Tuned Oscillators Pdf
Tuned collector oscillator. Tuned collector oscillation is a type of transistor LC oscillator where the tuned circuit (tank) consists of a transformer and a capacitor is connected in the collector circuit of the transistor. Tuned collector oscillator is of course the simplest and the basic type of LC oscillators. The tuned circuit connected at the collector circuit behaves like a purely resistive load at resonance and determines the oscillator frequency.The common applications of tuned collector oscillator are RF oscillator circuits, mixers, frequency demodulators, signal generators etc. The circuit diagram of a conventional tuned collector oscillator is shown in the figure below. Circuit diagram. In the circuit diagram resistor R1 and R2 forms a voltage divider bias for the transistor.
ELG4139: Oscillator Circuits Positive Feedback Amplifiers (Oscillators) LC and Crystal Oscillators JBT; FET; and IC Based Oscillators The Active-Filter-Tuned Oscillator.
Re is the emitter resistor which is meant for thermal stability. It also limits the collector current of the transistor. Ce is the emitter by-pass capacitor. The job of Ce is to by-pass the amplified oscillations. If Ce is not there, the amplified AC oscillations will drop across Re and will add on to the base-emitter voltage (Vbe) of the transistor and this will alter the DC biasing conditions. Capacitor C1 and primary of the transformer L1 forms the tank circuit.
C2 is the by-pass capacitor for resistor R2. Working of the tuned collector oscillator. When the power supply is switched ON, the transistor starts conducting and the capacitor C1 starts charging.
When the capacitor is fully charged, it starts discharging through the primary coil L1. When the capacitor is fully discharged, the energy stored in the capacitor as electrostatic field will be moved to the inductor as electromagnetic field. Now there will be no more voltage across the capacitor to keep the current through the coil starts to collapse. In order to oppose this the coil L1 generates a back emf (by electromagnetic induction) and this back emf charges the capacitor again.
Then capacitor discharges through the coil and the cycle is repeated. This charging and discharging sets up a series of oscillations in the tank circuit. The oscillations produced in the tank circuit is fed back to the base of transistor Q1 by the secondary coil by inductive coupling. The amount of feedback can be adjusted by varying the turns ratio of the transformer.
The winding direction of the secondary coil (L2) is in such a way that the voltage across it will be 180° phase opposite to that of the voltage across primary (L1). Thus the feedback circuit produces a phase shift of 180° and the transistor alone produces a phase shift of another 180°. As a result a total phase shift of 360° is obtained between input and output and it is a very necessary condition for positive feedback and sustained oscillations. The collector current of the transistor compensates the energy lost in the tank circuit.
This is done by taking a small amount of voltage from the tank circuit, amplifying it and applying it back to the tank circuit. Capacitor C1 can be made variable in variable frequency applications. The frequency of oscillations of the tank circuit can be expressed using the following equation: F = 1/2π√(L1C1) Where F is the frequency of oscillation. L1 is the inductance of the transformer primary and C1 is the capacitance.
An electronic oscillator is an that produces a periodic, electronic signal, often a or a. Oscillators convert (DC) from a power supply to an (AC) signal. They are widely used in many electronic devices. Common examples of signals generated by oscillators include signals broadcast by and, clock signals that regulate computers and, and the sounds produced by electronic beepers and. Oscillators are often characterized by the of their output signal:. A (LFO) is an electronic oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio, to distinguish it from an audio frequency oscillator.
Wein Bridge Oscillators Pdf
An audio oscillator produces frequencies in the range, about 16 Hz to 20 kHz. An RF oscillator produces signals in the (RF) range of about 100 kHz to 100 GHz. Oscillators designed to produce a high-power AC output from a DC supply are usually called. There are two main types of electronic oscillator — the linear or harmonic oscillator and the nonlinear. Block diagram of a feedback linear oscillator; an amplifier A with its output v o fed back into its input v f through a, β(jω).
The harmonic, or, oscillator produces a output. There are two types: Feedback oscillator The most common form of linear oscillator is an such as a or connected in a with its output fed back into its input through a frequency selective to provide. When the power supply to the amplifier is first switched on, in the circuit provides a non-zero signal to get oscillations started. The noise travels around the loop and is amplified and until very quickly it converges on a at a single frequency. Feedback oscillator circuits can be classified according to the type of frequency selective filter they use in the feedback loop:. In an circuit, the filter is a network of and. RC oscillators are mostly used to generate lower frequencies, for example in the audio range.
