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How does a MOSFET work?

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zahrein

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Can anybody tell mehow mosfet works..I just only know that it is controlled by the voltage input (vgs).

Any explanation or any links that can help me to make me undestand better ?
 

How mosfet works?

The gate-source voltage (vgs) will induce a channel between the drain and the source. The dimension of the channel induced depends on the vgs. The higher the vgs, the larger the channel, thus more current will flow. You may refer to "Analysis and Design of Analog Integrated Circuits" by Gray Meyer.
 

Re: How mosfet works?

To further complicate matters you also have depletion and enhancement type MOSFETS. The one type will have conduction with no potential on the gate while the last type needs a potential before it conducts. They are both available as N or P type devices. Any good search on Google will give the full details of the differences between them.
 

Re: How mosfet works?

a mos transistor has:
weak inversion, saturated
strong inversion, triode and saturated.
and cut.
you can find mor information on Gray's book: Analysis and design of analog integrated circuits
 

Re: How mosfet works?

Look at :
analog integrated circuits (chapter 3) by Gray & Mayer
 

Re: How mosfet works?

Hi,

You may want to refer to the following links for some application notes on MOSFET.



Cheers,
 

Re: How mosfet works?

What I find interesting is the current in P type and N type. The P type has current at the covalent band while N type has current in the conduction band. Could someone elaborate on this. It appears there is an energy difference here.
 

Re: How mosfet works?

what do you mean with "covalent band"¿?
 

Re: How mosfet works?

There is two types of current. Conduction band current which is the higher energy band and covalent current which is the lower energy band. The lower band is what produces hole current. In N type, you have free electrons in the conduction band. In P type, you don't have free eletrons. The current is in the covalent, bonding, energy band. As the electrons flow in the covalent band, they leave holes in their wake. This wake of holes is what's called hole current. So you can have current in two different energy bands.
 

Re: How mosfet works?

I think there is more to it.

MOSFET is a FET. Field Effect Transistor. It is very easy to make Metal Oxide FET transistors that is why they are mostly used for primarly.

Just like any kind of transistor mostly, they are N-type or p-type.
PRIMARLY to notice in MOSFET is that there is NO contact between gate and source or drain.

Here is another trick for what I just said. What is the input impedance? You bet it is. It the most maximum you can reach among other solid-state transistor device. Get your conclusions here as for voltage-driven rather than current-driven(power consumption is minimum).

Get your conclusions what you can make out of this device(and other variations of it).

Operations most of guys above did explain them quite thoroughly.
 

Re: How mosfet works?

There is also a gate current associated with FETs. To say they use less power is something that is debatable. In fact, the power dissipated is the current times VDS as well as the power dissipated by a transistor is the current times VCE.
 

Re: How mosfet works?

Mosfet basic article can answer you question:

**broken link removed**
 

Re: How mosfet works?

Kevin Weddle said:
There is also a gate current associated with FETs. To say they use less power is something that is debatable. In fact, the power dissipated is the current times VDS as well as the power dissipated by a transistor is the current times VCE.
An ideal FET should not have any gate current. A practical one probably has, but way less than that of a transistor. The current used to calculate the power dissipation is the drain/collector current, and NOT the gate current! (Assuming base/gate currents are small compared to drain/collector currents) Normally gate current would be in the order of uA, while base current would be in the range of mA. Power MOSFETs usually dissipate a lot of heat for the simple reason that they usually sustain much higher current loads than power transistors.
 
Re: How mosfet works?

There is a book which was writen by "gray|hurst|Lewis|Meyer" The title is "Analysis and Design of Analog Integrated Circuits", it not only talk about Bipolar, but Mosfet as well. You can get a whole picture of it.
 

How mosfet works?

You can read "Microelectronic Circuits" by Sedra.
 

Re: How mosfet works?

The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), is by far the most common field-effect transistor in both digital and analog circuits. The MOSFET is composed of a channel of n-type or p-type semiconductor material (see article on semiconductor devices), and is accordingly called an NMOSFET or a PMOSFET (also commonly nMOSFET, pMOSFET, NMOS FET, PMOS FET, nMOS FET, pMOS FET).

The 'metal' in the name is an anachronism from early chips in which the gates were metal; modern chips use polysilicon gates. IGFET is a related, more general term meaning insulated-gate field-effect transistor, and is almost synonymous with "MOSFET", though it can refer to FETs with a gate insulator that is not oxide. Some prefer to use "IGFET" when referring to devices with polysilicon gates, but most still call them MOSFETs.

Usually the semiconductor of choice is silicon, but some chip manufacturers, most notably IBM, have begun to use a mixture of silicon and germanium (SiGe) in MOSFET channels. Unfortunately, many semiconductors with better electrical properties than silicon, such as gallium arsenide, do not form good gate oxides and thus are not suitable for MOSFETs.

The gate terminal is a layer of polysilicon (polycrystalline silicon; why polysilicon is used will be explained below) placed over the channel, but separated from the channel by a thin insulating layer of what was traditionally silicon dioxide, but more advanced technologies used silicon oxynitride. When a voltage is applied between the gate and source terminals, the electric field generated penetrates through the oxide and creates a so-called "inversion channel" in the channel underneath. The inversion channel is of the same type — P-type or N-type — as the source and drain, so it provides a conduit through which current can pass. Varying the voltage between the gate and body modulates the conductivity of this layer and makes it possible to control the current flow between drain and source.



300px-MOS_768x576.jpg
 

Re: How mosfet works?

Vgs induces the channel between the source and drain and according to its value the width of the channel is set...and the saturation current value is set

Vds controls the current that actually flows in the channel
 

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