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Encyclopedia > Electronic filter
Television signal splitter consisting of a hi-pass filter (left) and a low-pass filter (right). The antenna is connected to the screw terminals to the left of center.

Electronic filters are electronic circuits which perform signal processing functions, specifically intended to remove unwanted signal components and/or enhance wanted ones. Electronic filters can be: Image File history File links Download high resolution version (1493x941, 702 KB) Summary Television signal splitter, consisting of a hi-pass and a lo-pass filter. ... Image File history File links Download high resolution version (1493x941, 702 KB) Summary Television signal splitter, consisting of a hi-pass and a lo-pass filter. ... An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes. ... Signal processing is the processing, amplification and interpretation of signals, and deals with the analysis and manipulation of signals. ...

The most common types of electronic filters are linear filters, regardless of other aspects of their design. See the article on linear filters for details on their design and analysis. A passive component is an electronic component that does not require a source of energy to perform its intended function. ... An example of high-pass active filter. ... It has been suggested that this article or section be merged with Analog electronics. ... An FIR filter In electronics,nirali a digital filter is any electronic filter that works by performing digital mathematical operations on an intermediate form of a signal. ... Discrete time is non-continuous time. ... Continuous time occurs when time is sampled continuously. ... A linear filter applies a linear operator to a time-varying input signal. ... A non-linear filter is a signal-processing device whose output is not a linear function of its input. ... IIR (infinite impulse response) is a property of signal processing systems. ... A finite impulse response (FIR) filter is a type of a digital filter. ... A linear filter applies a linear operator to a time-varying input signal. ...

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 RL single pole filters respectively. More complex multipole LC filters have also existed for many years and the operation of such filters is well understood with many books having been written about them. An ideal resistor is a component with an electrical resistance that remains constant regardless of the applied voltage or current flowing through the device. ... See Capacitor (component) for a discussion of specific types. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ...

Hybrid filters have also been made, typically involving combinations 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 specially developed CCD used for ultraviolet imaging in a wire bonded package. ... The term delay line has multiple meanings: In electronics and derivative fields such as telecommunications, a delay line is rigorously defined as a single-input-channel device, in which the output channel state at a given instant, t, is the same as the input channel state at the instant t...

## Classification 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. 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 through an inductor, or in which a capacitor provides a path to earth, therefore 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. Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... See Capacitor (component) for a discussion of specific types. ... resistor-capacitor circuit (RC circuit), or RC filter or RC network, is one of the simplest analogue electronic filters. ... This article does not cite any references or sources. ... An LC circuit consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. When connected together, an electrical current can alternate between them at an angular frequency of where L is the inductance in henries, and C is the capacitance in farads. ... An RLC circuit (also known as a resonant circuit or a tuned circuit) is an electrical circuit consisting of a resistor (R), an inductor (L), and a capacitor (C), connected in series or in parallel. ... See Capacitor (component) for a discussion of specific types. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ... A low-pass filter is a filter that passes low frequencies but attenuates (or reduces) frequencies higher than the cutoff frequency. ... A high-pass filter is a filter that passes high frequencies well, but attenuates (or reduces) frequencies lower than the cutoff frequency. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ...

#### 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 central frequency divided by 3dB bandwidth. This article or section does not cite any references or sources. ...

### Active filters

Active filters are implemented using a combination of passive and active (amplifying) components, and require an outside power source. 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. An example of high-pass active filter. ... A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with Differential Inputs and, usually, a single output. ... In an electrical circuit, resonance occurs at a particular frequency when the inductive reactance and the capacitive reactance are of equal magnitude, causing electrical energy to oscillate between the magnetic field of the inductor and the electric field of the capacitor. ...

### Digital filters

A finite impulse response filter

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 (or less often running on a hardware implementation of the algorithm) calculates an output number stream. This output is converted to a signal by passing it through a digital to analog converter. There are problems with noise introduced by the conversions, but these can be controlled and limited for many useful filters. Due to the sampling involved, the input signal must be of limited frequency content or aliasing will occur. See also: Digital filter. A Finite Impulse Response EQ, by iluvcapra File links The following pages link to this file: Digital filter Electronic filter Categories: GFDL images ... Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. ... This article or section should include material from AD converters In electronics, an analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. ... â€œCPUâ€ redirects here. ... A digital signal processor (DSP) is a specialized microprocessor designed specifically for digital signal processing, generally in real-time. ... In mathematics, computing, linguistics, and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will terminate in a defined end-state. ... In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analogue signal (current, voltage or charges). ... Properly sampled image of brick wall. ... An FIR filter In electronics,nirali a digital filter is any electronic filter that works by performing digital mathematical operations on an intermediate form of a signal. ...

### 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 frequencies (sound) up to several hundred megahertz. Some early resonators were made 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 own mechanical motion into electrical signals. Quartz also has a very low coefficient of thermal expansion which means that quartz resonators can produce stable frequencies over a wide temperature range. Quartz crystal filters have much higher quality factors 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. Face The 1930s (years from 1930â€“1939) were described as an abrupt shift to more radical and conservative lifestyles, as countries were struggling to find a solution to the Great Depression, also known in Europe as the World Depression. ... Quartz (from German Quarz[1]) is the second most common mineral in the Earths continental crust. ... Sound is a disturbance of mechanical energy that propagates through matter as a wave. ... For other uses, see Steel (disambiguation). ... Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. ... A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. ...

