2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 1

• Chapter 3 Cascode amplifiers• Chapter 4 Differential amplifiers• Examples

Cascode amplifier

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 2

Small signal model

Differential amplifierWhy differential?

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 3

Single ended output Differential output

Noise reductionNoisy VDD

What is wrong in this picture?

Basic differential pair

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 4

Input‐output characteristics of a differential pair

Contstant tail current ISSWe can increase the current at one side if it is decreased at the other side ID1 = ‐ID2

What will happen if Vin1= Vin2 and the input voltage is increasing?

Common mode response

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 5

Tail current source with finite output resistance

Common mode, output sving

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 6

Differential gain

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 7

1 2

1 2

out outv m D

in in

V VA g RV V

2m

v DgA R

Differential gain

Single ended output

Differential mode gain

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 8

v m DA g RDifferential gain

1

2

m Dv

m S

mD

g RAg R

g R

Single ended output

Common mode gain

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 9

,

/ 21/ (2 )

out Dv

in CM m SS

V RAV g R

MOS loads

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 10

1( // // )

v mN oN oPmP

mN

mP

A g r rg

gg

( // )v mN oN oPA g r r

Variable gain

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 11

1outm D

in

V g RV

2out

m Din

V g RV

Gain varied by controlvoltage Vcont

Gilbert cell

2013‐01‐16 IL2218 Analog electronics, advanced course    KTH/ICT/EKT  VT13  /BM 12

VOUT kVinVcont

Widely used in radio circuits as mixer and phase detector