Tuned Oscillators Pdf To Doc

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An oscillator is one kind of an electronic circuit that generates an oscillating, periodic electronic signal such as a sine wave (or) a square wave. The main function of an oscillator is to convert DC (direct current) from a power supply to an AC (alternating current) signal. These are widely used in several electronic devices. General examples of signals produced by oscillators comprise signals broadcast by the transmitters of a TV and a radio transmitter, CLK signals that control the quartz clocks and computers. The sounds generated by video games and electronic beepers. The oscillator is often characterized by the output signal’s frequency. Oscillators are mainly designed to generate an output of high-power AC from a direct current supply that is frequently called inverters.

The different types of oscillators have the same functions, that they generate continuous undamped o/p. But, the main difference between the oscillators lies in the method by the energy which is supplied to the tank circuit to meet up the losses. The common types of transistor oscillators mainly include tuned collector oscillator, Colpitt’s oscillator, Hartley, phase shift, Wein bridge and a crystal oscillator

  • Oscillators, the current consumption increases significantly. Tuning-fork crystals typically have a frequency range of 10 kHz to 200 kHz in fundamental mode and a maximum drive level of 1 µW. These parameters make them the first choice for the 32768-Hz ultra-low-power crystal oscillator in MSP430 microcontrollers.
  • The harmonic, or linear, oscillator produces a sinusoidal output. There are two types: Feedback oscillator. The most common form of linear oscillator is an electronic amplifier such as a transistor or operational amplifier connected in a feedback loop with its output fed back into its input through a frequency selective electronic filter to provide positive feedback.
  • Sinusoidal oscillators consist of amplifiers with external components used to generate oscillation, or crystals that internally generate the oscillation. The focus here is on sine wave oscillators, created using operational amplifiers op amps. Sine wave oscillators are used as references or test waveforms by many circuits.

OSCILLATORS 01.PDF 1 E. COATES 2007 -2013 Oscillators 1.0 Oscillator Basics Introduction These oscillator modules in Learnabout Electronics describe how many commonly used oscillators work, using discrete components and in integrated circuit form. Tuned Oscillators (Radio Frequency Oscillators) 17 Tuned oscillator is a circuit that generates a radio frequency output by using LC tuned (resonant) circuit. Because of high frequencies, small inductance can be used for the radio frequency of oscillation. Tuned-input and tuned-output Oscillator tuned-output tuned-input feedback coupling ci RF.


What is a Tuned Collector Oscillator ?

The tuned collector oscillator is one kind of transistor LC oscillator where the tank circuit comprises of a capacitor and a transformer, that is connected to the collector terminal of the transistor. The tuned collector oscillator circuit is the simplest & the basic kind of LC oscillators. The tank circuit connected in the collector circuit performs like a simple resistive load at resonance and decides the oscillator frequency. The general applications of this circuit include signal generators,RF oscillator circuits, frequency demodulators, mixers, etc. The circuit diagram and working of a tuned collector oscillator are discussed and shown in the following below.

Tuned Collector Oscillator Circuit

The circuit diagram of the tuned collector oscillator is shown below. For the transistor, the resistors R1, R2 form a voltage divider bias. The emitter resistor ‘Re’ is which is intended for thermal stability. It also stops the transistor’s collector current and the emitter bypass capacitor ‘Ce’. The main role of ‘Ce’ is to avoid improved oscillations. If the emitter bypass capacitor is not there, the amplified AC oscillations will fall across emitter resistor ‘Re’ and will add on to the ‘Vbe‘ base-emitter voltage of the transistor. And after this, this will change the conditions of DC biasing. In the circuit below, primary of the transformer L1 and capacitor C1 shapes the tank circuit.

Tuned Collector Oscillator Circuit Working

When the power supply is turned ON, the transistor gets the current and starts conducting. The ‘C1’ capacitor starts charging. When the C1 capacitor gets the charge, then the charge starts discharging through the primary coil L1 of the transformer.

