An oscillator uses a feedback circuit (LC) capacitor circuit, a frequency selective RC (resistance capacitor) circuit or a quartz crystal circuit on a feedback path. Generally, the output waveform output from the tuned oscillator circuit is sinusoidal and for this positive feedback it is used around an amplifier device such as a transistor or op amplifier.
If a negative feedback is applied to a gain, the amplifier gains, but the stability increases. With positive feedback, however, it increases profit, but stability shrinks. This increase in profits results in a situation in which an alternating sinusoidal output arrives without input. The amplifier now has become an oscillator that provides an alternating output, and this energy needed to maintain oscillation comes from DC power.
As a frequency defining unit, a parallel-tuned LC circuit or a RC circuit is used, which is "tuned" to oscillate around its resonant frequency, such as a name-tuned oscillator. The output of the device feedbacks to its input so that the feedback signal helps to change the input signal. There is no need for an input signal because the frequency decoding unit provides its own signal through the feedback network such that the circuit is independent. This kind of circuit generally knows the feedback oscillator (positive feedback) and oscillators that use this technique: LC oscillators: The LC oscillators use a parallel tuned inductor condenser tank circuit as a frequency defining unit. The capacitor continuously charges and discharges through the selected resonance frequency, but due to the coil resistance, the dielectric of the capacitor and the heavy losses during the circuit radiation. So in a practical LC circuit, the amplitude of the oscillation voltage decreases every half cycle and these oscillations are always zero. If enough power is supplied at the right time from the DC power supply in the cycle to overcome the losses, the oscillation will stop at constant frequency and amplitude. The resonant frequency occurs when the inductive reactance of the coils (XL) is equal to the capacitance reaction (XC). Oscillations are controlled by varying the value of the condenser (varactor).
- Hartley Oscillator
- Clapp Oscillator
- Colpitts Oscillator
- Tuning Collector Oscillator
- Pierce Oscillator
- phase shift oscillators "as their oscillating elements consist of resistor-capacitor circuits that produce a phase shift circuit corresponding to positive feedback. RC networks are not, of course, oscillating circuits, but become alternating elements when connected transistors or operating amplifiers are used.
RC oscillators do not use inductivity but generate oscillations at a frequency at which the RC network produces 180 °. phase delay. Single-stage amplifier provides 180 degree performance. phase shift between input and output and which can be used to produce the desired positive feedback. The output of the amplifier is fed to the input through the RC network. The input is 180 degrees. on the amplifier and 180 degrees. on the RC network and 180 degrees. + 180 degrees. = 360 degrees. or zero phase shift.
One useful feature of the RC oscillator is that the output frequency is inversely proportional to the capacity, which means that the capacity change produces a much higher frequency than the LC oscillator. However, the disadvantages are that the output power of the RC oscillator is low due to the dissipation in resident elements and if the positive feedback occurs, the amplifier gain should be greater than 29.
Tuned Oscillator Circuits with RC (Resistor / Condenser Phase Shift Circuit Includes:
- Oscillator shift stage
- Oscillator relaxation
- Quadrature oscillator
- Wein bridge oscillator
- Connected condenser oscillator
- Digital oscillators
- Phase retard oscillator (voltage transmission)
Crystal oscillators: Quartz and some other crystalline materials have a "piezoelectric" effect. If mechanical stress or physical deformation is applied to two surfaces of a properly cut crystal, tension between surfaces is obtained. Likewise, when the crystal is stressed, it causes some physical deformation to the current shape of the crystal.
If the tension generated by the mechanical deformation is fed in some way, the mechanism itself distorts the crystal that will cause tension that will last forever. This is the basis for a number of crystal oscillators, as this feedback occurs only with the natural frequency of crystal vibration, and this natural frequency is determined by the "cutting" of the crystal. Then the crystal actually acts as a resonant circuit with very narrow bandwidth.
Stable and frequency limits available from standard LC or RC tuned oscillators. Quartz crystal oscillators operate at very high frequencies up to 10Mhz in parallel mode. They have extremely high stability and resonant frequencies with a very high Q factor, ideal for CPU, microcontroller and video applications. Unlike the above tuning oscillators, the LC feedback loop of the unbalanced oscillator has no LC tank circle, frequency selective RC or crystal circuit. Instead, an uneven oscillator uses nonlinear feedback, and usually an output waveform from a non-contiguous oscillator is not sinusoidal, such as quadrilateral, triangular wave or impulse characterized by a sudden transition from a state of stability or state. Untuned oscillators are generally relaxation oscillators. The oscillators of the untuned oscillators are as follows: Ring Oscillator: Ring Oscillators are composed of "odd" logic gates or amplifiers that are connected in a serial chain so that the last output of the input is the first ring type circuit. Frequency of oscillation depends on the propagation delay of the applied components and the odd "sections" in the ring. The oscillation frequency is very high as the power consumption. Ring oscillators are novel because their high frequencies and the use of parts are practically impractical as oscillators.
Relaxation Oscillators: Relaxation oscillators are mostly multivibrators. These are the groups of oscillators in which the active devices in the circuit (usually a transistor) go beyond the cutting and saturation range for a period of time. Relaxation oscillators are inexpensive and easy to build, as the three main multivibrator types exist.
- Astable Multivibrator: – has no stable status.
- Monostabil Multivibrator: – is in a stable state.
- Bistabil Multivibrator: – There are two stable states.
555 and Scheduling Cards: In addition to the NE555 timing and variations, various favorite chips use both TTL and CMOS to produce various different waveforms and signals, some of which are the most popular: 74LS121, 74LS123, 74LS221 and their variants.