Oscillators
A parallel combination of an induction coil and a capacitor is called a tank circuit, or LC circuit, which produces the oscillations, and the frequency of these oscillations depends upon the inductance and capacitance of the coil and the capacitor used in the tank circuit.
Oscillators are electronic devices that produce electric oscillations of the desired frequency and amplitude without requiring any external input signal. In other words, it converts DC from the source of the power supply to AC output.
The block diagram of the oscillators is shown in Figure 9.2.24. Obviously, the oscillators may be considered self-sustaining transistor amplifiers with positive feedback.
Principal Sections of the Oscillator Circuit:
As shown in the block diagram of the oscillators in Figure 9.2.24, there are three principal sections:
Tank circuit:
It consists of a capacitor with capacitance C and an induction coil with inductance L combined in parallel. Once provided, the electric energy alternates between magnetic and electrostatic energy in the inductor and capacitor. Thus, LC circuits are where the electrical oscillations are generated. According to this, the tank circuit’s electric oscillation frequency is determined by
The oscillations get damped and die out slowly with the passage of time due to the resistive losses in the inductance coil and the dielectric losses in the capacitor.
Transistor amplifier:
The transistor amplifier receives the oscillations produced by the tank circuit. The transistor’s amplifying operation causes the oscillations to be magnified.
Feedback circuits:
The feedback circuit sends a portion of the transistor amplifier’s output power back to the tank circuit in phase with the input signal to make up for the energy losses that occur in the tank circuit. Positive feedback is the process that causes the sustained, undamped oscillations that are the result of it. On the other hand, negative feedback occurs when a portion of the output is supplied back out of phase with the input signal. Diagram 9.2.24 demonstrates the block diagram of a feedback amplifier where the input receives positive feedback. The amplifier with positive feedback has an overall gain of
With negative feedback, the overall gain of the amplifier is also affected.
Where β is the feedback factor. A is the voltage gain without feedback. Aβ is called loop gain. If Aβ = 1, then for positive feedback, Af = infinite. Therefore, the gain becomes infinite. This shows that there is an output without any inputs. It means the output of the oscillators is self-sustaining. In this condition, the amplifiers become oscillators.
The condition A B = 1 is known as the Barkhausen Criterion for oscillations.
Transistor as an oscillator:
A simple LC circuit can be used to produce electric resolution at a desired frequency. The radiowaves that are used as carrier waves in radio communication are produced using these circuits.
Figure 9.2.25 displays a circuit diagram for a transistor acting as an oscillator. The input, or emitter-base circuit in this case, is forward biased, and a tank circuit made up of an inductance coil with inductance L and a variable capacitor c is attached. The output or collector-emitter circuits that receive reverse bias are coupled to a coil L*, referred to as a tickler coil or a feedback coil. L and L* are inductively connected coils.
Working:
The coil L* experiences a very modest collector current when the taping key (K) is depressed. Due to the fact that coils L and L* are inductively connected, a tiny voltage is induced in coil L as a result of the change in current and subsequent change in magnetic flux through coil L*. The emitter-based circuits receive a little current that is generated due to this low voltage. If the emitter becomes forward-biased as a result of the induced voltage created, the small emitter current results in a comparable rise in the collector current.
When the collector current rises, the increasing magnetic flux linked to the coil L* increases the induced voltage across the coil L, which in turn will further increase the forward bias of the emitter. This increases the emitter current and hence the collector current, which increases still further in this way. In this way, the collector current through the coil L* goes on increasing until the induced emf across the coil L reaches a saturation value.
The magnetic flux also ceases to change as the current hits saturation and stops changing. The induced voltage in coil L, which had been maintaining the emitter current, starts to fall, which also lowers the collector current. As the collector current via coil L* declines, a reverse-directed voltage is produced in the coil, further reducing the emitter current. The collector current is further reduced as a result of this. In the absence of an emitter current, the collector current is carried below its typical value due to the inertia of the collapsing flux.
The magnet flux also stops fluctuating as the current decreases to a minimum and eventually stops. When induced voltage is absent, the collector current begins to rise to its usual level once more, forcing the induced emitter current to rise once more. With the feedback energy reaching the LC circuit at the right phase, this initiates the next cycle, which is then repeated to produce oscillations with a constant amplitude. The frequency of the oscillations the equation causes, as previously stated, The frequency can be varied by changing the capacitance of the valuable capacitor.
Applications of Transistor Oscillators:
Electronic circuits called transistor oscillators produce continuous waveforms, usually in the shape of sinusoidal, square, or triangular waves. As they can produce stable and controllable oscillations, they are used in a wide range of industries. Following are a few typical uses for transistor oscillators:
Signal Generation: Signal generators—devices that produce various sorts of waveforms for testing and monitoring purposes in electronics laboratories—often employ transistor oscillators.
Radio Frequency (RF) Communication: They are essential in RF circuits for modulating and demodulating signals in radio frequency (RF) communication. The carrier wave for information transmission in AM (Amplitude Modulation), FM (Frequency Modulation), and other modulation methods is produced by oscillators.
Creating Clock Signals: Oscillators are used in digital electronics to create clock signals that synchronize the operation of different system components, including microprocessors, microcontrollers, and digital logic circuits.
Local Oscillators in Receivers: They are used in radio receivers to generate the intermediate frequency (IF) signal that is mixed with the incoming RF signal for demodulation.
Frequency Synthesis: It’s required to produce frequencies in many applications that aren’t easily accessible from a crystal oscillator or other sources. Phase-locked loops (PLLs) and voltage-controlled oscillators (VCOs) are used in conjunction with frequency synthesizers to produce a wide range of frequencies.
Oscillator Circuits for Sensors: They are used in many different types of sensors, including ultrasonic sensors, which measure the time it takes for an ultrasonic signal to bounce back in order to determine distance.
Amplifier and Mixer Stages: In RF circuits, oscillators are employed at both the amplification and mixing stages. They can be used to integrate signals of various frequencies in mixing while also amplifying weak signals in amplification.
Frequency Modulation (FM) and Phase Modulation (PM): In FM and PM systems, oscillators are essential because they provide the carrier wave that carries the modulated signal.
Test Equipment Calibration: To produce accurate and consistent reference signals for testing and calibrating other electronic instruments, oscillators are utilized in calibration equipment.
Audio Applications: They produce various musical tones and frequencies in audio synthesizers. They are also used in audio amplifiers to manage the output stage’s biasing.
Voltage-Controlled Oscillators (VCOs): An input voltage can alter the frequency of a particular type of oscillator called a VCO. They are frequently utilized in FM radios, frequency synthesizers, and phase-locked loops (PLLs).
Clock Recovery: In communication systems, oscillators are used for clock recovery in situations where the received signal is asynchronous and needs to be synchronized with the local clock.
These are only a few of the numerous uses for transistor oscillators. However, due to their flexibility and controllability, they are the most common components of modern electronics employed in a range of industries and technologies.
Search
qpmhdsgn http://www.g225816y98omad6xw96uadz9l960jqa7s.org/
aqpmhdsgn
[url=http://www.g225816y98omad6xw96uadz9l960jqa7s.org/]uqpmhdsgn[/url]