The length of the pendulum is the main thing that controls the frequency. For something to oscillate, energy needs to move back and forth between two forms. For example, in a pendulum, energy moves between potential energy and kinetic energy. When the pendulum is at one end of its travel, its energy is all potential energy and it is ready to fall.
When the pendulum is in the middle of its cycle, all of its potential energy turns into kinetic energy and the pendulum is moving as fast as it can. As the pendulum moves toward the other end of its swing, all the kinetic energy turns back into potential energy. This movement of energy between the two forms is what causes the oscillation. Eventually, any physical oscillator stops moving because of friction.
To keep it going, you have to add a little bit of energy on each cycle. In a pendulum clock, the energy that keeps the pendulum moving comes from the spring. The pendulum gets a little push on each stroke to make up for the energy it loses to friction. See How Pendulum Clocks Work for details. Energy needs to move back and forth from one form to another for an oscillator to work. The other configuration of RC oscillator is the operational amplifier phase lag oscillator.
LC or Inductor-Capacitor Oscillator is a type of oscillator which utilizes a tank circuit to produce positive feedback for sustaining oscillation. The schematic contains an inductor, capacitor, and also an amplifying component. The tank circuit is a capacitor and inductor connected in parallel, the diagram above also includes the switch and voltage source for ease of demonstration of the working principle when the switch is connecting the capacitor to the voltage supply, the capacitor charges.
When the switch connects the capacitor and inductor , the capacitor discharges through the inductor. The increasing current through the inductor starts to store energy by inducing an electromagnetic field around the coil. When the switch connects the capacitor and inductor, the capacitor discharges through the inductor. After discharging the capacitor, the energy from it has transferred into the inductor as an electromagnetic field.
As the energy flow from the capacity decreases, current flow through the inductor decreases - this causes the inductor's electromagnetic field to fall as well. This back EMF then begins to charge the capacitor. Once the capacitor has absorbed the energy from the inductor's magnetic field, the energy is stored once again as an electrostatic field within the capacitor. If we had an ideal inductor and capacitor, this circuit could generate the oscillations forever.
However, a capacitor has current leakage, and inductors have resistance. In real life, however, the oscillations would look as below, as energy is lost.
This loss is called damping. If we want to sustain the oscillations, we need to compensate for the loss of energy from the tank circuit through the addition of active components to the circuit, such as bipolar junction transistors, field-effect transistors, or operational amplifiers. The primary function of the active components is to add the necessary gain, help generate positive feedback, and to compensate for the loss of energy.
The tuned collector oscillator is a transformer and a capacitor connected in parallel and switched with a transistor. This circuit is the most basic LC oscillator schematic. The primary coil of the transformer and capacitor forms the tank circuit, with the secondary coil providing positive feedback, which returns some of the energy produced by the tank circuit to the base of the transistor. This circuit consists of two capacitors in series, forming a voltage divider , which provides feedback to the transistor, with an inductor in parallel.
While this oscillator is relatively stable, it can be hard to tune and is often implemented with an emitter follower circuit so as not to load the resonant network.
To overcome the difficulties tuning the Colpitts oscillator to a specific frequency in production, a variable capacitor in series with the inductor is often added, forming a Clapp Oscillator. This modification allows the circuit to be tuned during production and servicing to the specific frequency required. Unfortunately, this type of LC oscillator is still quite sensitive to temperature fluctuations and parasitic capacitances.
Piezoelectric ceramic material with two or more metal electrodes typically 3 forms the basis of a ceramic resonator. In an electronic circuit, the piezoelectric element resonates mechanically, which generates an oscillating signal of a specific frequency - like a tuning fork.
Ceramic resonators are low cost; however, the frequency tolerance of ceramic resonators is only about - ppm. This tolerance of 0. With frequencies from below 1kHz to beyond 1GHz, there is a range of different materials and vibration modes that ceramic resonators use.
It can be essential to understand the method of resonance used in a device you are placing into your design. Environmental factors such as vibration and shock could impact the function of the resonator within your circuit. The Quartz oscillator is the most common type of crystal oscillator on the market.
Where accuracy and stability are critical, the primary choice is crystal oscillators and their variants. A crystal oscillator stability is measured in ppm parts per million , and stability could be somewhere around 0. An RC oscillator's stability can at best be 0. A quartz crystal can oscillate with very little power required to keep it activated compared to many other oscillators, making them perfect for low power applications.
When the crystal is shock excited by either a physical compression or, in our case, an applied voltage, it will vibrate mechanically at a specific frequency. This vibration will continue for some time, generating an ac voltage between its terminals. This behaviour is the piezoelectric effect, the same as a ceramic resonator.
