Enhancement vs depletion mode MOSFETs — Hinglish notes

2.4.9 · Hardware › Transistors: BJT & FET

Hum baat kar kya rahe hain?

Naam hi aapko action batata hai:

Enhancement = aap carriers add karte ho conduct karwane ke liye.
Depletion = aap carriers remove karte ho rokne ke liye.

Channel kyun banta hai (ya nahi banta)? — first principles se

Ek n-channel MOSFET lo (source & drain n+ regions hain p-type body mein).

Field kaise kaam karta hai:

Gate, p-type body ke upar oxide par baith ta hai.
Ek positive $V_{GS}$ apply karo. Gate positively charged ho jaata hai.
Yeh field holes ko (p-body mein majority carriers) surface se repel karta hai aur electrons ko surface ki taraf attract karta hai.
Jab kaafi electrons ikatte hote hain, ek patli n-type inversion layer source ko drain se connect karti hai — ek conducting channel banta hai.

Asli fark:

	Enhancement n-MOS	Depletion n-MOS
$V_{GS} = 0$ par channel	koi nahi	pre-doped, exist karta hai
$V_{t h}$ ka sign (n-type)	positive	negative
ON karne ke liye	$V_{GS} > V_{t h}$	already ON hai
OFF karne ke liye	$V_{GS} \leq V_{t h}$	$V_{GS} < V_{t h}$ (negative)
Default state	OFF	ON

P-channel versions ke liye, har sign ulta kar do: enhancement p-MOS ka $V_{t h} < 0$ hota hai (negative gate se ON hota hai), depletion p-MOS ka $V_{t h} > 0$ hota hai.

Figure — Enhancement vs depletion mode MOSFETs

$V_{t h}$ kahan baithta hai — transfer curve

Dono modes saturation mein same drain current equation follow karte hain; sirf $V_{t h}$ shift hota hai.

Squared kyun? $(V_{GS} - V_{t h})$ ka ek factor kitne carriers hain (charge) se aata hai, doosra kitni tezi se push ho rahe hain (field) se. Dono effects linearly scale karte hain → product quadratic hota hai.

Is curve par modes ko distinguish karne wali sirf ek cheez yeh hai ki $V_{t h}$ kahan land karta hai:

E-mode n-MOS: curve ek positive $V_{t h}$ par start hoti hai.
D-mode n-MOS: curve left shift hoti hai, $V_{GS} = 0$ par nonzero $I_{D}$ cross karti hai (iska $V_{t h}$ negative hai).

Common galtiyan (Steel-manned)

Active recall

Recall Jawab padhne se pehle khud test karo

Kya ek enhancement MOSFET normally ON hota hai ya OFF?
Depletion n-MOS ke liye $V_{t h}$ ka sign kya hota hai?
$I_{D}$ ek square law kyun hai, linear kyun nahi?
Depletion n-MOS ko OFF kaise karte hain?

Enhancement MOSFET ka default state (bina gate voltage ke)

OFF — koi channel exist nahi karta jab tak

V_{GS}

V_{t h}

se exceed na kare.

Depletion MOSFET ka default state (bina gate voltage ke)

ON — ek pre-doped channel

V_{GS} = 0

par conduct karta hai.

Depletion-mode n-channel MOSFET ke liye

V_{t h}

ka sign

Negative.

Enhancement-mode n-channel MOSFET ke liye

V_{t h}

ka sign

Positive.

"Enhancement" physically kya matlab hai?

Aap gate se carriers add/attract karte ho ek channel build karne ke liye.

"Depletion" physically kya matlab hai?

Aap gate se carriers remove/repel karte ho existing channel ko khaali karne ke liye.

Saturation drain-current equation

I_{D} = \frac{1}{2} k (V_{GS} - V_{t h})^{2}

for

V_{GS} > V_{t h}

, warna 0.

Drain current overdrive mein quadratic kyun hota hai?

Ek factor channel charge se (carriers ki sankhya), ek field-driven velocity se — dono

(V_{GS} - V_{t h})

mein linear hain.

Kya mode (E/D) aur channel type (n/p) related hain?

Nahi — independent hain; chaaron combinations exist karte hain.

Depletion device ka

I_{D S S}

matlab hai

V_{GS} = 0

par drain current (iska "on" current gate ground hone par).

Recall Feynman: ek 12-saal ke bachche ko samjhao

Socho ek paani ki pipe mein ek squeeze-clamp hai. Enhancement MOSFET mein pipe default se squeeze karke band hai — aapko gate button dabana padta hai isko kholne ke liye aur paani bahane ke liye. Depletion MOSFET mein pipe default se khuli hai — paani pehle se beh raha hai, aur aap gate button dabate ho isko band karne ke liye. Same pipe, same paani ka rule; bas fark yeh hai ki yeh khuli shuru hoti hai ya band.

Connections

MOSFET structure and operation — dono modes ke peeche oxide/inversion physics
Threshold voltage Vth — woh single number jo mode set karta hai
BJT vs MOSFET — voltage-controlled vs current-controlled
CMOS logic — complementary enhancement n- aur p-MOS use karta hai
MOSFET biasing and load lines — jahan transfer curve circuit constraints se milti hai
JFET — inherently depletion-mode hai (compare karo)