Introduction to Active Network

1. ACTIVE NETWORK

2. ACTIVE FILTERS
Passive filters have several limitations
1. Cannot generate gains greater than one
2. Loading effect makes them difficult to interconnect
3. Use of inductance makes them difficult to handle
Using operational amplifiers one can design all basic filters, and more,
with only resistors and capacitors
The linear models developed for operational amplifiers circuits are valid, in a
more general framework, if one replaces the resistors by impedances
Ideal Op-Amp
These currents are
zero

3. Basic Inverting Amplifier
0V
  VVgainInfinite
0V
0 II-impedanceinputInfinite
1
1 2
0OVV
Z Z
 
2
1
1
O
Z
V V
Z
 
Linear circuit equivalent
0I
1
2
Z
Z
G 
1
1
1
Z
V
I 

4. EXAMPLE USING INVERTING AMPLIFIER
LOW PASS FILTER

5. Basic Non-inverting amplifier
1V
1V
0I 
1
1
2
10
Z
V
Z
VV


1
1
12
0 V
Z
ZZ
V


1
2
1
Z
Z
G 
01 I

6. EXAMPLE USING NON INVERTING CONFIGURATION

7. EXAMPLE SECON ORDER FILTER
2
( )V s
22 2 2
1 1 2 3
0
1/
OIN
V VV V V V
R C s R R

   
2
2 2
0
1/
O
VV
R C s
  