Mosfets Biasing Enhanced-Type Mosfets?

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SUMMARY

Enhanced-Type MOSFETs do not utilize a fixed bias configuration due to the unpredictable turn-on voltage and significant temperature drift. Instead, it is essential to implement source resistor degeneration to stabilize the current. The discussion highlights the impact of temperature on propagation delay in CMOS logic circuits, emphasizing the necessity for careful design considerations, particularly in critical timing applications.

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  • Understanding of Enhanced-Type MOSFET characteristics
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Simple Question: Do Enhanced-Type Mosfets (And not Depletion Type ones) have Fixed Bias Configuration? If yes how do we draw the transfer curve? And locate Q point?
(I didnt seem to find it in the book, only present for Depletion types)
 
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It is not advisable to use a fixed voltage to bias an Enhancement MOSFET. The turn on voltage is very unpredictable, it can vary a lot between parts. Also temp. drift is very large. You have to use source resistor degeneration to stabilize the current.

Case in point, propagation delay in CMOS logics change quite a bit with temperature. This is because the switching threshold drift with temperature and the propagation delay change because of the rise time of the driving output. I had to design the critical timing circuits with bipolar logics.
 
Thanks yungman, that's what I foresaw.
 

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