P Channel Enhancement Type Mosfet

difference between Depletion MOSFET vs Enhancement MOSFET

P Channel Mosfet Circuit Examples
P Channel Enhancement Type Mosfet Test

This page on Depletion MOSFET vs Enhancement MOSFET mentions difference between Depletion MOSFET and Enhancement MOSFET.

Depletion MOSFET

The P-channel MOSFETs are simply called as PMOS. The symbols for P-channel MOSFET are as given below. Now, let us go through the constructional details of an N-channel MOSFET. Usually an NChannel MOSFET is considered for explanation as this one is mostly used. Since the conductivity of the channel is enhanced by the positive bias on the gate so this device is also called the enhancement MOSFET or E- MOSFET. The minimum value of gate-to-source voltage V GS that is required to form the inversion layer (N-type) is termed the gate-to-source threshold voltage V GST. For V GS below V GST, the drain current.

Figure-1 depicts construction of depletion type MOSFET. It also mentions circuit symbol of N-channel MOSFET of depletion type.Due to its construction if offers very high input resistance (about 10¹⁰ to 10¹⁵).Significant current flows for given V_DS at V_GS of 0 volt.

When gate(i.e. one plate of capacitor) is made positive, the channel((i.e. the other plate of capacitor) will have positive chargeinduced in it. This will result into depletion of majority carriers(i.e. electrons) and hence reduction inconductivity. Hence the curve similarto JFET is obtained as shown in the figure-2.

P Channel Mosfet Circuit Examples

As shown in the symbol here gate is insulated from the channel.For P-channel type MOSFET symbol, arrow will be reversed.

Figure-2 depicts drain characteristics and transfer curve of depletion type of MOSFET(N-channel).

Enhancement MOSFET

P Channel Enhancement Type MOSFETs. The body of a P-Channel eMOSFET is made by a lightly doped N-type substrate. While the source and drain are heavily doped with P-type impurities. These are the following features of a P-Channel eMOSFET. P-channel has majority-carriers of holes. Enhancement-Type ('Normally OFF') P-Channel MOSFET is like an upside-down N-Channel MOSFET. It starts to conduct if Gate value is sufficiently lower than Source. If you connect the Source of a P-Channel MOSFET to VCC, then you can use a voltage between VCC (+) and Ground (-) to turn it ON and OFF.

Figure-3 depicts construction of enhancement type MOSFET. It also mentions circuit symbol of N-channel MOSFET of enhancement type.Here continuous channel does not exist from source to drain. Hence no current flows at zero gate voltage.Symbol depicts broken channel between 'S' to 'D' terminals.

When positive voltage is applied to the gate, it will induce a channel by flowing minority carriers(i.e. electrons) fromP-type bulk into the concentrated layer.

Drain and transfer characteristics of p channel enhancement type mosfet

Figure-4 depicts drain characteristics and transfer curve of enhancement type of MOSFET(N-channel).As shown in the figure-4 minimum threshold voltage is needed for the flow of drain current to start.

This type of FET is ideal for switching application. This is due to the fact that no gate voltage is needed to keepthe device in 'off' state. Moreover the device can be powered ON with the application of same polarity as drain terminal.

Following are the important comparison features between Depletion and Enhancement MOSFET types:
• Enhancement MOSFET does not conduct at 0 volt, as there is no channel in this type to conduct.Depletion MOSFET conducts at 0 volt. Moreover when positive cut-off gate voltage is applied to depletion MOSFET,hence it is less preferred.
• The depletion MOSFET does not have any kind of leakage currents such as gate oxide and sub threshold type.
• Depletion MOSFET logic operations are opposite to enhancement type of MOSFETs.
• Diffusion current(i.e. sub-threshold leakage current) exists in enhancement MOSFET whiledepletion MOSFET do not have any diffusion current.