Filters low pass filter high pass filter and band pass filter

filters

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Filters
Prepared by: Sir Demy
Lesson 1
Introduction to Filters
Filtersare networks whose gain (or attenuation) and associated phase shift vary with frequency. This
frequency dependency can be exploited in order to separate wanted and unwanted components of a
signal on the basis of frequency. In general, filters consists of linear elements such as resistors,
capacitors, and inductors. Inductors are widely used at radio frequencies where the required values are
a convenient size. At lower frequencies, resistance-capacitance filters tend to predominate in view of
the physical size and cost of the components required to produce sufficiently high values of inductance.
Examples:
1. Treble control (HPF)
2. Bass Control (LPF)
3. Equalizers (BPF, BRF)
Filters are classified as:
1. Passive
2. Active
Passive filters
These filters use passive components. They use resistive and reactive components alone.
Advantages:
1. Physical simplicity
2. Operation at almost any required frequency
3. Lack of power supply requirements
Disadvantages:
1. The source and the load impedances must be taken into account when
calculating the characteristics of the filter.
2. The gain is always less than 1.
Active Filters
These filters use the passive components in conjunction with some form of amplifying circuits (op-amps
or transistors) and can therefore produce power gain more than unity.
Advantages:1. Can provide amplification of signals as well as filtering.
2. They are not affected by the load.
3. Can be constructed with its passive components are resistors and resistors only.
Inductors are not used in active filters.

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Figure B shows the frequency response of the filter
Figure C shows the Bode Gain Plot (Logarithmic) of the filter.
Note that the first-order filter has a 20dB/decroll-off.

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f
L
f
L

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FIRST-ORDER LOW PASS FILTER
The PASSIVE First-Order Low-Pass Filter (n=1)

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2
nd
order BPF (HP-LP Combination)

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