oscillator presentation ucet
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The document discusses different types of oscillators: 1. Oscillators produce specific periodic waveforms like square, triangular, sawtooth, and sinusoidal waves using active and passive devices like resistors, capacitors, and inductors. 2. There are two main classes of oscillators: harmonic oscillators and relaxation oscillators. 3. A sinusoidal oscillator consists of an amplifier with part of its output fed back to the input in a feedback loop. The Barkhausen criterion must be satisfied for oscillations to occur.
oscillator presentation ucet
- 3. Oscillator Oscillators are circuits that produce specific, periodic waveforms such as square, triangular, saw tooth, and sinusoidal. They use some form of active device and passive device like resistor capacitor and inductor.
- 4. Oscillation Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states.
- 5. Classification of Oscillator There are two main classes of oscillators. Harmonic Oscillator Relaxation Oscillator
- 6. Sinusoidal Oscillator The oscillator which gives a sinusoidal wave form is called a sinusoidal oscillator.
- 7. Basic Principle A sinusoidal oscillator generally consists of an amplifier having part of its output returned to the input by means of a feedback loop.
- 8. Barkhausen Criterion For oscillation the Barkhausen Criterion must be equal to 1. Aβ = 1 we can write a complex phasor Aβ(jω) ‹ which can be also written as |Aβ| θ where |Aβ| is the loop gain magnitude and θ is the phase shift.
- 9. Barkhausen criterion requires that |Aβ|= 1 and θ=±360⁰n where n is any integer. So in polar and rectangular form , the Barkhausen criterion is expressed as Aβ(jω)=1‹±360⁰n = 1+j0
- 10. Harmonic Oscillator Harmonic Oscillators generate complex waveforms, such as square, rectangular and saw tooth.
- 11. Basic Principle It contains an energy storing element(capacitor or an inductor) and a nonlinear trigger circuit that periodically charges and discharges the energy stored in the storage element thus causing abrupt changes in the output waveform.
- 12. The Wien Bridge Oscillator is so called: because the circuit is based on a frequency- selective form of the Whetstone bridge circuit. The Wien Bridge oscillator is a two-stage RC coupled amplifier circuit that has good stability at its resonant frequency, low distortion and is very easy to tune making it a popular circuit as an audio frequency oscillator.
- 18. It can be seen that at very low frequencies the phase angle between the input and output signals is "Positive" (Phase Advanced), while at very high frequencies the phase angle becomes "Negative" (Phase Delay). In the middle of these two points the circuit is at its resonant frequency, (ƒr) with the two signals being "in-phase" or 0o.
- 19. Wien Bridge Oscillator Summary Then for oscillations to occur in a Wien Bridge Oscillator circuit the following conditions must apply. 1. With no input signal the Wien Bridge Oscillator produces output oscillations. 2. The Wien Bridge Oscillator can produce a large range of frequencies. 3. The Voltage gain of the amplifier must be at least 3. 4. The network can be used with a Non-inverting amplifier. 5. The input resistance of the amplifier must be high compared to R so that the RC network is not overloaded and alter the required conditions.
- 20. The RC Oscillator The phase angle between the input and output signals of a network or system is called phase shift. In a RC Oscillator the input is shifted 180o through the amplifier stage and 180o again through a second inverting stage giving us "180o + 180o = 360o" of phase shift which is the same as 0o thereby giving us the required positive feedback. In other words, the phase shift of the feedback loop should be "0".
- 21. In a Resistance-Capacitance Oscillator or simply an RC Oscillator, we make use of the fact that a phase shift occurs between the input to a RC network and the output from the same network by using RC elements in the feedback branch, for example.
- 23. Then by connecting together three such RC networks in series we can produce a total phase shift in the circuit of 180o at the chosen frequency and this forms the bases of a "phase shift oscillator" otherwise known as a RC Oscillator circuit.
- 24. The Quartz Crystal Oscillators One of the most important features of any oscillator is its frequency stability, or in other words its ability to provide a constant frequency output under varying load conditions. Some of the factors that affect the frequency stability of an oscillator include: temperature, variations in the load and changes in the DC power supply. Frequency stability of the output signal can be improved by the proper selection of the components used for the resonant feedback circuit including the amplifier but there is a limit to the stability that can be obtained from normal LC and RC tank circuits. To obtain a very high level of oscillator stability a Quartz Crystal is generally used as the frequency determining device to produce another types of oscillator circuit known generally as a Quartz Crystal Oscillator, (XO).
- 25. The quartz crystal used in a Quartz Crystal Oscillator is a very small, thin piece or wafer of cut quartz with the two parallel surfaces metallised to make the required electrical connections. The physical size and thickness of a piece of quartz crystal is tightly controlled since it affects the final frequency of oscillations and is called the crystals "characteristic frequency". Then once cut and shaped, the crystal can not be used at any other frequency. In other words, its size and shape determines its frequency. The crystals characteristic or resonant frequency is inversely proportional to its physical thickness between the two metallised surfaces. A mechanically vibrating crystal can be represented by an equivalent electrical circuit consisting of low resistance, large inductance and small capacitance as shown below.
- 26. l
- 27. The equivalent circuit for the quartz crystal shows an RLC series circuit, which represents the mechanical vibrations of the crystal, in parallel with a capacitance, Cp which represents the electrical connections to the crystal. Quartz crystal oscillators operate at "parallel resonance", and the equivalent impedance of the crystal has a series resonance where Cs resonates with inductance, L and a parallel resonance where L resonates with the series combination of Cs and Cp as shown. Crystal reactance:
- 28. The slope of the reactance against frequency above, shows that the series reactance at frequency ƒs is inversely proportional to Cs because below ƒs and above ƒp the crystal appears capacitive, i.e. dX/dƒ, where X is the reactance. Between frequencies ƒs and ƒp, the crystal appears inductive as the two parallel capacitances cancel out. The point where the reactance values of the capacitances and inductance cancel each other out Xc = XL is the fundamental frequency of the crystal.
- 29. Relaxation oscillator • The oscillator which shows square wave, saw tooth wave, triangular wave and pulse wave in his o/p instead of sine wave is called relaxation oscillator.
- 31. Shockley diode relaxation oscillator • The oscillator circuit which consists of Shockley diode and we have sawtooth wave in its o/p is called Shockley diode relaxation oscillator. • As shown in Fig A and B
- 32. Circuit diagram of Shockley diode relaxation oscillator A B
- 33. Circuit diagram with wave shape A B
- 34. Working of Shockley diode relaxation oscillator Switch close Capacitor charging Voltage reached VBR(F) Diode conducting mode Capacitor discharging Holding current Diode off Capacitor charging Capacitor charging time A-B Discharging time B-C
- 36. Charging time Tch=RC Loge(v/v-vs) Frequency F=1/Tch=1/RC Loge(v/v-vs) R’s Max & Min values Rmax = v-vH/IH Rmin = V-Vs/Is
- 40. Group members