Inductors are components that can convert electrical energy into magnetic energy and store it. The structure of inductor is similar to that of transformer, but there is only one winding. The inductor has a certain inductance, which only blocks the change of current.   Inductance can be made of conductive material coiled around the magnetic core, typically copper wire, or the magnetic core can be removed or replaced with ferromagnetic material. The core material with higher permeability than air can restrict the magnetic field more closely around the inductive element, thus increasing the inductance. There are many kinds of inductors, most of which are made of the outer enamel coil surrounding the ferrite spool, while some protective inductors place the coil completely in the ferrite.   The cores of some inductive elements can be adjusted. Thus, the inductance can be changed. The small inductor can be directly etched on the PCB board with a method of laying spiral tracks. Small value inductors can also be used to make transistors. The same process is used in integrated circuits. In these applications, aluminum interconnects are often used as conductive materials.   No matter what method is used, based on the actual constraints, the most widely used is a circuit called "spinner", which uses a capacitor and an active element to show the same characteristics as the inductive element. Inductive elements used to isolate high frequencies are often composed of a metal wire passing through a magnetic column or bead.   There are many kinds of inductors with different shapes. The more common ones are: single-layer flat wound hollow core inductors, inter wound hollow core inductors, bodiless hollow core inductors, multi-layer hollow core inductors, honeycomb inductors, inductors with magnetic cores, magnetic can inductors, high-frequency choke coils, low-frequency choke coils, fixed inductors, etc.   The winding method of enameled wire of inductance coil on the skeleton can be divided into single-layer winding method and multi-layer winding method.   The first winding method: single layer winding method   Single layer inductance coil is widely used in today's circuit applications, and its inductance is usually only a few or dozens of micro Heng. The Q value of this kind of coil is generally high, and most of them are used in high-frequency circuits.   In the design of single-layer inductance coil, its circuit winding method usually adopts close winding method, intermediate winding method and tire free winding method. These three winding methods are also applicable to different circuit appliances.   The second winding method: multi-layer winding method   Single layer coil can only be used in occasions with small inductance, so when the inductance is greater than 300 μ H, multilayer coils should be used.   The multi-layer winding method can be divided into two types: multi-layer dense winding method and honeycomb winding method: if the coil is wound, its plane is not parallel to the rotating surface, but intersects into a certain angle, this kind of coil is called honeycomb coil. The number of times the wire bends back and forth when it rotates for one cycle is often called the number of turns. The advantages of honeycomb winding method are small volume, small distributed capacitance and large inductance.
    Complex programmable logic device (CPLD) was developed in the mid-1980s with the continuous improvement of semiconductor component technology and the continuous improvement of user requirements for device integration.   There are many manufacturers of complex programmable logic devices (CPLD), with various varieties and structures, but most of them adopt the following two structures. One is CPLD based on product term. The logic unit of this CPLD follows the product term logic unit structure of simple PLD (pal, gal, etc.). At present, most CPLDs belong to this type.   The logic block in CPLD is similar to a small-scale PLD. Usually, a logic block contains 4 ~ 20 macro units, and each macro unit is generally composed of product term array, product term allocation and programmable registers.   So, what are the application scenarios of complex programmable logic devices?   The emergence of reconfigurable PLD (programmable logic device) based on SRAM (static random access memory) has created conditions for system designers to dynamically change the logic function of PLD in operating circuits.   PLD uses SRAM units to store configuration data. These configuration data determine the interconnection relationship and logic function within the PLD. Changing these data also changes the logic function of the device.   Since the data of SRAM is volatile, these data must be stored in non-volatile memory such as EPROM, EEPROM or Flash ROM other than PLD devices, so that the system can download them to the SRAM unit of PLD at an appropriate time, so as to realize in circuit Reconfigurability (ICR).
Inductors, also known as chokes, reactors, and dynamic reactors. It is an element that can convert electric energy into magnetic energy and store energy in the magnetic field. The structure is similar to the transformer and has the characteristics of DC and AC resistance. In electronic circuits, inductance mainly plays the role of filtering, current limiting, tuning, oscillation, interference suppression and magnetic field generation.   First, let's talk about the basic principle of inductors, that is, self induction.   Self induction: electromagnetic induction phenomenon that occurs when the current flowing through the conductor itself changes. The coil is made of metal wires. When the current flowing through the coil changes, it will produce obvious electromagnetic induction phenomenon. The self induced reverse electromotive force of the coil hinders the change of the current and plays the role of stabilizing the current. Specifically, if the inductor is in the state of no current passing, it will try to prevent the current from flowing through it when the circuit is connected; If the inductor is in a state of current flow, it will try to maintain the current when the circuit is disconnected.   From the perspective of energy, the inductor can dump electric energy into magnetic energy and release magnetic energy into electric energy. The same inductor has different blocking effects on current with different changing frequencies. Its general rule is: connect low frequency and block high frequency.   The greater the number of coils and the denser the coils are wound, the greater the inductance. The inductance of the coil with magnetic core is larger than that of the coil without magnetic core; The greater the permeability of the core, the greater the inductance of the coil. The basic unit of inductance is Henry, which is represented by the letter H. Common units: milli Heng (MH), micro Heng( μ H) , nahen (NH). The conversion relationship is: 1h=10^mh=10^6 μ H=10^9nH   How to choose the right inductor?   The appropriate inductor is mainly determined according to the package size of the inductor, as well as the minimum inductance and rated working current required by the circuit design. In addition, it is also necessary to comprehensively consider the working environment of the inductor, and refer to the working frequency, working voltage and other parameters.
Ferrite beads are common anti-interference components and tools that can be used for Anti-interference components of electronic communication equipment. Because ferrite can attenuate higher frequencies and let lower frequencies pass almost unimpeded, it has been widely used in EMI control. At the same time, it has better high-frequency filtering characteristics than ordinary inductors and shows resistance at high frequencies, so it can maintain high impedance in a fairly wide frequency range, so as to improve the effect of frequency modulation filtering.. Magnetic rings / beads for EMI absorption can be made into various shapes and are widely used in various occasions.   Ferrite beads have high resistivity and permeability, which is equivalent to resistance and inductance in series, but both resistance and inductance change with frequency. It has better high-frequency filtering characteristics than ordinary inductors, showing resistance at high frequencies, so it can maintain a high impedance in a fairly wide frequency range, so as to improve the effect of FM filtering.   For example, on PCB board, it can be added to dc/dc module, data line, power line, etc. It absorbs the high-frequency interference signal on the line, but it will not produce new zeros and poles in the system and will not damage the stability of the system. When it is used with power filter, it can well supplement the performance of the high-frequency end of the filter and improve the filtering characteristics of the system.   Ferrite magnetic beads can not only be used in power circuits to filter out high-frequency noise (DC and AC output), but also can be widely used in other circuits, and its volume can be made very small. Especially in digital circuits, because the pulse signal contains high-frequency harmonics, which is also the main source of high-frequency radiation of the circuit, it can play the role of magnetic beads in this occasion. Ferrite magnetic beads are also widely used in noise filtering of signal cables and wires.
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