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Flashcards in FET Deck (11)
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1

How to tell FET drain from source

drain is at positive voltage relative to source by convention

2

What is FET cutoff

Vgs=0, DS is back to back diodes

3

What is enhancement mode FET

normally off, need to control Vgs to turn on

4

What is depletion mode FET

normally on, need to control Vgs to turn off. used as loads in NMOS only process in old CPUs, Motorola 6800 and 6502

5

Describe NMOS

N-type source and drain. P-type substrate. The channel is created by inverting the p-type substrate to n-type with a value of Vgs that is high enough. The channel is also called an inversion layer.

6

How much charge is in the channel

Q=Cox(WL)Vov

7

How to solve for Ids in MOS

(Q/L)(drift velocity)=(Q/m)(m/s)=Q/s=A=(CWVov)(u*Vds/L) -> Ids = u*C*(W/L)(Vov)(Vds) w/o pinch off

Note: Cox = how much charge. un=how fast

8

Regions of MOS operation

Off: Vgs < Vt
Triode: VdsVov Id=f(Vov) a.k.a. pinch off

9

How to make PMOS in p-type subtrate?

Need an n-well

10

Best bias for linear NMOS

Saturate so it's a VCCS with one input.
1) Vgs>Vt,
2) Vds>Vov,
3) Vgd

11

Best bias for linear BJT NPN

NPN in active mode (BC reverse biased)
1) Vbe(on)
2) Vbc < 0.4V
3) Vce > 0.3V