17-01-2013, 12:33 PM
A Report Of Mini Project on BAND PASS FILTER
BAND PASS FILTER.docx (Size: 327.64 KB / Downloads: 38)
FILTERS:
Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both. Electronic filters can be:
• passive or active
• analog or digital
• high-pass, low-pass, bandpass, band-reject (band reject; notch), or all-pass.
• discrete-time (sampled) or continuous-time
• linear or non-linear
• infinite impulse response (IIR type) or finite impulse response (FIR type)
The oldest forms of electronic filters are passive analog linear filters, constructed using only resistors and capacitors or resistors and inductors. The se are known as RC and RL single-pole filters respectively. More complex multipole LC filters have also existed for many years, and their operation is well understood.
Hybrid filters are also possible, typically involving a combination of analog amplifiers with mechanical resonators or delay lines. Other devices such as CCD delay lines have also been used as discrete-time filters. With the availability of digital signal processing, active digital filters have become common. A filter is a device that passes electric signals at certain frequencies or
frequency ranges while preventing the passage of others. — Webster.
Filter circuits are used in a wide variety of applications. In the field of telecommunication,
band-pass filters are used in the audio frequency range (0 kHz to 20 kHz) for modems
and speech processing. High-frequency band-pass filters (several hundred MHz) are
used for channel selection in telephone central offices. Data acquisition systems usually
require anti-aliasing low-pass filters as well as low-pass noise filters in their preceding signal conditioning stages. System power supplies often use band-rejection filters to suppress the 60-Hz line frequency and high frequency transients.
In addition, there are filters that do not filter any frequencies of a complex input signal, but
just add a linear phase shift to each frequency component, thus contributing to a constant
time delay. These are called all-pass filters.
Passive filters:
Passive implementations of linear filters are based on combinations of resistors ®, inductors (L) and capacitors ©. These types are collectively known as passive filters, because they do not depend upon an external power supply and/or they do not contain active components such as transistors.
Inductors block high-frequency signals and conduct low-frequency signals, while capacitors do the reverse. 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 and is a low-pass filter. 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 and is a high-pass filter. Resistors on their own have no frequency-selective properties, but are added to inductors and capacitors to determine the time-constants of the circuit, and therefore the frequencies to which it responds.
The inductors and capacitors are the reactive elements of the filter. The number of elements determines the order of the filter. In this context, an LC tuned circuit being used in a band-pass or band-stop filter is considered a single element even though it consists of two components.
At high frequencies (above about 100 megahertz), sometimes the inductors consist of single loops or strips of sheet metal, and the capacitors consist of adjacent strips of metal. These inductive or capacitive pieces of metal are called stubs.
PASSIVE LOW PASS FILTER:
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter. A band-pass filter is a combination of a low-pass and a high-pass.
Low-pass filters exist in many different forms, including electronic circuits (such as a hiss filter used in audio), anti-aliasing filters for conditioning signals prior to analog-to-digital conversion, digital filters for smoothing sets of data, acoustic barriers, blurring of images, and so on. The moving average operation used in fields such as finance is a particular kind of low-pass filter, and can be analyzed with the same signal processing techniques as are used for other low-pass filters. Low-pass filters provide a smoother form of a signal, removing the short-term fluctuations, and leaving the longer-term trend.
PASSIVE HIGH PASS FILTER:-
A high-pass filter (HPF) is a device that passes high frequencies and attenuates (i.e., reduces the amplitude of) frequencies lower than its cutoff frequency. A high-pass filter is usually modeled as alinear time-invariant system. It is sometimes called a low-cut filter or bass-cut filter.[1]
High-pass filters have many uses, such as blocking DC from circuitry sensitive to non-zero average voltages or RF devices. They can also be used in conjunction with a low-pass filter to make abandpass filter. The actual amount of attenuation for each frequency is a design parameter of the filter.
.PASSIVE BAND PASS FILTER:
A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.
Optical band-pass filters are of common usage.
An example of an analogue electronic band-pass filter is an RLC circuit (a resistor–inductor–capacitor circuit). These filters can also be created by combining a low-pass filter with a high-pass filter.
Bandpass is an adjective that describes a type of filter or filtering process; it is frequently confused with passband, which refers to the actual portion of affected spectrum. Hence, one might say "A dual bandpass filter has two passbands." A bandpass signal is a signal containing a band of frequencies away from zero frequency, such as a signal that comes out of a bandpass filter.