When the capacitor C1 is fully discharged, the energy in the capacitor as the electrostatic field will be stirred to the inductor as the electromagnetic field. Now there will be no more voltage across the capacitor to maintain the current through the primary coil in the transformer starts to collapse. In order to resist this, the L1 coil generates a back emf which may charge the capacitor again. Then capacitor ‘C1’ discharges through the L1 coil and the series is constant. This charging & discharging sets up a sequence of oscillations in the tank circuit.


The oscillations generated in the tank circuit is fed back to the base terminal of the Q1 transistor by the minor coil by inductive coupling. The quantity of feedback can be regulated by changing the ratio twists of the transformer.

The direction of the secondary winding coil ‘L2’ is in such a way that the voltage across it will be 180° phase opposite to that of the voltage across the primary (L1). Therefore the feedback circuit generates 180° of phase shift and the Q1 transistor produces 180° of phase shift of another.As a result the total phase shift is acquired between input & output. It is an extremely required condition for positive feedback and continued oscillations.

The collector current (CC) of the transistor balances the lost energy in the tank circuit. This can be done by adopting a little amount of voltage from the tank circuit, strengthening it and applying it back to the circuit. The Capacitor ‘C1’ can be made variable in the applications of variable frequency.

In the tank circuit, the frequency of oscillations can be expressed using the following equation.

F = 1/ 2π√[(L1C1)]

In the above equation, ‘F’-denotes the frequency of oscillation and L1-is the inductance of the transformer’s primary coil and C1-is the capacitance.

Application of Tuned Collector Oscillator Circuit

The applications of tuned collector oscillator involves in the local oscillator of a radio. All transformers introduce 180º of a phase shift between primary & secondary.

Electronics receiver principles make use of an LC tuned circuit with the following

Oscillators

C1 = 300 pF and L1 = 58.6 μH

Frequency of oscillations can be calculated by the following procedure

C1 = 300 pF

= 300 × 10−12 F

L1 = 58.6 μH

= 58.6 × 10−6 H

Frequency of oscillations, f = 1/ 2π√L1C1

f = 1/ 2π √58.6 × 10−6 x300 × 10−12 Hz

1199 × 103 Hz

= 1199 kHz

Thus, this is all about Tuned collector oscillator circuit working and applications. We hope that you have got a better understanding of this concept. Furthermore, any doubts regarding this concept or to implement the electrical and electronics projects, please give your valuable suggestions by commenting in the comment section below.Here is a question for you, what is the main function of an oscillator?

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OSCILLATORS Questions with Answers :-

1. An oscillator converts ……………..

  1. c. power into d.c. power
  2. c. power into a.c. power
  3. mechanical power into a.c. power
  4. none of the above
    Answer : 2

2. In an LC transistor oscillator, the active device is ……………

Tuned
  1. LC tank circuit
  2. Biasing circuit
  3. Transistor
  4. None of the above
    Answer : 3

3. In an LC circuit, when the capacitor is maximum, the inductor energy is ……….

  1. Minimum
  2. Maximum
  3. Half-way between maximum and minimum
  4. None of the above
    Answer : 1

4. In an LC oscillator, the frequency of oscillator is ……………. L or C.

  1. Proportional to square of
  2. Directly proportional to
  3. Independent of the values of
  4. Inversely proportional to square root of
    Answer : 4