Common types of RC oscillator circuits are the and the. In an LC oscillator circuit, the filter is a (often called a tank circuit; the tuned circuit is a ) consisting of an (L) and (C) connected together. Charge flows back and forth between the capacitor's plates through the inductor, so the tuned circuit can store electrical energy oscillating at its. There are small losses in the tank circuit, but the amplifier compensates for those losses and supplies the power for the output signal. LC oscillators are often used at, when a tunable frequency source is necessary, such as in, tunable radio and the in.
Typical LC oscillator circuits are the, and circuits. Two common LC oscillator circuits, the Hartley and Colpitts oscillators. In a circuit the filter is a crystal (commonly a ). The crystal mechanically vibrates as a, and its frequency of vibration determines the oscillation frequency. Crystals have very high and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators.
Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most, and to generate the in computers and. Crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the; the circuit is also commonly used. Quartz crystals are generally limited to frequencies of 30 MHz or below. Other types of resonator, and (SAW) devices, are used to control higher frequency oscillators, up into the range. For example, SAW oscillators are used to generate the radio signal in.
Negative resistance oscillator. (left) Typical block diagram of a negative resistance oscillator. In some types the negative resistance device is connected in parallel with the resonant circuit. (right) A negative resistance microwave oscillator consisting of a in a. The negative resistance of the diode excites microwave oscillations in the cavity, which radiate out the aperture into a. In addition to the feedback oscillators described above, which use amplifying active elements such as transistors and operational amplifiers, linear oscillators can also be built using (two terminal) devices with, such as tubes, and.
Negative resistance oscillators are usually used at high frequencies in the range and above, since at these frequencies feedback oscillators perform poorly due to excessive phase shift in the feedback path. In negative resistance oscillators, a resonant circuit, such as an, or, is connected across a device with, and a DC bias voltage is applied to supply energy. A resonant circuit by itself is 'almost' an oscillator; it can store energy in the form of electronic oscillations if excited, but because it has electrical resistance and other losses the oscillations are and decay to zero. The negative resistance of the active device cancels the (positive) internal loss resistance in the resonator, in effect creating a resonator with no damping, which generates spontaneous continuous oscillations at its.
The negative resistance oscillator model is not limited to one-port devices like diodes; feedback oscillator circuits with amplifying devices such as transistors and also have negative resistance. At high frequencies, transistors and FETs do not need a feedback loop, but with certain loads applied to one port can become unstable at the other port and show negative resistance due to internal feedback, causing them to oscillate. So high frequency oscillators in general are designed using negative resistance techniques. Some of the many harmonic oscillator circuits are listed below: Active devices used in oscillators and approximate maximum frequencies Device Frequency vacuum tube 1 GHz (BJT) 20 GHz (HBT) 50 GHz (MESFET) 100 GHz, fundamental mode 100 GHz tube 100 GHz (HEMT) 200 GHz tube 200 GHz, harmonic mode 200 GHz diode 300 GHz tube 300 GHz., a.k.a. Meissner oscillator. Cross-coupled oscillator. Relaxation oscillator.
Main article: A nonlinear or produces a non-sinusoidal output, such as a,. It consists of an energy-storing element (a or, more rarely, an ) and a nonlinear switching device (a, or negative resistance element) connected in a. The switching device periodically charges and discharges the energy stored in the storage element thus causing abrupt changes in the output waveform. Square-wave relaxation oscillators are used to provide the for circuits such as timers and, although crystal oscillators are often preferred for their greater stability. Triangle wave or sawtooth oscillators are used in the timebase circuits that generate the horizontal deflection signals for in analogue and sets. They are also used in (VCOs), and, (ADCs), and in to generate square and triangle waves for testing equipment. In general, relaxation oscillators are used at lower frequencies and have poorer frequency stability than linear oscillators.
Are built of a ring of active delay stages. Generally the ring has an odd number of inverting stages, so that there is no single stable state for the internal ring voltages. Instead, a single transition propagates endlessly around the ring. Some of the more common relaxation oscillator circuits are listed below:. Voltage-controlled oscillator (VCO).