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 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) filters are electromechanical devices commonly used in radio frequency applications. Electrical signals are converted to a mechanical wave in a piezoelectric crystal; this wave is delayed as it propagates across the crystal, before being converted back to an electrical signal by further electrodes. The delayed outputs are recombined to produce a direct analog implementation of a finite impulse response filter. This hybrid filtering technique is also found in an analog sampled filter. SAW filters are limited to frequencies up to 3GHz. A surface acoustic wave (SAW) is a kind of wave used in piezoelectric devices called SAW devices in electronics circuits. ... In engineering, electromechanics combines electromagnetism and mechanics. ... It has been suggested that this article or section be merged with Radio waves. ... Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. ... An electrode is an electrical conductor used to make contact with a metallic part of a circuit (e. ... A finite impulse response (FIR) filter is a type of a digital filter. ... An analog sampled filter an electronic filter that is a hybrid between an analog and a digital filter. ...

#### BAW filters

BAW (Bulk Acoustic Wave) filters are electromechanical devices. These filters are in the research state for the moment. BAW filters can implement ladder or lattice filters. BAW filters seem to be smaller than SAW filters, and can operate at frequencies up to 16 GHz. In engineering, electromechanics combines electromagnetism and mechanics. ... Look up lattice in Wiktionary, the free dictionary. ...

#### Atomic filters

For even higher frequencies 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 use a ruby maser tapped delay line. Chip-scale atomic clock unveiled by NIST An Atomic Clock is a type of clock that uses an atomic resonance frequency standard to feed its counter. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser is a device that produces coherent electromagnetic waves through amplification due to stimulated emission. ... This article does not cite any references or sources. ...

## The transfer function

The transfer function $H(s)$ of a filter is the ratio of the output signal $Y(s)$ to that of the input signal $X(s)$ as a function of the complex frequency $s$: A transfer function is a mathematical representation of the relation between the input and output of a linear time-invariant system. ...

$H(s)=frac{Y(s)}{X(s)}$

with $s = sigma + j omega$.

The transfer function of all linear time-invariant filters generally share certain characteristics:

• Since the filters are constructed of discrete components, their transfer function will be the ratio of two polynomials in $s$, i.e. a rational function of $s$. The order of the transfer function will be the highest power of $s$ encountered in either the numerator or the denominator.
• The polynomials of the transfer function will all have real coefficients. Therefore, the poles and zeroes of the transfer function will either be real or occur in complex conjugate pairs.
• Since the filters are assumed to be stable, the real part of all poles (i.e. zeroes of the denominator) will be negative, i.e. they will lie in the left half-plane in complex frequency space.

In mathematics, a rational function in algebra is a function defined as a ratio of polynomials. ...

## Classification by transfer function

Filters may be specified by family and passband. A filter's family is specified by certain design criteria which give general rules for specifying the transfer function of the filter. Some common filter families and their particular design criteria are:

Generally, each family of filters can be specified to a particular order. The higher the order, the more the filter will approach the "ideal" filter. The ideal filter has full transmission in the pass band, and complete attenuation in the stop band, and the transition between the two bands is abrupt (often called brick-wall). The Butterworth filter is one type of electronic filter design. ... Chebyshev filters, are analog or digital filters having a steeper roll-off and more passband ripple than Butterworth filters. ... Chebyshev filters, are analog or digital filters having a steeper roll-off and more passband ripple than Butterworth filters. ... In electronics and signal processing, a Bessel filter is a variety of linear filter with a maximally flat group delay (linear phase response). ... An elliptic filter (also known as a Cauer filter) is an electronic filter with equalized ripple (equiripple) behavior in both the passband and the stopband. ... The Optimum L filter (also known as a Legendre filter) was proposed by Athanasios Papoulis in 1958. ... In electronics and signal processing, A Gaussian filter is designed to give no overshoot to a step function input while maximising the rise and fall time. ... The raised-cosine filter is a particular electronic filter, frequently appearing in telecommunications systems due to its ability to minimise inter-symbol interference (ISI). ...

Each family can be used to specify a particular pass band in which frequencies are transmitted, while frequencies in the stop band (i.e. outside the pass band) are more or less attenuated.

• Low-pass filter - Low frequencies are passed, high frequencies are attenuated.
• High-pass filter - High frequencies are passed, Low frequencies are attenuated.
• Band-pass filter - Only frequencies in a frequency band are passed.
• Band-stop filter - Only frequencies in a frequency band are attenuated.
• All-pass filter - All frequencies are passed, but the phase of the output is modified.

A low-pass filter is a filter that passes low frequencies but attenuates (or reduces) frequencies higher than the cutoff frequency. ... A high-pass filter is a filter that passes high frequencies well, but attenuates (or reduces) frequencies lower than the cutoff frequency. ... The frequency axis of this symbolic diagram would be logarithmically scaled. ... A generic band-stop filter, showing both positive and negative angular frequencies In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a range to very low levels. ... An all-pass filter is an electronic filter that passes all frequencies equally, but changes the phase relationship between various frequencies. ...

## Classification by topology

The above classifications will specify completely the transfer function of the filter (i.e. its electronic behavior), but it remains to choose the particular circuit topology to implement the filter. In other words, there are a number of different ways of achieving a particular transfer function when designing a circuit. These topologies may be further subdivided into passive filters and active filters. Some common circuit topologies are: An electronic filter topology is an electronic filter circuit in which the values of the components remain undefined. ... A passive component is an electronic component that does not require a source of energy to perform its intended function. ... An example of high-pass active filter. ...

Wilhelm Cauer proposed a number of electronic filter designs or circuit topologies for realization of a driving point impedance. ... A Sallen and Key filter is a type of active filter, particularly valued for its simplicity. ... Multiple feedback topology circuit. ... State Variable Topology refers to filters with two pole filter topology. ...

• Zverev, Anatol, I (1969). Handbook of Filter Synthesis. John Wiley & Sons. ISBN 0-471-98680-1.  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
• BAW filters (in French; PDF)
• Some Interesting Filter Design Configurations & Transformations
• Books and tutorials how to design RF Filters
• Analog Filters for Data Conversion

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