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Feb 26 2019

Common Applications of Filter

Warm hints: This article contains about 4500 words and reading time is about 20 mins.

Introduction

Filtering is a fundamental and important technique in signal processing. Filtering technology can extract the desired signal from various signals and filter out unwanted interference signals. A filter is an important component in the frequency domain analysis of a signal.

Classification and Applications of Filters

There are many kinds of filters, and various filters have different performance characteristics. Therefore, when selecting filters, it is usually necessary to comprehensively consider the customer's actual use environment and customer performance requirements in order to make correct, effective, and reliable choices.

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Filters are divided into analog filters and digital filters. Analog filters are used to process analog signals or continuous signals. Digital filters are used to process discrete digital signals.

Analog filters can be widely used in industrial, commercial and institutional distribution networks, such as: power systems, electrolytic plating companies, water treatment equipment, petrochemical companies, large shopping malls and office buildings, precision electronics companies, airports / ports Systems, medical institutions, etc.

Article Core

Filter

Purpose

Introduce what common applications of Filter are.

Application

Semiconductor industry.

Keywords

Filter

Catalog

Introduction


 

 

 

 

 

 

 

Common Applications of Filter

 

Communications Industry

Semiconductor Industry

Petrochemical Industry

Chemical Fiber Industry

Steel / Intermediate Frequency Heating Industry

Automotive Manufacturing

Hospital System

Theater/Sports Hall

Speech Signal Processing

Image Processing

TV, Radar

Music

Airport

Application of FIR Filter in Audio System

Application of Adaptive Filtering in Signal Processing

Application of FBAR Filter in Smart Phone


Communications Industry

Communications Industry

In order to meet the operational needs of large-scale data center equipment rooms, the UPS usage capacity in the communication power distribution system has increased significantly. According to the survey, the main harmonic source equipment of the communication low-voltage power distribution system is UPS, switching power supply, inverter air conditioner and so on.

The harmonic content generated is high, and the displacement power factor of these harmonic source devices is extremely high. By using active filters, the stability of communication systems and power distribution systems can be improved, the service life of communication equipment and power equipment can be extended, and the power distribution system can be more in line with the design specifications of harmonic environments.


Semiconductor Industry

The triple harmonics of most semiconductor industries is very serious, mainly due to the large number of single-phase rectifiers used in the enterprise. The triple harmonics belongs to the zero-order harmonic, which has the characteristics of collecting in the neutral line, causing the neutral line pressure to be too large, and even sparking phenomenon, which has great production safety hazards.

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Triple harmonics can also cause the circuit breaker to trip, delaying production time. The triple harmonics forms a circulation in the transformer, which accelerates the aging of the transformer. Severe harmonic pollution will inevitably affect the efficiency and longevity of equipment in power distribution systems.


Petrochemical Industry

Petrochemical Industry

Due to the need of production, there are a large number of pump loads in the petrochemical industry, and many pump loads are equipped with variable-frequency drive. The large number of applications of variable-frequency drive has greatly increased the harmonic content in the distribution system of the petrochemical industry.

At present, most of the variable-frequency drive rectification links use 6 pulses to convert AC into DC, so the harmonics generated are mainly 5, 7 and 11 times. The main hazards are manifestations of hazards to electrical equipment and deviations in metering. This problem can be well solved by using an active filter.


Chemical Fiber Industry

Chemical Fiber Industry


In order to greatly increase the melting rate, increase the melting quality of the glass, and extend the age of the furnace and save energy, electric flux heating equipment is commonly used in the chemical fiber industry, and electricity is directly fed into the fuel-heated glass tank kiln by means of electrodes. These devices generate a large amount of harmonics, and the spectrum and amplitude difference of the three-phase harmonics are relatively large.


Steel / Intermediate Frequency Heating Industry

Steel / Intermediate Frequency Heating Industry

The medium frequency furnace, rolling mill, electric arc furnace and other equipment commonly used in the steel industry will have a major impact on the power quality of the power grid, causing frequent overload protection actions of the capacitor compensation cabinet, serious heat generation of the transformer and power supply lines, frequent fuses, etc., and even causing The voltage drops and flickers.


Automotive Manufacturing

Automotive Manufacturing

The welding machine is an indispensable equipment in the automobile manufacturing industry. Due to the randomness, rapidity and impact characteristics of the welding machine, a large number of welding machines are used to cause serious power quality problems, resulting in unstable welding quality and high degree of automation. The power compensation system cannot work due to unstable voltage, and the reactive power compensation system cannot be used normally.


