1

2

3

Low frequency model High frequency model

Cπ is the capacitance of the forward-biased BE junction Cμ is the Capacitance of the reverse-biased BC junction The value of Cμ is usually much smaller than Cπ

typical circuit parameter values of Cμ = 0.02 pF and Cπ = 0.2 pF

4

The common emitter amplifier has a high gain. (advantage)ButIt has limited bandwidth (FH-FL). Its FH is not that large.(disadvantage)

5

The cascode amplifier has a high gain. (advantage)It has higher bandwidth (FH-FL) than that of common emitter amplifier .

Its FH is large.(advantage) Why?!!!!!!!

6

The CE amplifier has only two internal capacitances, the cascode amplifier has four internal capacitances. Since FH is inversely proportional to internal capacitors, CE should have higher FH.

Noooooooooooooo, Why?

7

Also we call this as miller effect. As K increases this will lead C1 to be large

8

Cπ doesn't suffer from miller effect sine it has a Ground terminal

C suffers from miller effect

The values of K about (-100 to -400)

C1 becomes from (100 to 400)C

The high value of C1 makes FH limited

9

Cπ1 , Cπ2 , and Cdoesn't suffer from miller

C suffers from miller effect

C1 and C2 become equal 2C

FH is large

effect because of the Ground terminal

Small values of internal capacitors and small millereffect

smaller miller effect

Both the C.E. and Cascode amplifiers almost have the same Am, Rin, Rout and FL, But

10

C.E.

Cascode

11

Measure:1- AM

2-RIN

(Use RD = 1 kΩ)

3-RO

(Use RD = 1 kΩ)

4-FL

5-FH

ExperimentaExperimentallylly

12

Measure:1- AM

2-RIN

(Use RD = 1 kΩ)

3-RO

(Use RD = 1 kΩ)

4-FL

5-FH