triode 、 FET and MOS tube

Based on the working principle of diode , This article continues to explain and PN The working principle of three kinds of transistors closely related to the junction .

List of articles

• triode 、 FET and MOS tube
• • @[TOC]( List of articles )
• One 、 Working principle of triode
• • 1. Triode conduction
  • 2. Current amplification
• Two 、 Field effect tube （JFET） working principle
• 3、 ... and 、MOS How the tube works

One 、 Working principle of triode

We know that the triode is Current amplifier .
The triode is divided into NPN The type and PNP Type semiconductor , The structure and working principle of the two are basically the same , This article takes NPN The working principle of the transistor is analyzed .

The structure diagram of triode is shown in the figure , There are two inside the tertiary tube PN junction , They are collector junction and emitter junction , Basic set （B）、 Collector （C） And the emitter （E） Three pins .

Apply voltage to the three pins of the triode , What conditions can be reached to make the triode turn on ？
If U2=0, namely B Pole current is 0, The triode must not be on , Because of existence PN The phenomenon of reverse junction bias .

1. Triode conduction

If B Polar current is not 0, How will the three-level linkage work ？ As shown in the figure ：

U2 Greater than a certain value （ It's usually 0.7V）, Then the emission junction is positively biased , The base injects a small current , Will attract electrons from the emitter to the collector , Triode conduction .

2. Current amplification

There are different doping concentrations in the three regions of the triode device , The concentration of the emitter is much higher than that of the base , At this time, a large number of electrons from the transmitter flow to the collector , Thus amplifying the base current .—— The triode works in the linear amplification region

The doping concentration of the three regions is ： The emitter > The base > Collector .

When the base current is greater than a certain value ,** The triode works in the saturated region .** We can use faucet analogy in life , Turn the faucet to the maximum , The water flow reaches the threshold .

Two 、 Field effect tube （JFET） working principle

The three pins of the FET are the gate 、 Source and drain . FET is divided into N Channel and P Channel field effect tube , As shown in the figure below ,

GFET The internal structure of the is as follows

This article takes N Explain the working principle of channel fet , According to its internal structure diagram, there are also two... Inside the FET PN junction , control PN The size of polar inversion layer can be controlled N The channel size controls the current size .

As shown in the figure , The field effect transistor turns on , If the voltage between the grid and the source set is 0 when , The source collector goes to the drain , At this time, the current between the drain and the source is the maximum .
When VGS The pressure difference between is greater than a certain value , Put it in N In the channel fet, the gate voltage is a certain value lower than the source voltage , Then there is no through electric field between FET , So that there is no current between the drain and the source . As shown in the figure below ：

Therefore, the gate can control the on-off of the FET , The control of drain voltage for channel is bidirectional control , The channel cannot be clamped ,VDS If it is greater than a certain value, the channel will reach an equilibrium point , Enter the constant current zone .

3、 ... and 、MOS How the tube works

MOS Tube is FET One of the , Now it mainly uses enhanced MOS tube , It is divided into PMOS and NMOS, Its electrical expression is as follows .
MOS The tube also has a grid （G）、 Drain electrode （D） Heyuanji （S）.
NMOS:

PMOS:

This article takes NMOS Take tube as an example to explain MOS How the tube works , As shown in the figure below , The grid is SIO2.

1. If the grid and source voltages are the same , Apply voltage between drain and source , There is always one PN The knot is reversed , therefore MOS The tube doesn't work .

2. If VGS> Threshold voltage （ Such as 0.7）, At the gate SIO2 An electric field will form inside , So as to attract P Electrons in the substrate repel holes , stay N The poles form a reverse hierarchy , That is, the conduction channel .
Half of the grid voltage is in the insulating layer , Half in the depletion layer , So the grid voltage should reach PN Twice the junction on voltage requirement .
Such as depletion layer requirements 0.7V, To make PN The knot is positive and partial , At this time, the grid voltage must be greater than 1.4V.

Within this stage ,VGS increase , The channel will widen , electric current ID It will increase .

3. When VGS>VT when , electric current ID There will be a threshold , Will follow VDS To increase by ,ID When the threshold is reached , Then enter the constant current area .

See... For the working principle of diode ：https://blog.csdn.net/m0_51390088/article/details/124321747?spm=1001.2014.3001.5502