DC Motor Harmonic Control

Large DC motor places need to convert AC power to DC power through rectification equipment. Because of the large load capacity of such projects, there are serious harmonic pollution on the AC side, causing voltage distortion and causing accidents in severe cases.

The use of automated production lines and precision equipment.

In the case of automated production lines and precision equipment, harmonics can affect their normal use, causing faults in intelligent control systems, PLC systems, etc.


Hospital System

The hospital has very strict requirements on the continuity and reliability of power supply. The automatic recovery time of class 0 is T≤15S, the time of automatic recovery of class 1 is 0.5S≤T≤15S, and the time of automatic recovery of class 2 is T≤0.5. S, voltage total harmonic distortion rate THDu ≤ 3%, X-ray machine, CT machine, nuclear magnetic resonance are loads with extremely high harmonic content.


Theater/Sports Hall

Theater/Sports Hall

The thyristor dimming system and large LED equipment are harmonic sources. During the operation, a large number of third harmonics will be generated, which will not only cause the power equipment of the power distribution system to be inefficient, but also cause the strobe of the lights to be communicated. The weak electric circuit such as cable TV generates noise and even causes malfunction.

In modern telecom equipment and various control systems, digital filter applications are also extremely extensive, and some of the most successful applications are listed here.


Speech Signal Processing

Speech Signal Processing

Speech processing is one of the earliest fields of application of digital filters, and one of the first areas to promote the development of digital signal processing theory. The field mainly includes five aspects:

First, speech signal analysis. That is, the waveform characteristics, statistical characteristics, model parameters, etc. of the speech signal are analyzed and calculated;

Second, speech synthesis. That is, using dedicated digital hardware or running software on a general purpose computer to generate speech;

Third, speech recognition. That is, using dedicated hardware or a computer to recognize the words spoken by the person, or to identify the person speaking;

Fourth, voice enhancement. That is, the masked speech signal is extracted from noise or interference.

Fifth, speech coding. Mainly used for voice data compression, a series of international standards for speech coding have been established, which are widely used for communication and audio processing.


Image Processing

Digital filtering technology is successfully applied to the recovery and enhancement of still images and moving images, data compression, noise and interference, image recognition and tomography, and is also successfully applied to radar, sonar, ultrasonic and infrared signals. Visible image imaging.

In the field of modern communication technology, almost no branch is not affected by digital filtering techniques. Digital sources, such as digital communication, network communication, image communication, multimedia communication, etc., are widely used in source coding, channel coding, modulation, multiplexing, data compression, and adaptive channel equalization. The digital filter is almost impossible. Among them, the software radio technology, which is considered to be the future development direction of communication technology, is based on digital filtering technology.


TV, Radar

TV, Radar

The replacement of analog TV by digital TV is an inevitable trend. The popularity of high-definition television is just around the corner, and the accompanying video disc technology has formed an industry with a huge market; videophones and conference TV products are constantly being updated.

The achievements and standardization of video compression and audio compression technologies have led to the booming industry in the TV industry, and digital filters and related technologies are important foundations for video compression and audio compression technologies.

The radar signal occupies a very wide frequency band and the data transmission rate is also very high. Therefore, compressing the data volume and reducing the data transmission rate are the primary problems faced by the digital processing of the radar signal. Telling the emergence of digital devices has spurred advances in radar signal processing technology.

In modern radar systems, the digital signal processing part is indispensable because digital signal filtering technology is indispensable from signal generation, filtering, processing, estimation of target parameters and target imaging display. Digital filters for radar signals are one of the most active research areas today. Sonar signal processing is divided into two categories, active sonar signal processing and passive sonar signal processing. Many of the theories and techniques involved in active sonar systems are the same as radar systems.


Music

The digital filter has opened up a new situation for the music field. The digital filtering technology has shown great power in editing, synthesizing, and adding special effects such as reverberation and chorus in music. Digital filters can also be used to compose, record, and play back, or to restore the sound quality of old tapes.


Airport

The root cause of power system harmonic generation is some power transmission and distribution and power equipment with nonlinear volt-ampere characteristics. When a current flows through a non-linear load, it does not have a linear relationship with the applied voltage, and a non-sinusoidal current is formed, thereby generating harmonics. Harmonic pollution is increasingly threatening the safety, stability, and economic operation of power systems, which has a significant impact on the linear load of the same network and other users.

airport

As a convenient means of transportation, the aircraft has brought a variety of choices to people's daily transportation life, and the airport is also expanding year by year. However, in the low-voltage power distribution system of the airport, there are a large number of harmonic sources, such as airport navigation lights, DC motors, electric furnaces, rolling mills, electric welders, etc. These harmonic sources have large current distortion and wide harmonic spectrum range. The characteristics of reactive power change are fast.

