ECE492 Section 3 Notes
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Welcome! Notes for Spring 2022 Electronic Circuits course. Will make this more pretty as things evolve.
My goal is to make Electronic Circuits so easily digestible, you could teach a middle schooler. We'll see if this works.
Hey how are you. I will insert something here later. :)
What is a MOSFET?
- Stands for: Metal Oxide Semiconductor Field Effect Insulator.
See Figure 3a.
Has 3 sides:
- Gate, Drain, and Source
- The gate current is always 0 (Ig = 0).
- It is a symmetrical device (drain as source and vice versa).
- Length of channel is typically 0.03um to 1um
- Width of channel is typically 1um to 100um.
- Gate current is typically 0mA (10^-15mA)
- Drain voltage in position...
Threshold Voltage (Vt)
- At which a sufficient number of mobile electrons accumulate in the channel region to form a conducting channel.
Effective Voltage (or Overdrive Voltage)
- Vov = Vgs - Vt
Additional formulas to consider:
- Kn' = UnCox = Process Transconductance Parameter
- Un = Electron mobility
- Cox = Oxide capacitance
- Kn = MOSFET transconductance parameter = Kn'[w/L]
- r_DS = Channel Resistance = [1/g_DS] = [1/[UnCox][w/L][Vgs-Vt]]
- At V_DS, the channel is going to be deepest at the source and shallower at the drain.
- Channel resistance is inversely proportional to the gate voltage.
- Channel pinch off:
- The zero depth of the channel at the drain ends because of V_DS = V_GS - V_E
- If V_GS < Vtn then no channel, so transistor is working in cut off region (I_D = 0)
- MOSFET operation
- Tniode region
- Saturation region
Now we'll cover (B) Common Emitter Current gain:
- 50 < B < 200
...and (Alpha) Common Base Current Gain:
It sometimes allow current, and sometimes it doesn't.
We'll take this and plug it into to find x2: