Filters are circuits designed to pass frequencies within a specified band while attenuating frequencies outside the band. They are classified as either passive filters using only resistors, inductors and capacitors, or active filters also using op-amps and transistors. Modern active filters avoid inductors due to their bulky, heavy and non-linear properties. Common filter types include low-pass, high-pass, band-pass and band-stop, with "ideal" filters approximated using higher-order filters.

1. FILTERS…
- PRIYA SRIVASTAVA
- 090105801
- B.TECH(E.I),III yr.

2.  A Filter is a circuit that is designed to pass a specified band of
frequencies while attenuating all the signals outside that
band.
 It is a frequency selective circuit.
 The filters are basically classified as active filters & passive
filters.
Infinite gain multiple
feedback active filter

3.  The passive filter networks use only passive elements such as
resistors, inductors and capacitors.
 The active filter circuits use the active elements such as op-
amps, transistors alongwith the passive element.
 Modern active filters do not use inductors as they are
bulky, heavy & non-linear.
 The inductors generate the stray magnetic fields. They
dissipate considerable amount of power.

4. Four types of filters - “Ideal”
lowpass highpass
bandpass bandstop

5. Realistic Filters:
lowpass highpass
bandpass bandstop

6.  filter, sometimes called a “brickwall”
 filter, can be approached by making the
 order of the filter higher and higher.

7. Low pass filter High pass
C Rfb
Rfb C Rin
+
+ Rin +
Vin +
Vin _ VO
_ VO
_
_
Band pass filter
R1 C2
C1 R2 R fb
R1 R2
Ri
+
Vin
_ +
VO
_

8. C1
R1
R1
Rfb
R2 Ri
+ C2 +
Vin VO
_
_