The harmonics generated by such loads endanger the normal operation of the power distribution system and even cause serious electrical accidents. Taking the airport navigation lighting system as an example, the navigation light load equipment is increasing, and the airport lighting station uses a large number of thyristor dimming equipment, resulting in a large amount of harmonic current, which pollutes the power quality, while adding current and additional The thermal effect also poses a certain hazard to the safety of various electrical equipment and cable lines. Therefore, it is extremely important to analyze and manage the power harmonics of the airport navigation light station.

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At present, there are two main mainstream methods for harmonic control of power systems: passive filtering technology and active filtering technology. High-power  semiconductor dimming equipment used in airport lighting stations generates a large number of high-order harmonics (mainly all odd-order harmonics other than 3 times harmonics), while passive filters are separate for each harmonic. Designing a single resonant filter, the design parameters are related to the system impedance (the calculation of the system impedance is very cumbersome, and the system is expanded year by year, the system impedance will also change); passive filtering can not completely eliminate the harmonics, but there is the danger of amplifying the resonance; The aging of the capacitor will also make the original design resonance point offset and fail to filter out the target harmonics; the passive filter system is suitable for single-load and stable applications.

Compared with passive filters, the active filter system has high controllability and fast response (≤1ms), can compensate for each harmonic, can suppress flicker, compensate reactive power, has a multi-functional feature; The cost performance is more reasonable; the filtering characteristics are not affected by the system impedance, and the danger of resonance with the system impedance can be eliminated; and the adaptive function can automatically track and compensate for the changed harmonics.

The basic principle is to detect the harmonic current from the load circuit of the harmonic source (compensated object), and the compensation device generates a compensation current waveform with the same magnitude and opposite phase of the harmonic current to cancel the harmonic source load. The harmonic current is generated so that the grid side current contains only the fundamental component.


Application of FIR Filter in Audio System

Application of FIR Filter in Audio System

Normally, we use the IIR EQ to correct the frequency response curve of the sound system or a certain channel. This is the purpose of using this equalizer. In fact, in most cases, it can help us achieve this goal. In actual use, there is a certain difference between PEQ and GEQ, but no matter which form of EQ, as long as it is powerful enough, it can basically achieve the purpose we expected.

But unfortunately, while the IIR EQ corrects the frequency response curve of the system or channel according to our own will, it also brings a by-product – the phase response of the sound system or channel is destroyed. Moreover, the general rule is that the greater the change in the frequency response of the IIR EQ, the more severe the damage to the phase response of the corresponding system or channel.

filter

The effect of the high-pass filter (also considered to be a type of IIR EQ) on the phase in the sound system

However, in today's highly developed technology, FIR, which has been widely used in other fields such as communications, can be applied to audio systems, which is indeed a good thing.

Because it solves the problem that IIR EQ can't solve, that is, as another type of EQ, it can correct only the frequency response of the sound system without affecting its phase response; it can also only phase the sound system. Make corrections without affecting the frequency response (isn't this similar to the "all-pass filter"? Yes, but it's more flexible and functional than the AP); it also corrects the system's frequency response and phase response. .

In this way, the FIR EQ is almost omnipotent except that it does not have the ability to correct the impulse response of the system. This is true, but it also has side effects!

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Comparison of frequency response and phase processing of signals above 500 Hz using FIR processor

Because the FIR filter is a digital filter that cannot be implemented with analog circuitry, it will cost more or less time to process the signal. In other words, the audio system using the FIR filter will have additional delays, and the IIR can be implemented with analog circuits. There is no such problem. Everything has two sides. If there is a good side, it will be bad. The other side. Although, the cost of time is also a factor we must consider, but at least for the medium and high frequency signals, we do not need to be too distressed for the time cost of a few milliseconds.

The specific time cost required depends mainly on the frequency range in which FIR processing is required. The lower the frequency, the longer the period of the sound. Very simple, we can think that as the FIR of the digital signal processor, at least one period of time corresponding to the lower limit frequency of the sound signal is required to process it. For example, in an ideal situation, for a 500 Hz sound signal, the FIR filter needs to be processed for at least 2 ms. Of course, this time lag is generally acceptable. But if you want to deal with signals as low as 50Hz, it may take 20ms or even longer, which will become a very annoying problem for live performances.

