5 filter passive

8/4/2019 5 FILTER Passive

1/29

FILTER


2/29

A filter is a device that passes electricsignals at certain frequencies or

frequency ranges while preventing the

passage of others.Electronic filters are electronic circuits

which perform signal processing

functions, specifically to remove

unwanted frequency components fromthe signal, to enhance wanted ones, or

both.


3/29

Passive or active

Analog or digitalHigh pass, low pass, bandpass.


4/29

Combinations of resistors (R),

inductors (L) and capacitors (C)

Do not depend upon an externalpower supply


5/29

RC and RL filters,

L-section, T-section and -section


6/29

An active filter is a type of analog electronic

filter.

Combination of passive and active (amplifying)

components,

Require an outside power source.

Op-amps are frequently used in active filter

designs.

These can have high Q factor and can achieveresonance without the use of inductors.

However, their upper frequency limit is limited

by the bandwidth of the amplifiers used.


7/29

Passive filter:

1. Using passive components such as resistors,

capacitors , inductors etc

2. No power consumption.3. low voltage gain.

Active filter:

1. Using active components such as transistor,

op amps etc

2. need power source

3. can have high voltage gain


8/29

PASSIVE FILTER

Speaker

Power supply

Filters in power distribution networks etc

ACTIVE FILTER

Instrumentation Communication

Audio application

Biomedical systems

etc


9/29

Inductors block high-frequency signals and

conduct low-frequency signals,

Capacitors do the reverse.

Resistors have no frequency-selectiveproperties, but are added to inductors and

capacitors to determine the time-constants

of the circuit, and therefore the frequencies

to which it responds.


10/29

Passive filter can be divided into three (3)

types:

i. Low pass filter

ii. High pass filteriii. Band pass filter


11/29

Cut-off frequency - a frequency level above

or below which a device fails to respond or

operate efficiently .the cutoff frequency

reduces energy flow through the device andprevents it from working as designed.

Frequency pass-band - The range of

frequencies that can pass through the filter.


12/29

Frequency bandwidth - the frequency range

between two specified frequency cut-off

points (c), that are 3dB below the maximum

centre or resonant peak while attenuating orweakening the others outside of these two

points.


13/29

Consists of a resistor and capacitor .

The capacitive reactance, (Xc) will be very

large compared to the resistive value of theresistor, R


14/29

As a result the voltage across the capacitor, Vc

will also be large while the voltage drop across

the resistor, Vr will be much lower.

At high frequencies the reverse is true with Vc

being small and Vr being large.

A filter in which the signal passes through an

inductor, or in which a capacitor provides a

path to ground, presents less attenuation to

low-frequency signals than high-frequency

signals


15/29

= RC

Gain (dB) = 20 log Vout

Vin


16/29


17/29

an input voltage across the series

combination of a capacitor and a resistor

and using the voltage across the resistor asan output.
http://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Capacitor


18/29

If the signal passes through a capacitor, or

has a path to ground through an inductor,

then the filter presents less attenuation to

high-frequency signals than low-frequency

signals.


19/29

The circuit gain, Av which is given as

Vout/Vin (magnitude) and is calculated as:

Gain (dB) = 20 log VoutVin


20/29


21/29

By connecting or "cascading" together a single

Low Pass Filter circuit with a High Pass Filter

circuit, produces a Band Pass Filter. Band Pass Filters passes signals within a certain

"band" or "spread" of frequencies without

distorting the input signal or introducing extra

noise.


22/29

This band of frequencies can be any width

and is commonly known as the filters

Bandwidth.

Bandwidth is defined as the frequency range

between two specified frequency cut-off

points (c), that are 3dB below the maximum

centre or resonant peak while attenuating or

weakening the others outside of these two

points.


23/29

BW = HL

The upper and lower cut-off frequency points

for a band pass filter can be found using the

same formula as that for both the low and highpass filters, For example.


24/29


25/29

High-pass filters attenuation of frequencies

below their cut-off points.

Low-pass filters attenuation of frequencies

above their cut-off points. Band-pass filters attenuation of frequencies

both above and below

those they allow to pass.


26/29

1. Explain the frequency response for thefollowing filter below:-

i. Low pass filter

ii. High pass filteriii. Bandpass filter


27/29

The Bode Plot shows the Frequency

Response of the filter to be nearly flat for

low frequencies and all of the input signal is

passed directly to the output, resulting in a

gain of nearly 1, called unity, until it reaches

its Cut-off Frequencypoint ( c ).


28/29

This is because the reactance of the

capacitor is high at low frequencies and

blocks any current flow through the

capacitor. After this cut-off frequency point

the response of the circuit decreases giving a

slope of -20dB/ Decade or (-6dB/Octave)

"roll-off" as signals above this frequency

become greatly attenuated, until at very

high frequencies the reactance of the

capacitor becomes so low that it gives the

effect of a short circuit condition on the

output terminals resulting in zero output.


29/29

For this type ofLow Pass Filter circuit, all

the frequencies below this cut-off, c point

that are unaltered with little or no

attenuation and are said to be in the filters

Pass band zone. This pass band zone also

represents the Bandwidth of the filter. Any

signal frequencies above this point cut-off

point are generally said to be in the filters

Stop band zone and they will be greatly

attenuated.

5 filter passive

Documents