Field Transistor On Circuits

When designing circuits, many details play an important role: resistors, transistors, capacitors. At the same time, each of them is divided into certain types. And the article will be considered What is it? What are the field switching transistors? And where are these devices used?

Field effect transistor

field effect transistor circuit

Initially, we define the terminology. A field effect transistor is a semiconductor device through which a stream of charge carriers moves. It is governed by a transverse-type electric field, which, in turn, is created by the voltage that is applied between the drain and the gate or the source and gate. Due to the fact that the principle of operation of field-effect transistors is based on the movement of the main charge carriers of the same type (holes or electrons), they are called unipolar.

In practice, the most commonly used circuit is a transistor with a common emitter. The fact is that using the source in the first place allows to obtain a significant increase in current and power.In this case, when the switching circuit of the common base transistor is used, the current index does not increase. Therefore, the power index increases significantly less than in the case of the emitter. Also, when betting on the base, you must understand that the circuit then has a low input resistance. Therefore, the use of such an approach in the practice of the strong is limited in amplification technology. Well, let's start to consider the inclusion of field-effect transistors.

Common source circuit

transistor circuitThe source is the electrode through which the main charge carriers enter the channel. This is a circuit for switching on a field-effect transistor, in which the control p-n-junction uses this part in general mode.

The scheme with a common drain

transistor power circuitsThe drain is the electrode through which the main charge carriers leave. This is the circuit where the field-effect transistor is turned on, which has a controlling pn-junction and uses this part in general mode.

General shutter circuit

bipolar transistor circuitThe shutter is an electrode that serves to regulate the cross section of the channel. Before you is a circuit where a field-effect transistor is turned on, in which the controlling pn-junction uses this part in general mode.

Types of field effect transistors

When oriented according to the details of electrical circuits, they take into account the following indicators: internal and external resistance, cut-off voltage and the steepness of the drainage characteristics. Field effect transistors are divided into two main types:

  1. Having a pn-junction.
  2. With insulated shutter.

Wiring transistors are the same in both types.

Field-effect transistor with pn-transition

common emitter transistor circuit

A device with a control pn-junction is a field effect transistor, where the plate is made of a semiconductor of the same type and has electrodes (source and drain) at opposite ends. Thanks to them, it is included in the controlled circuit. That, in turn, is connected to the third electrode (which is called the gate) and forms an area in which there is a different type of conductivity. These are the schemes for switching on the transistor. If the plate has the index n, then it will be p. The power source, which is included in the input circuit, implements a reverse voltage on a single junction. Also, the vibration amplifier is connected here. When the input voltage changes, the reverse also changes. Channel conduction is n- and p-type.Depending on it, the polarity of the bias voltage can change to the opposite value. Circuit switching transistor is very dependent on the goal and its characteristics. This type of field-effect transistor is similar in its principle of operation to a vacuum triode, although there are some differences. Also, their important advantage is that they have a low noise level. This is possible due to the fact that the injection of minority carriers is not used. Also from the surface of the semiconductor crystal channel of the field-effect transistor is separated. Circuit switching transistor on this process have no effect.

Field effect transistor having an isolated gate

Device where there is an isolated shutter. A semiconductor crystal with a fairly high resistivity has two heavily doped regions with the opposite type of conductivity. The design feature of this type of field-effect transistor is that the gate is separated by a dielectric layer from the main part of the device. On highly doped areas there are metal electrodes - drain and source.The distance between them can be less than a micron. The surface between the source and drain is covered with a thin layer (about 0.1 micrometer) of the dielectric. Since silicon is used as a conductor, the insulator is its dioxide, which is grown by oxidation at high temperature. A metal electrode is applied to the dielectric layer. This diversity has led to the emergence of a new name - MOSFET. After all, the construction uses metal, dielectric and semiconductor. Although the inclusion of transistors from this does not change.

There are two types of field MOSFET transistors:

  1. Induced channel.Can produce a significant increase in electromagnetic waves, both in power and voltage.
  2. Built-in channel.Can work in 2 modes and change static characteristics.

Field of application of the transistor

common base transistor circuit

CMOS structures that are built from a complementary pair of these devices and which have different types of channels (n- and p-) have found wide application in analog and digital integrated circuits. Due to the fact that field-effect transistors are controlled by the field (more precisely,the size of the voltage that goes to the gate), and not the current that flows through the base (as can be observed in bipolar transistors), there is less energy consumption. This is relevant for tracking and waiting devices, as well as where it is necessary to ensure low power consumption and energy saving (sleep mode on the phone). In contrast to the field circuit, the inclusion of bipolar transistors will require more energy, so you should not count on their long-term operation without a source of constant energy. This is one of the most significant advantages. Inclusion schemes for bipolar transistors, by the way, are based on more familiar to most radio amateurs terms: base, emitter and collector.

As an example of the use of field-effect transistors in practice, you can bring a remote control or a wrist quartz watch. Due to the implementation with the use of CMOS structures, these devices can boast of work in several years, using only one miniature power source, such as a battery or battery. These are the advantages of transistor turn-on circuits.And this is not the limit of their use. Due to constructive improvement, field-effect transistors are increasingly used in various radio devices, where they successfully replace bipolar transistors. Since in the open state they have low resistance, they can be found in amplifiers that increase the sound frequencies of high fidelity. The use of radio transmission technology allows to increase the frequency of the carrier signal and thus provide devices with high noise immunity. Therefore, the switching circuit of the transistor and enjoy such popularity.

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