Generally speaking, the audio industry must be constantly making choices. Because there is never a best solution, only a more appropriate solution for the moment. For a better frequency response phase response, we will consider using a FIR filter, but at the same time we don't want too much delay in the system. Therefore, in reality, many manufacturers choose to use the FIR to process the mid-high frequency part of the system, while the IIR EQ and the classic crossover circuit handle the low frequency and ultra low frequency parts.


Application of Adaptive Filtering in Signal Processing

The various applications of adaptive filters mainly include:

1. System modeling, in which an adaptive filter is used as a model to estimate the characteristics of an unknown system.

2. An adaptive noise canceller, wherein the adaptive filter is used to estimate and cancel a noise component in the desired signal;

3. A digital communication receiver in which an adaptive filter is used for channel identification and provides an equalizer for inter-symbol interference;

4. An adaptive antenna system in which an adaptive filter is used for beam direction control and a zero point is provided in the beam pattern to eliminate unwanted interference.

filter

System identification or system modeling

For a real physical system, people are mainly concerned with their input and output characteristics, that is, the transmission characteristics of the signal, without requiring a complete understanding of its internal structure. The system can be one or more inputs or one or more outputs. The identification problem of communication systems is a very important issue in communication systems. The so-called system identification essentially estimates or determines the characteristics of the system and the unit impulse response or transfer function of the system based on the input and output signals of the system.

System identification and modeling is a very broad concept that is important in areas such as control, communication, and signal processing. In fact, system identification and modeling are not limited to traditional engineering fields, but can also be used to study social systems, economic systems, and biological systems.

This section only discusses system identification and modeling issues in communication and signal processing. The filter is used as a model of the communication channel, and the communication channel is identified by the method of adaptive system identification, so that the communication channel can be further balanced.

filter

If you think of the communication channel as a "black box", only know the input and output of the "black box"; use an adaptive filter as the model for this "black box" and make the filter have the same input and output as the "black box" . The adaptive filter "modulates" the output of the filter with the output of the "black box" by modulating its own parameters.

"Match" here generally refers to a match in the sense of least squares. In this way, the filter simulates the transmission behavior of the communication channel to the signal. Although the structure and parameters of the adaptive filter are not the same as the actual communication channel, they maintain a high degree of consistency in the input and output responses.

Therefore, in this sense, the adaptive filter is the model of this unknown "black box" system. It can also be found that if the adaptive filter has enough degrees of freedom (adjustable parameters), the adaptive filter can simulate this "black box" to any degree.

Assuming that the unknown channel is a finite impulse response (FIR) structure, an adaptive filter of FIR structure is constructed, and a pseudo-random series is used as the input signal x(n) of the system, and is simultaneously sent to the unknown channel system and the adaptive filter.

Adjusting the coefficients of the adaptive filter to minimize the mean square error of the error signal e(n), the output y(n) of the adaptive filter is approximately equal to the output d(n) of the communication system. It can be proved that the presence of additive noise v(n) does not affect the final convergence of the adaptive filter to the optimal Wiener solution.

It can be considered that two FIR systems with the same input and similar outputs should have similar characteristics. Therefore, the characteristics of the adaptive filter or its unit impulse response can be used to approximate the characteristics or unit impulse response of an unknown system.


Application of FBAR Filter in Smart Phone

A very important part of modern smartphones is the radio frequency (RF) filter. As its basic principle, filters are mainly used to pass and reject unwanted frequencies so that many receivers in the handset can process only the expected signals. 

filter

In the past, mobile phones usually only operated in a few frequency bands in specific regions of the world. However, for modern mobile phones, they basically work in multiple wireless bands at the same time, including mobile communications, Bluetooth, WiFi, and GPS. Manufacturers also want to design products that can work in different regions of the world and different telecom operators. To make mobile phones work in more frequency bands and regions, mobile phones are increasingly demanding RF filtering.

filter

In previous generations of wireless technologies, the filtering requirements were not difficult to achieve, and only surface acoustic wave filters may be used, but as carrier networks evolved to CDMA and 3G, in order to utilize current 4G/LTE services, Smartphones themselves have become more complex, so handset manufacturers have begun to expand their adoption of FBAR technology to address the unique issues facing 4G/LTE that will be discussed below.

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4G/LTE mobile phones that can operate in multiple frequency bands

The latest smartphone products must be designed to operate in multiple frequency bands around the world. The overall size of a multi-band smartphone is no larger than the previous generation, so if you want to add more filters to the same space reserved for the RF front-end circuitry. So, obviously, the filter itself must be very small. With Microcap micro-package technology, FBAR filters can satisfy most space-constrained applications in chip-scale packages.

