Electronic filters electronic air filter are electronic circuits which perform signal processing functions. Electronic filters can be:
- passive or active
- analog or digital
- discrete-time (sampled) or continuous-time
- linear or non-linear
The most common types of electronic filters are linear filters, regardless of other aspects of their design. See the article trion air filter on linear filters for details on their design and analysis. Most filters are a type of resonant system.
History
The oldest forms of electronic filters are passive analog linear filters, constructed using only resistors and capacitors or resistors and inductors. These are known as RC and aquarium filter RL single pole filters respectively. More complex mutipole LC filters have also been in existence for many years and the operation of such filters is well understood with many books having been written about them.
Hybrid filters have also been made, typically 1969 road runner six pack air filter assembly involving combinations of analog amplifiers replacement filter cartridge with mechanical web filter reverse osmosis water filter resonators or delay lines. Other devices such as CCD delay lines have also been used air filter as discrete-time filters.With the availability of digital signal processing, active digital filters reverse osmosis filter have become common.
Classification drinking water filter by technology
Passive filters
Single pole types
The simplest electronic implementations of linear filters are based on combinations of resistors, inductors and capacitors. These filters exist in so-called RC, RL, LC and RLC varieties. news filter All these types are collectively known as passive filters, because they do not depend upon an external power supply. Inductors block high-frequency signals and conduct low-frequency signals, while capacitors do the reverse. A filter in which the signal passes water filter systems through an inductor, or in which a capacitor provides a path to earth, therefore presents less attenuation to low-frequency signals than high-frequency oil filter cross reference 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 noise 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.
At very high frequencies (above about 100 megahertz), sometimes the inductors consist of single loops or strips of sheet metal, and the capacitors consist water filter system of adjacent strips of metal. These are called stubs.
Multipole types
Second order filters are measured by their quality or "Q" factor. A filter is said to have a high Q if it selects or rejects a narrow range of frequencies compared with its centre frequency. Q is defined as center frequency/3dB bandwidth.
Active filters
Active filters are implemented using a combination of passive and active (amplifying) components. Operational amplifiers are frequently used in active filter designs. These can have high Q, and achieve resonance without the use of inductors. However, their upper frequency limit is limited by the bandwidth of the amplifiers used.
Digital filters
Digital signal processing allows the inexpensive construction of a wide variety of filters. The signal is sampled and an analog to digital converter turns the signal into a stream of numbers. A computer program running on a CPU or a specialized DSP, less often a hardware implementation home water filter of the algorithm, calculates an fram oil filter output us filter number stream. This output is converted to a signal by passing it through a digital to analog converter. There are problems american air filter with noise introduced by the conversions, but these can be controlled and limited for many useful filters. Due to internet filter the sampling involved, the input signal must be of limited frequency content or aliasing will occur. See also: Digital filter.
Other filter technologies
Quartz filters and piezoelectrics
In the late 1930s, engineers realized that small mechanical systems made of rigid materials such as quartz would acoustically resonate at radio frequencies, i.e. from audible air cleaner filter frequencies (sound) up to several anti spam filter hundred megahertz. Some early resonators were air filter cleaning made filter queen of steel, but quartz quickly became favored. The biggest advantage of quartz is that it is piezoelectric. This means that quartz resonators can directly convert their home air filter own mechanical motion into electrical k&n filter signals. fuel filter Quartz also has a very low coefficient of thermal expansion which water filter means that quartz resonators can produce stable frequencies over a wide temperature range. Quartz crystal filters have much higher quality factors hepa furnace filter filter than LCR filters. When higher stabilities are required, the crystals and their driving circuits may be mounted in a "crystal oven" to control the temperature. For very narrow band filters, sometimes several crystals are operated in series.
Engineers realized that a large number of crystals could be collapsed into a single component, by mounting comb-shaped evaporations of metal on a quartz crystal. In this scheme, a "tapped air purifier filter delay line" reinforces the desired frequencies as the sound waves flow across the surface of the quartz crystal. The tapped delay line has become a general scheme of making high-Q filters in many different ways.
SAW filters
SAW (Surface Acoustic Wave) home water filter systems filters are electromechanical devices commonly used in radio frequency applications. Electrical signals are converted to anti-spam filter a mechanical wave in a piezoelectric crystal; ceramic filter this wave is delayed as it propagates shower filter across the crystal, before being converted back to an electrical signal by further electrodes. The delayed outputs are recombined to filter produce a direct analog implementation reverse osmosis filter system of a finite impulse response filter. This hybrid filtering technique is also found in an analog sampled filter.
Garnet filters
Another method of filtering, at frequencies honeywell air filter from 800MHz to about 5GHz, is to pool filter system use a synthetic single-crystal garnet sphere made of a chemical combination of titanium, pool filter iron internet content filter and nitrogen. The garnet sits on a strip of metal driven by a transistor, oil filter pond filter and a small loop antenna spam filter touches the top of the sphere. everpure filter An electromagnet changes ac3 filter the frequency that the garnet will pass. The advantage of this method is that the garnet internet filter filter spam software can be tuned over a very wide frequency by varying the strength of the magnetic field.
Atomic filters
For even higher frequencies k&n air filter and greater precision, the vibrations of atoms must be used. Atomic clocks use caesium masers as ultra-high Q filters to stabilize their primary oscillators. Another method, used at high, fixed frequencies with very weak radio signals, is to water filter cartridges use a ruby maser tapped delay line.
See also
- Analog filter
- Digital filter
- Passive filter
- Active filter
- Linear filter
- Non-linear filter
- Resonance
- Q factor
- Audio crossover
- Tone control circuits
- Butterworth filter
- Chebyshev filter
- Bessel filter
- Elliptic filter
- Optimum "L" filter
- Gaussian filter
- Hourglass filter
- Raised-cosine filter
- Band-pass filter
- Band-stop filter
- Low-pass filter
External links and references
- Zverev, Anatol, I (1969). Handbook of Filter Synthesis, John Wiley & Sons. ISBN 0-47-198680-1 Catalog of passive filter types and component values. The Bible for practical electronic filter design.
- Williams, Arthur B & Taylor, Fred J (1995). Electronic Filter Design Handbook, McGraw-Hill. ISBN 0-07-070441-4
- National Semiconductor AN-779 application note describing analog filter theory
- Fundamentals of Electrical Engineering and Electronics - Detailed explanation of all types of filters
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Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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