The pull up to pull down ratio for an n mos inverter driven by another n mos inverter can be evaluated from:

(A) V_inv = Vt − 

(B) Vinv = 

(C) (Vinv − V_t)² = (−V_td)²

(D) (Vinv − Vt) = (−V_td)²

Choose the correct answer from the options given below:

Concept:

An n mos inverter driven by another n mos inverter circuit is given as:

An nmos inverter has a pull up transistor (Q2) that is n-type MOSFET in depletion mode and has a pull down transistor(Q1) that is n-type MOSFET  in enhancement mode.

both MOSFET will be in saturation when V_in = 0.5 Vdd.

Saturation current equation is given as:

I_D = 

In depletion mode,n type provides depletion current Vgs ≤ 0. for max depletion current Vgs=0 is taken.

In depletion mode ,now current equation is written as :

I_D =  × 

in enhancement mode, current equation is wriiten as:

 Vgs= Vinv

ID = × 

current will be same in depletion mode and enhancement mode so written as:

  ×  =  × 

 ×  =   × 

we know    ( since   )

so rewritten as:​

​ × ​ =  × 

 × Z_pd  =   × Z_pu   

this equation can be written as:

Vinv = Vt −   ​

so A and C are correct.

correct option is 4.​​​