Since FBAR is a matrix type material, it can provide very good power processing capability without using parallel structures as common in SAW filters. In addition, the size of FBAR devices will also shrink with increasing frequency, which makes FBAR very Suitable for current 4300MHz to 2700MHz, and new 3.5G/LTE band applications in the future.

4G/LTE smartphone running at higher data rates

Compared with 3G services, the download speed of 4G/LTE can reach 10 times under the same data volume, which means that the amount of data that can be downloaded in the same time is 10 times. There are several ways to achieve higher speed. Data rate, 4G/LTE will use different modulation methods according to the detected signal strength. Simply put, the higher the signal-to-noise ratio, the higher the data rate, such as conversion from QPSK to QAM16/64 modulation.

On multi-band 4G/LTE handsets with multiple single-pole multi-throw switches combined with multiple duplexers, the detected signal may be too low and affect the data rate. The low insertion loss of FBAR helps to maximize the input signal strength. Higher data throughput for a better user experience and higher data capacity.

A mobile phone with frequency division multiplexing modulation uses a duplexer that allows simultaneous signal transmission and reception. Since the transmit and receive filters are connected to the same antenna port, filter isolation between each other is very important, and higher isolation is possible. Minimize noise in the receive band, which increases SNR and data rate.

Another way to increase the data rate is to increase the download data rate by carrier aggregation and carrier aggregation in more than one frequency band. Some new LTE frequency bands occupy relatively small spectrum, so this is a network operator can effectively improve The method of communication capacity.

Since the transmission and reception of each band will work simultaneously, the switch cannot be used, so that the multiplexer is used to combine the various transmit and receive filters onto the same antenna port. When combined in a multiplexer configuration, Avago's FBAR Filters provide a low signal loss path that helps maximize data rates.

Smartphone uses multiple wireless signals simultaneously

It is difficult to find a smart phone without Wi-Fi connection function. Depending on the working frequency of the mobile phone, if the filter is not properly filtered, the signal sent by the mobile phone may interfere with the normal operation of Wi-Fi.

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When using a smartphone as a Wi-Fi hotspot, Wi-Fi will work with 4G/LTE wireless signals. Without excellent filtering capabilities, Wi-Fi transceivers may be obscured or transmitted by LTE signals on the Band 7 band. influences.

Most mobile phones today also support GPS and even GLONASS services. Since GPS/GLONASS signals usually have very low power, about -125dBm ~ -150dBm, all transmitting signals close to GPS frequency may affect GPS/GLONASS receivers. Sensitivity, the AGPS-F001 pre-filter plus LNA module provides excellent out-of-band shading and good linearity for mobile networks, PCS and WiFi signals due to its steep filtering and wideband attenuation.


Technical Advantages of FBAR

Battery life is an important feature that is often used to test and compare mobile phones. On the receiving side, we discuss how the lower insertion loss of FBAR can be compensated for by the higher loss caused by the combination of multiple bands in the RF front-end. Another benefit of the higher data rate of 4G/LTE mobile phones is that by enabling mobile phones to detect weaker signals, the coverage of mobile communications can be expanded to avoid poor reception or even dropped calls.

On the transmit side, the lower transmit filter insertion loss represents the lower output power required by the power amplifier at the same antenna transmit power, and the insertion loss due to Avago's Band 4 duplexer compared to other filter technologies. The improvement is about 0.2dB ~ 0.5dB, which is equivalent to saving up to 50mA of current consumption, thus providing longer battery life and talk time.

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When most applications are still based on 3G services, only a few frequency bands can benefit from FBAR technology. With the popularity of 4G/LTE multi-band smartphones, the advantages of FBAR technology, such as low insertion loss, steep filter curve, high isolation And miniaturized dimensions have become the reason why all major smartphone manufacturers are quickly introducing this technology.

Filters, duplexers and multiplexers using FBAR technology have been introduced into smartphone designs in 15 different operating bands in the US, Europe and Asia. With the emergence of new filtering challenges, FBAR technology will continue to be Providing answers to preferences and becoming mainstream technology.

The application fields of filters are so extensive that it is simply impossible to enumerate them completely. In addition to the above several fields, there are many other application areas. For example, it is widely used in navigation, guidance, electronic countermeasures, and battlefield reconnaissance; it is applied to energy distribution planning and automatic detection in power systems; it is applied to automatic monitoring of air pollution and noise interference in environmental protection. It is used in the economic field for stock market forecasting and economic benefit analysis.


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Principle and Function of the Filter

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Applications of Adaptive Filtering

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