Markings on transistors are often hard to read. Suppose that a student accidenta
ID: 2249444 • Letter: M
Question
Markings on transistors are often hard to read. Suppose that a student accidentally usesa p-channel device in a circuit where an n-channel device is expected. What will happen? Will the device survive? Under what circumstances? Be very specific in your assumptions. (You could assume the student is using any of the circuits from the examples, exercises, lab experiments, or problems in the chapter on MOSFETs.) Feel free to be creative, but be realistic, too. The point of this problem is to give you an opportunity to show your understanding of MOSFET operation. ShineExplanation / Answer
The fundamental difference between a NMOS and PMOS transistors is its switching characteristics.
In PMOS, source and body terminal is tied together to highest voltage i.e. VDD where as in NMOS source and body terminals are tied to lowest potential i.e. GND. Else body bias effect is going to come into picture.
Turning ON a NMOS device is different than what PMOS device is. A positive voltage of minimum threshold voltage (Vth) will be required to turn ON a NMOS where as a negative voltage of magnitude Vth is needed to turn ON PMOS device.
From the saturation characteristics we know that NMOS is a good pull down device (pulling drain voltage to ground) but poor pull up device. Exactly opposite behaivior is exhibited by PMOS device. Hence maximum voltage a NMOS can pass is VDD - Vth and minimum a PMOS can pass is Vth.
Infact above mentioned characteristics is exploited in CMOS designs and they are till date widely in use if we ignore recent nanoscale devices using FINFETs.
Now the question that device survives or not. Answer is typically any mixup will not blow up the device but definately the characteristic will cause wrong operation and erroreneous results.