley Oscillator Colpitts Oscillator RC Phase Shift Oscillator Wein Bridge Oscillator Crystal Oscillator Application of Oscillator
- 3. Oscillation means that an effect that repeatedly and regularly fluctuates about the mean value. Oscillator is 1) An electronic circuit that generates a periodic waveform on its output without an external signal source. 2) It converts dc noise/signal power to its ac equivalent. 3) Oscillator requires a positive feedback(regenerative feedback). Sine wave Square wave Sawtooth wave
- 4. 1) INPUT OUTPUT NO INPUT OUTPUT BIAS BIAS 2) In amplifiers Negative feedback employed, while in oscillators positive feedback employed. Amplifier Oscillator
- 5. Gain of oscillators with feedback : A(f)= 𝐀 𝟏−𝐀𝛃 Where A is forward path gain β is feedback gain Aβ is loop gain For the sustained oscillations the necessary and sufficient conditions are : 1) The loop gain (Aβ) should be greater then or equal to unity (Aβ>1) 2) The net phase shift around the loop must be 2ᴫ or integer multiple of 2ᴫ. These two condition are known as Barkhausen criterion.
- 6. Oscillators are classified as follows:- 1) According to output waveform 2) According to components used 3) According to frequency range According to output waveform oscillators are classified into two ways I. Sinusoidal Oscillators: If the generated waveform is sinusoidal or close to sinusoidal (with a certain frequency) then the oscillator is said to be a Sinusoidal Oscillator. Example: Hartley Oscillator, Colpitts oscillator, Wein Bridge Oscillator etc. II. Non Sinusoidal Oscillators ( Relaxation Oscillators): If the output waveform is non-sinusoidal, which refers to square/saw-tooth waveforms, the oscillator is said to be a Relaxation Oscillator. Example: Triangular Wave Generator, Square Wave Generator etc.
- 7. According to Components used I. LC Oscillators II. RC Oscillators According to frequency range
- 8. A TUNED COLLECTOR diagram as shown below: In this oscillator 2ᴫ phase shift is achieved by transistor and transformer. It is called tuned oscillator because the LC tuned circuit is connected at the collector. The oscillation frequency is given by: f= 1 2𝜋√𝐿𝐶
- 9. The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tank circuit consisting of capacitors and inductors, that is, an LC oscillator. In Hartley oscillator 2𝜋 phase shift can be achieved by transistor which gives 180° phase shift while remaining 180° phase shift is achieved by tapped inductors. The frequency of oscillation is given by: f˳= 1 2𝜋 𝐿(𝑒𝑞)𝐶 where L(eq) =L1+L2+2M If mutual inductance(M) is neglected then L(eq) = L1+L2
- 10. The Colpitts oscillator is a type of oscillator that uses an LC circuit in the feedback loop. The feedback network is made up of a pair of tapped capacitors (C1 and C2) and an inductor L to produce a feedback necessary for oscillations. In Colpitts oscillator 2𝜋 phase shift can be achieved by transistor which gives 180° phase shift while remaining 180° phase shift is achieved by tapped capacitors. The frequency of oscillation is given by: f˳= 𝟏 𝟐𝝅√𝑪(𝒆𝒒)𝑳 where C(eq)= 𝐶1×𝐶2 𝐶1+𝐶2
- 11. The L-C oscillators are not employed at low frequencies because at low frequencies the inductors become large and bulky, hence R-C oscillators are used. The feedback network is made up of a R-C section to produce a feedback necessary for oscillations. In R-C phase shift oscillator 2𝜋 phase shift can be achieved by transistor which gives 180° phase shift while remaining 180° phase shift is achieved by a R-C phase shift network consist three R-C section. The frequency of oscillation is given by: f˳= 1 2𝜋𝑅𝐶√6+4( 𝑅(𝐿) 𝑅) where R(L)= Load or output resistance
- 12. Wein Bridge oscillator consists a balanced wein bridge for the feedback network. It also consists two stage amplifier because feedback network provide 0° phase shift. In Wein Bridge oscillator 2ᴫ phase shift is achieved by two stage amplifier. The frequency of oscillation is given by: f˳= 1 2𝜋√𝑅1𝑅2𝐶1𝐶2 If R1=R2=R and C1=C2=C then f˳= 1 2𝜋√𝑅𝐶
- 13. Certain crystals like Quartz, Rochelle salt etc. are used for the construction of crystal oscillator. Its operation is based on the piezoelectric effect i.e. when an a.c. voltage is applied to such crystal its mechanically vibrated ( compressed or stretched) and vice versa.
- 14. Electrical Equivalent of Crystal Oscillator: From the fig. it is clear that there is two resonance a) Series Resonance b) Parallel Resonance a) Series Resonance: Occurs due to series capacitor and series inductor. The series resonance frequency is given as f˳= 1 2𝜋√𝐿𝐶
- 15. b) Parallel Resonance: Occurs due to series branch(L1-C1-R1) and parallel capacitor (C0). The parallel resonance frequency is given by: fp= 1 2𝜋√ 1 𝐿 1 𝑐 + 1 𝐶𝑜 The parallel resonance frequency is always greater than series resonane frequency.
- 16. The Crystal oscillator with transistor with impedance curve is shown as: The crystal oscillator gives maximum feedback voltage at parallel resonance frequency because at this frequency its impedance is maximum.
- 17. Oscillators are commonly used in communication circuits. All the communication circuits for different modulation techniques—AM, FM, PM—the use of an oscillator is must. Oscillator circuits are used in computer peripherals, counters, timers, calculators, phase-locked loops, digital multimetres, oscilloscopes, and numerous other applications.