Collector-to-base feedback is provided by coil L2 in transformer T1. Coil L2, with a smaller number of turns than L1, is inductively couple to L1 by transformer action.
The necessary zero phase shift around the feedback loop can be obtained by adjusting trimmer capacitor C1. If loop gain exceeds unity at the tuned frequency, the circuit will oscillate. Loop gain is determined by the turns ratio of L1 with respect to L2 in transformer T1. Because the circuit in Fig. The circuit can be enhanced to oscillate at frequencies from less than Hz to UHF Ultra High Frequency frequencies with a laminated iron-core transformer.
The same circuit will oscillate satisfactorily in the UHF regions with an air-core transformer. Classic LC Oscillators: Figure 6 illustrates the Hartley Oscillator , which is a variation of the tuned-collector oscillator that was shown in Fig. This oscillator is recognizable by the tapped coil in its tuned resonant circuit. Oscillation of the Hartley oscillator circuit depends on phase-splitting autotransformer action of the tapped coil in the tuned resonant circuit.
The positive power supply is connected to the tap to obtain the necessary autotransformer action. The signal from the top of the coil is coupled to the base input of Q1 through isolating capacitor C2. The oscillator will oscillate at a center frequency determined by its LC product. The Colpitts Oscillator shown in Fig. It is identified by the voltage divider in its tuned resonant circuit.
With the component values shown, this Colpitts circuit will oscillate at about 37KHz. Capacitor C1 is in parallel with the output capacitance of Q1, and C2 is in parallel with the input capacitance of Q1. This shift can be minimized for high frequency stability by selecting values of C1 and C2 that are relative to the internal capacitances of Q1.
The Clapp Oscillator , a modification of the Colpitts oscillator, shown in Fig. This is achieved by adding capacitor C1 in series with the coil in the tuned resonant tank circuit.
It is selected to have a value that is small with respect to C2 and C3. As a result of the presence of this capacitor, the resonant frequency of the tank and oscillator will be determined primarily by the values of L1 and C1. With the component values shown, the Clapp oscillator oscillates at about 80KHz. Figure 9 shows the classic Reinartz Oscillator. In this circuit, tuning coil L1 in the collector circuit and the tuning coil L2 in the emitter circuit are inductively coupled to tuning coil L3 in the resonant tank circuit.
Positive feedback is obtained by coupling the collector and emitter signals of the transistor through windings L1 and L2, and inductively coupling both of these coils to L3. This Reinartz oscillator oscillates at a frequency determined by L3 and trimmer capacitor C2. With the values and turns ratios given in Fig.
Modulation: The LC oscillator circuits shown in Figs. Figure 10 is the schematic for a beat-frequency oscillator BFO. It is based on the tuned-collector circuit of Fig. The value of emitter-decoupling capacitor C1 was selected to present a low impedance to the KHz carrier signal, while also presenting a high impedance to the low-frequency modulation signal. Figure 11 shows how the BFO circuit in Fig. Tuning is adjusted by trimmer potentiometer R5.
Silicon diode D1 functions as an inexpensive varactor diode. Astable Oscillators: Conventional oscillator circuits produce sinewaves, but repetitive square waves are important in electronics. One way to generate them is with the astable multivibrator circuit shown in Fig. This multivibrator is a self-oscillating regenerative switch whose on and off periods are controlled by the time constants obtained as the products of R2 and C2, and R3 and C1.
The waveforms taken at the collector and base of transistors Q1 and Q2 are shown in Fig. The frequency of the astable multivibrator in Fig. The frequency can be varied with dual-gang variable resistors placed in series with 10K limiting resistors in place of R2 and R3.
The operating frequency can, if required, be synchronized to that of a higher-frequency signal by coupling part of the external signal into the timing networks of the astable circuit. Outputs can be taken from either collector of the circuit, and the two outputs are in opposite in phase. The upper voltage limit is set by inherent transistor behavior: as the transistors change state at the end of each half-cycle, the base-emitter junction of one transistor is reverse biased by a voltage that is about equal to the supply voltage.
Consequently, if the supply voltage exceeds the reverse base-emitter breakdown voltage of the transistor, circuit timing will be affected. This characteristic can be overcome with the circuitry modifications shown in Fig. A silicon diode is connected in series with the base input terminal of each transistor to raise the effective base-emitter reverse breakdown voltage of each transistor to a value greater than that of the diode. The oscillator is available according to the need of frequency for a particular application.
For example, for audio frequency application the oscillator used will be audio frequency oscillator. This is because the waveforms generated by it will consist of audio frequencies. The working mechanism of sinusoidal and non-sinusoidal oscillators differs widely, the sinusoidal oscillator use resonance for generating sinusoidal waveform while non-sinusoidal oscillator uses switching principle for generation of the non-sinusoidal waveform. Usually, multivibrators are used for generation of the non-sinusoidal waveform.
Similar, to the amplifier, the oscillator also does not have its own energy but using energy conversion it can generate the waveforms of desired amplitude and frequency. The DC source connected to oscillator provides DC power to it; the oscillator converts this DC power into AC power and generates waveforms of definite frequency.
The condition for the oscillator to generate waveforms is fixed. The oscillations will start when the phase shift across the complete loop will become zero. And the frequency at which this happens will be the oscillating frequency.
Another crucial condition for generation of oscillations will be that the gain of this closed loop circuit should be greater than or equal to unity. The amplifier and oscillator both are the crucial circuits which hold special significance not only in electronics circuit but also in communication circuitry. The major difference between their working mechanisms differentiates these two circuits. The amplifier is significant for increasing the intensity of the weak signal. While the oscillator is significant for providing AC signal source to an electronic circuit.
Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Key Difference Between Amplifier and Oscillator The factor which creates the key difference between amplifier and oscillator is that amplifier is used as a circuit to amplify the signal.
An astable multivibrator [also known as an oscillator] is a circuit built so that it does not come to rest in one single state but switches between them continuously. Paul Vigoureux has written: 'Quartz resonators and oscillators' -- subject s : Crystal Oscillators, Electric resonators, Quartz crystals 'Quartz vibrators and their applications' 'Units and standards for electromagnetism' -- subject s : Electromagnetism, Units, Units of measurement 'Quartz oscillators and their applications' -- subject s : Crystal Oscillators, Electric Oscillators, Electric resonators, Pyroelectricity, Quartz.
The advantages of oscillators is that they have good stability at high frequency and have a good wave purity. The disadvantage is that it is hard to design. To create oscillators An LM IC contains operational amplifiers. LM ICs can be used for different purposes in circuits, such as oscillators, rectifiers or oscillators as well. They are not suitable for use as extremely low-frequency oscillators because the inductors and capacitors would be large in size, heavy, and costly to manufacture.
Difference between spirogyra and mushroom. Boris Aleksandrovich Glebov has written: 'Bloking-generatory na tranzistorakh' -- subject s : Blocking oscillators, Transistor Oscillators. RC phase shift oscillators are used for musical instruments, oscillators, voice synthesis, and GPS units. They work at all audio frequencies. Log in. The Difference Between. Waves Vibrations and Oscillations. Study now. See Answer. Best Answer. Oscillator is an electronic circuit which can generate oscillating sin signal without any oscillating input with use of positive feedback Multivibrator is a two stage RC coupled amplifier circuit which can generate squae signal without ac input.
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