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FET technology iis based on the existance of a conducting channel connecting the 2 majority areas. That means for an NMOS that between 2 n+ regions must stand an n-channel. The difference between the 2 options is physially:
Depletion: the channel exists by manufacturing and when we connect the fet to voltage we control its capacitance (and ihe current flow).
Enchacment: the channel does not exit by manufacturing but we make it exist by dragging electrons in its are using the control voltage. As we pass the threshold voltage the current flow starts. The capacitance control is again able using the control voltage.
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For digital electronics most used was (before COMS and rarely today) the enhacment mode since the topology that it offered had better Voltage Transfer Characteristic and lower Power-Delay Product.
For Analog designs you can use the two technologies in the same way.
If you need any further help take a look at:
-Sedra/Smith Microelectronic Circuits (i believe its the best book to help you understand)
-Jeager Microlectronics
-Microelectronics: An integrated Approach - MIT press (offers a second pass on the physics)
There are DE MOSFETs and E MOSFETs. The mode is how you bias them. The bias voltage on a DE MOSFET P channel and N channel are inverse.With a JFET, it's different. You are always reverse biased. So it's only the bias that determines what mode you are in. If you you bias the N channel positive, you are in enhancement. If you bias it negative you are in depletion. Either way, the operation of increasing conductivity or decresing conductivity is the same. I think there is something about 0VGS that is sort of a demarcation between the two modes.
In enhancement mode, a channel has to be induced. Increasing V-GS (voltage b/w gate and source) above the threshold voltage Vt enhances the channel, hence the name enhancement-mode operation and enhancement-type MOSFET. Then applying V-DS (voltage b/w drain and source) causes the drain current to flow.
Depletion-type MOSFET has an implanted channel. Thus if we apply V-DS, the drain current will flow for V-GS = 0
As mentioned in former replies to your question, Depletion and Enhancement Mosfet's differ in the channel formation.
Enhancements Mosfet's have a channel already between the Drain and Source, so adding a gate voltage of either positive or negative polarity, controls its conductivity. This allows us to use a signal of both polarities without having to worry about the MOSFET cutting off
While in Depletiong MOSFET the channel needs to be created, and that is done by adding a DC voltage to the Gate, untill the condition of "Inversion" is reached and the channel is formed. This restricts us to use only signals of one polarity to maintain the MOSFET operating and avoid the cut-off condition.
Do you use both technologies exactly the same way in analog designs or do you have to change a design accordingly to the technology?For instance if you have a schematic with depletion mode mosfet can you used enchantment mode mosfet with the same design?
Because it was referred before in this post it does not seem correct to me...
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