By comparison to an LC circuit, the crystal's oscillation after the initial excitation will last longer — a result of the crystal's naturally high Q value. For a high-quality quartz crystal, a Q of , is not uncommon. LC circuits typically have a Q of around a few hundred. However, even with the much higher Q, they cannot resonate forever.
There are losses from the mechanical vibration, so it needs an amplifying circuit like RC and LC oscillators. For most devices that will take an external crystal clock source, this will be integrated into the device, and the only additional components required are the load capacitors. The load capacitors are essential; if the capacitance of these is incorrect, the oscillator will not be stable. Typically, the datasheet for the oscillator will contain suggested values, or provide an equation to calculate the correct value for your circuit.
There are many variants of the crystal oscillator; however, beyond a typical crystal, or "XO" you will typically only use the other options for specialised applications. These specialised oscillators can be very expensive and have astonishingly stable and precise oscillations in incredibly challenging environments where absolute precision is required.
While it is certainly possible to construct such circuits, most practical circuits will only have one frequency where such behavior will occur. Often, sine waves are the desired output, for example in a radio system where we want to only transmit on a specified frequency band. We actually have to work hard to design an oscillator that produces a pure sine wave output. Generally, by fourier analysis, any repetitive signal can be seen as a sum of harmonically related sine waves. If it oscillates, I would still consider it an oscillator.
Specifically, the op-amp circuit you're probably thinking of is a form of relaxation oscillator. Wikipedia even uses a diagram of an op-amp oscillator as the first illustration on their page on Electronic Oscillators. Edit In reply to your comment, harmonic content is the content at frequencies that are harmonics multiples of the fundamental operating frequency.
For example, from a 1 kHz oscillator you will get output at 1 kHz, 2 kHz, 3 kHz, etc. The oscillator doesn't filter it out, but you can add a filter at the output of your oscillator to try to filter it out.
If you want a sine wave output, you design the oscillator carefully to generate as little harmonic content as possible. But in general, no matter how careful you are, there will be some harmonics in the output.
They don't die out over time, they are part of the output as long as the oscillator runs. Supercat's answer explains some of the reasons why harmonic distortion in the output is unavoidable. Harmonic content is often undesirable, so you try to design your oscillator to not produce it, but there are no perfect components, so you are always stuck with some harmonic distortion in the output. Theoretically, RC and Wien bridge oscillators generate a single output frequency at a determinable precise point in the spectrum.
This precise point in the spectrum will yield a feedback signal that is either:. At other frequencies the phase shift will be different and will not sustain oscillation. A sinewave is a single point in the spectrum therefore a sinewave is produced by these types of oscillator.
Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? The oscillators consisting of feedback network to satisfy the required conditions of the oscillations are called as feedback oscillators.
Whereas the oscillators with absence of feedback network are called as non-feedback type of oscillators. The UJT relaxation oscillator is the example of non-feedback oscillator which uses a negative resistance region of the characteristics of the device. In oscillators, the frequency of oscillations remains constant over a long interval of time. Frequency stability is a measure of the degree to which the desired frequency is achieved. The closure will be the output to a constant frequency if the frequency stability is better.
The oscillation frequency depends on various features of the circuit such as various components, supply voltages, stray elements, characteristic parameters of active devices, etc. Frequency instability or variations of the desired output frequency may be caused by variations in the external circuit elements or by device characteristics. In transistor oscillators such as a Hartley oscillator or Colpitts oscillators , the frequency of oscillations is not stable during long time operation.
This is because the capacitance existing at the base-collector junction in reverse biased condition is dominated at high frequencies and hence it affects the capacitor in tank circuit. Also, due to change in temperature, the values of frequency dominating components like transistor, inductor, resistor, and capacitor also changes.
Where wr and Tr are the desired frequency and the operating temperature respectively. The frequency stability can be improved by enclosing the oscillator circuit in a constant temperature chamber and by using zener diodes in the circuit to maintain the constant voltage.
A loading effect is reduced by coupling the oscillator circuit to the load loosely, or with the use of a circuit having a low output impedance and a high input impedance. The amplitude stability measures the amount by which the actual output amplitude varies from desired output amplitude in an oscillator. With the increase in the gain of the amplifier, the amplitude of the waveform is change. The gain value is also changes due to the oscillator circuit components, and hence the amplitude.
To keep the gain constant, various gain control techniques are used so that amplitude stability is maintained. Another factor for variation of the amplitude is the supply voltage. The amplitude of the waveform changes with change in the supply voltage. For maintain the good amplitude stability, voltage regulators are used. The stability of the oscillator includes both amplitude and frequency stabilities which depends on various factors.
By considering the above discussed points in the listed form, we get following factors. In case of transistorized oscillators, the changes in the device or transistor parameters which are varied depends on the operation on non-linear portion affect the stability of oscillator. Since the transistor is selected in such way that it operate in linear region of its characteristics.
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