5. An oscillator produces……………. oscillations

  1. Damped
  2. Undamped
  3. Modulated
  4. None of the above
    Answer : 2

6. An oscillator employs ……………… feedback

  1. Positive
  2. Negative
  3. Neither positive nor negative
  4. Data insufficient
    Answer : 1

7. An LC oscillator cannot be used to produce ……………….. frequencies

Tuned Oscillators Pdf To Doctor

  1. High
  2. Audio
  3. Very low
  4. Very high
    Answer : 3

8. Hartley oscillator is commonly used in ………………

  1. Radio receivers
  2. Radio transmitters
  3. TV receivers
  4. None of the above
    Answer : 1

9. In a phase shift oscillator, we use …………. RC sections

  1. Two
  2. Three
  3. Four
  4. None of the above
    Answer : 2

10. In a phase shift oscillator, the frequency determining elements are …………

  1. L and C
  2. R, L and C
  3. R and C
  4. None of the above
    Answer : 3

11. A Wien bridge oscillator uses ……………. feedback

  1. Only positive
  2. Only negative
  3. Both positive and negative
  4. None of the above
    Answer : 3

12. The piezoelectric effect in a crystal is ……………

  1. A voltage developed because of mechanical stress
  2. A change in resistance because of temperature
  3. A change in frequency because of temperature
  4. None of the above
    Answer : 1

13. If the crystal frequency changes with temperature, we say that crystal has ………….. temperature coefficient

Tuned Oscillators Pdf To Document

  1. Positive
  2. Zero
  3. Negative
  4. None of the above
    Answer : 1

14. The crystal oscillator frequency is very stable due to ………………. of the crystal

  1. Rigidity
  2. Vibrations
  3. Low Q
  4. High Q
    Answer : 4
Pdf

15. The application where one would most likely find a crystal oscillator is ……………..

  1. Radio receiver
  2. Radio transmitter
  3. AF sweep generator
  4. None of the above
    Answer : 2

16. An oscillator differs from an amplifier because it ………

Tuned oscillators pdf to document

Lc Oscillator Pdf

  1. Has more gain
  2. Requires no input signal
  3. Requires no d.c. supply
  4. Always has the same input
    Answer : 2

17. One condition for oscillation is ………….

  1. A phase shift around the feedback loop of 180o
  2. A gain around the feedback loop of one-third
  3. A phase shift around the feedback loop of 0o
  4. A gain around the feedback loop of less than 1
    Answer : 3

18. A second condition for oscillations is ……………….

  1. A gain of 1 around the feedback loop
  2. No gain around the feedback loop
  3. The attention of the feedback circuit must be one-third
  4. The feedback circuit must be capacitive
    Answer : 1

19. In a certain oscillator Av = 50. The attention of the feedback circuit must be …………

Tuned Oscillators Pdf To Docx

  1. 1
  2. 01
  3. 10
  4. 02
    Answer : 4

Oscillator Circuits Pdf

20. For an oscillator to properly start, the gain around the feedback loop must initially be

  1. 1
  2. Greater than 1
  3. Less than 1
  4. Equal to attenuation of feedback circuit
    Answer : 2

21. In a Wien-bridge oscillator, if the resistances in the positive feedback circuit are decreased, the frequency……….

  1. Remains the same
  2. Decreases
  3. Increases
  4. Insufficient data
    Answer : 3

22. In Colpitt’s oscillator, feedback is obtained …………….

  1. By magnetic induction
  2. By a tickler coil
  3. From the centre of split capacitors
  4. None of the above
    Answer : 3

23. The Q of the crystal is of the order of …………

  1. 100
  2. 1000
  3. 50
  4. More than 10,000
    Answer : 4

24. Quartz crystal is most commonly used in crystal oscillators because ………….

  1. It has superior electrical properties
  2. It is easily available
  3. It is quite inexpensive
  4. None of the above
    Answer : 1

27. ………….. is a fixed frequency oscillator

  1. Phase-shift oscillator
  2. Hartely-oscillator
  3. Colpitt’s oscillator
  4. Crystal oscillator
    Answer : 4

28. In an LC oscillator, if the value of L is increased four times, the frequency of oscillations is …………

  1. Increased 2 times
  2. Decreased 4 times
  3. Increased 4 times
  4. Decreased 2 times
    Answer : 4

29. An important limitation of a crystal oscillator is ……………

  1. Its low output
  2. Its high Q
  3. Less availability of quartz crystal
  4. Its high output
    Answer : 1

30. The signal generator generally used in the laboratories is ………….. oscillator

  1. Wien-bridge
  2. Hartely
  3. Crystal
  4. Phase shift
    Answer : 1

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