Difference Between N Channel and P Channel MOSFETs
Comparison of N Channel and P Channel MOSFETs
- The P-channel enhancement MOSFETs were very popular, because it was much easier and cheaper to produce than the N channel device.
But now a days these difficulties have overcome and mass production of N-channel MOSFETs becomes easier.
Thus the N-MOSFETS have replaced PMOSs and P-MOSFETs have almost become obsolete.
- The hole mobility is nearly 2.5 times lower than the electron mobility.
Thus a P channel MOSFET occupies a larger area than the N channel MOSFET having the same ID rating.
At normal fields, in silicon,
the hole mobility is 500 cm2/v.sec
the electron mobility is 1300 cm2/v.sec.
Therefore the P-channel ON resistance will be twice that of n-channel MOSFET ON resistance.
- ON resistance means the resistance of the device when ID is maximum for a given VDS. Its value depends upon μ of carriers.
- P-channel device have holes as majority carriers.
- N-channel device have electrons as majority carriers.
- At the same values of ID and VDS, if the ON resistance of P channel device were to be reduced/make equal to that of N-channel device, then the P-channel device must have more than twice the are of N-channel device. Thus the n -channel devices will be smaller is size.
In other words the packing density of N-channel devices is more (R = ρ. l/ A)
- N channel MOSFETs are fast switching devices. The operating speed is limited by RC time constant of the device. The capacitance is proportional to the junction cross sections.
- The N channel MOSFETs are TTL compatible. As the applied gate voltage and drain supply are positive for an n-channel enhancement MOSFET.
- The drain resistance of P channel MOSFET is 3 times higher than that for an identical N-channel MOSFET.
- The N-Channel MOSFET has the higher packing density which makes it faster in switching applications due to the smaller junction areas and lower inherent capacitance.
- The N-channel MOSFET is smaller for the same complexity than P-channel device.
- Due to the positively charged contaminants, the N-channel MOSFET may turn ON prematurely, whereas the P-channel device will not be affected.
The summary of Difference Between N Channel and P Channel MOSFETs are listed in the following table.
|N-Channel MOSFET||P-Channel MOSFET|
|Have higher packing density, leads to small size||Comparatively low packing density.|
|Smaller in size for same complexity||Size will be more.|
|High switching device. (mobility of electrons is high)||Low switching speed. (mobility of holes is low)|
|Low ON resistance||High ON resistance.|
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