0
1.1kviews
Explain Cascode stage, ssm, $r_o$
written 5.9 years ago by | • modified 2.2 years ago |
Subject: CMOS VLSI Design
Topic: Single Stage Amplifier
Difficulty: Medium
ADD COMMENT
EDIT
1 Answer
written 5.9 years ago by | • modified 2.2 years ago |
Subject: CMOS VLSI Design
Topic: Single Stage Amplifier
Difficulty: Medium
written 5.9 years ago by | • modified 5.9 years ago |
Cascode Stage
$gm_1\,V_1=gm_2\,V_2+gmb\,Vbs$
$\therefore V_{out}=- R_D(gm_1\,V_1)$
$\hspace{1.2cm}=-R_D(gm_1\,V_{in})$
$\therefore A_V=\frac{V_{out}}{V_{in}}=-R_D\,gm_1$
-> Expression for $R_O$
Important advantage of cascade is its high output impedance.
To calculate $R_O$, the cascade stage circuit will be modified as follows.
The above circuit can be viewed as common - source stage with degeneration resistor equal to $r_{o1}$.
$\therefore \, R_O=[1+(gm_2+gmb_2)r_{o2}]r_{o1}+r_{o2}$