Main article: An oscillator can be designed so that the oscillation frequency can be varied over some range by an input voltage or current. These are widely used in, in which the oscillator's frequency can be locked to the frequency of another oscillator. These are ubiquitous in modern communications circuits, used in, and forming the basis of circuits which are used to tune radios and televisions. Radio frequency VCOs are usually made by adding a diode to the or resonator in an oscillator circuit.
Changing the DC voltage across the varactor changes its, which changes the of the tuned circuit. Voltage controlled relaxation oscillators can be constructed by charging and discharging the energy storage capacitor with a voltage controlled. Increasing the input voltage increases the rate of charging the capacitor, decreasing the time between switching events. History The first practical oscillators were based on, which were used for lighting in the 19th century.
The current through an is unstable due to its, and often produces hissing, humming or howling sounds which had been noticed by in 1846, and in 1878. In 1888 showed that the current through an electric arc could be oscillatory. An oscillator was built by in 1892 by placing an in parallel with an electric arc and included a magnetic blowout. Independently, in the same year, realized that if the damping resistance in a resonant circuit could be made zero or negative, the circuit would produce oscillations, and, unsuccessfully, tried to build a negative resistance oscillator with a dynamo, what would now be called a.
The arc oscillator was rediscovered and popularized by in 1900. Duddell, a student at London Technical College, was investigating the hissing arc effect. He attached an (tuned circuit) to the electrodes of an arc lamp, and the negative resistance of the arc excited oscillation in the tuned circuit. Some of the energy was radiated as sound waves by the arc, producing a musical tone.
Duddell demonstrated his oscillator before the London by sequentially connecting different tuned circuits across the arc to play the national anthem '. Duddell's 'singing arc' did not generate frequencies above the audio range.
In 1902 Danish physicists and P. Pederson were able to increase the frequency produced into the radio range by operating the arc in a hydrogen atmosphere with a magnetic field, inventing the, the first continuous wave radio transmitter, which was used through the 1920s. A 120 MHz oscillator from 1938 using a parallel rod resonator.
Transmission lines are widely used for UHF oscillators. The vacuum tube feedback oscillator was invented around 1912, when it was discovered that feedback ('regeneration') in the recently invented could produce oscillations. At least six researchers independently made this discovery, although not all of them can be said to have a role in the invention of the oscillator. In the summer of 1912, observed oscillations in audion circuits and went on to use positive feedback in his invention of the. German independently discovered positive feedback and invented oscillators in March 1913. At General Electric observed feedback in 1913.
Fritz Lowenstein may have preceded the others with a crude oscillator in late 1911. In Britain, H. Round patented amplifying and oscillating circuits in 1913. In August 1912, the inventor of the audion, had also observed oscillations in his amplifiers, but he didn't understand its significance and tried to eliminate it until he read Armstrong's patents in 1914, which he promptly challenged. Armstrong and De Forest fought a protracted legal battle over the rights to the 'regenerative' oscillator circuit which has been called 'the most complicated patent litigation in the history of radio'. De Forest ultimately won before the Supreme Court in 1934 on technical grounds, but most sources regard Armstrong's claim as the stronger one. The first and most widely used relaxation oscillator circuit, the, was invented in 1917 by French engineers Henri Abraham and Eugene Bloch.
They called their cross-coupled, dual vacuum tube circuit a multivibrateur, because the square-wave signal it produced was rich in, compared to the sinusoidal signal of other vacuum tube oscillators. Vacuum tube feedback oscillators became the basis of radio transmission by 1920. However, the vacuum tube oscillator performed poorly above 300 MHz because of interelectrode capacitance.
To reach higher frequencies, new 'transit time' (velocity modulation) vacuum tubes were developed, in which electrons traveled in 'bunches' through the tube. The first of these was the (1920), the first tube to produce power in the range. The most important and widely used were the (R. Varian, 1937) and the cavity (J. Randall and H. Mathematical conditions for feedback oscillations, now called the, were derived by in 1921. The first analysis of a nonlinear electronic oscillator model, the, was done by in 1927.
He showed that the stability of the oscillations in actual oscillators was due to the of the amplifying device. He originated the term 'relaxation oscillation' and was first to distinguish between linear and relaxation oscillators. Further advances in mathematical analysis of oscillation were made by and in the 1930s. Kurokawa derived necessary and sufficient conditions for oscillation in negative resistance circuits, which form the basis of modern microwave oscillator design.
See also. References.