Phone: 86-29-88685333
Mobile: 86-13620067891
E-mail: fks@fks-coils.com
Add：C2 Building, Western Cloud Valley, Fengxi New Town, Xixian New Area, Xi'an City, Shaanxi Province, China
Mobile: 86-13620067891
E-mail: fks@fks-coils.com
Add：C2 Building, Western Cloud Valley, Fengxi New Town, Xixian New Area, Xi'an City, Shaanxi Province, China
China's RF Inductor Supplier Explains What is RF Inductor
Time: 2022-10-20 Source: Power Magnetic Components Wholesale Author: Terry Jin
RF inductors (radio frequency inductors) serve a variety of purposes and are available in a variety of construction types to meet the performance needs of specific applications. Matching resonators, and chokes are common uses of inductors in RF circuits. Matching involves eliminating impedance mismatches and minimizing reflections and losses in circuit blocks such as an antenna and a line between an RF block or an intermediate frequency (IF) block. Resonance is used in synthesizers and oscillator circuits to tune the circuit and set the desired frequency.
When RF inductors used as choke coils, inductors can be placed in the power lines of functional components such as RF modules or IF modules to attenuate high-frequency AC currents. Bias tees allow DC current to bias active devices, such as diodes. The DC bias current and AC/RF signal are added together and output from the AC+DC output port.
RF Inductor Specifications
Inductance is the property of an electrical conductor that resists changes in the current flowing through it. It is defined as the ratio of the induced voltage to the rate of change of the current that produces the induced voltage, in henries (H). RF inductors typically have inductance ratings in the range of about 0.5 nanohenry (nH) or less to hundreds of nH. As discussed in the section below on RF inductor construction selection, inductance depends on construction, core size, core material, and number of turns. Inductors are available with fixed or variable inductance values.
The DC current rating (DCR) is related to the DC resistance in amperes. DCR determines the amount of current an inductor can handle without overheating or saturation. This is an important specification when considering the thermal performance of an inductor. Power loss increases with current and DC resistance, which results in an increase in inductor temperature. Inductors are generally rated for a specific ambient temperature, as well as temperatures above ambient due to the current flowing through the inductor. For example, a part rated at 125°C ambient temperature and raised by 15°C due to full rated current (Irms or Idc) will have a maximum part temperature of approximately 140°C.
Saturation current is the DC current that causes the inductance to drop by a specified value. The inductance drops because the core can only contain a certain amount of flux density. The saturation current is related to the magnetic properties of the inductor. DCR is related to the physical property, which describes the maximum DC current that can pass through an inductor.
Self-resonant frequency (SRF) is defined as the frequency at which the device stops operating as an inductor. Inductors have low distributed capacitance between the turns of the terminal electrode or wire-wound conductor, and the inductance of the device resonates with the distributed capacitance at the SRF. At SRF, the inductor acts as a resistor with impedance. At higher frequencies, distributed capacitance dominates.
When selecting inductors for high frequency circuits and modules, it is not enough to consider only the required inductance; the SRF should be at least 10 times higher than the operating frequency. For choke applications, SRF is the frequency with the highest impedance, which provides the best signal blocking.
The Q-factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is approximately defined as the ratio of the initial energy stored in the resonator to the energy lost within one radian of the oscillation period. The Q-factor is also defined as the ratio of the center frequency of the resonator to its bandwidth when subjected to an oscillating driving force.
A high Q value results in a narrow bandwidth, which is important if the inductor is used as part of an LC tank (oscillator) circuit or in narrow bandpass applications. High Q also results in low insertion loss, which minimizes power dissipation. All frequency-dependent real and imaginary losses are included in the measurement of Q, including inductance, capacitance, skin effect in conductors, and core losses in magnetic materials.
Normative tradeoffs
Physical RF inductors are non-ideal devices including parasitic resistances, inductances, and capacitances, which are nonlinear and complex effects that affect performance and result in trade-offs between various performance specifications. Some examples include:
Higher currents require larger wires or more strands of the same wire size to minimize losses and temperature rise and fall. Larger wires reduce DCR and increase Q at the cost of larger part size and possibly lower SRF. In terms of rated current, wire wound inductors are superior to multilayer inductors of the same size and inductance value. And the Q of wirewound inductors is much higher than multilayer inductors of the same size and inductance.
Higher current capacity and lower DCR can be achieved by using ferrite core inductors with fewer turns. However, ferrites can introduce new limitations, such as greater inductance variation with temperature, looser tolerances, lower Q, and reduced saturation current ratings. Ferrite inductors with an open magnetic structure do not saturate even at full rated current.
RF Inductor Structure Selection
Various fabrication methods have been developed to mitigate the effects of various parasitics and optimize RF inductor characteristics for the needs of specific applications.
Ceramic chip chip inductors are used for narrowband filtering in RF and microwave frequency communication equipment. They offer very high Q and very tight inductance tolerances - as low as 1%.
Ferrite or iron core chip inductors are wire wound RF choke coils that provide isolation and broadband filtering without core saturation. They offer the highest inductance and lowest DCR for a given EIA size.
Multilayer chip inductors can provide low DCR, high Q, and high temperature operation. The ceramic material structure enables high performance at high frequencies, and the multilayer process provides a wide range of inductance values. Multilayer devices can provide a wider inductance range than thin-film or air-core versions, but cannot match the inductance range or current rating of wirewounds.
Air core inductors are wire wound RF chokes that provide isolation and broadband filtering without core saturation. They offer the highest inductance and lowest DCR for a given EIA size.
Tapered and broadband inductors have high impedance over a wide bandwidth and are typically available in flying leads or surface mount packages. Tapered inductors for ultra-wideband bias tees up to 100GHz. A single cone can replace several narrowband inductors cascaded in wideband biasing applications.
RFID and NFC transponder inductors are special devices that provide high sensitivity and long read distances in transponder tags and NFC/RFID antennas. They can be optimized for applications such as tire pressure monitoring that require high performance in harsh mechanical environments and high operating temperatures.
Inductors are important components in the RF/Microwave signal chain. Specifying them correctly can be complex and requires understanding various performance tradeoffs. Once a specification is developed, numerous construction options must be sorted before the best component can be found for a specific application.
When RF inductors used as choke coils, inductors can be placed in the power lines of functional components such as RF modules or IF modules to attenuate high-frequency AC currents. Bias tees allow DC current to bias active devices, such as diodes. The DC bias current and AC/RF signal are added together and output from the AC+DC output port.
RF Inductor Specifications
Inductance is the property of an electrical conductor that resists changes in the current flowing through it. It is defined as the ratio of the induced voltage to the rate of change of the current that produces the induced voltage, in henries (H). RF inductors typically have inductance ratings in the range of about 0.5 nanohenry (nH) or less to hundreds of nH. As discussed in the section below on RF inductor construction selection, inductance depends on construction, core size, core material, and number of turns. Inductors are available with fixed or variable inductance values.
The DC current rating (DCR) is related to the DC resistance in amperes. DCR determines the amount of current an inductor can handle without overheating or saturation. This is an important specification when considering the thermal performance of an inductor. Power loss increases with current and DC resistance, which results in an increase in inductor temperature. Inductors are generally rated for a specific ambient temperature, as well as temperatures above ambient due to the current flowing through the inductor. For example, a part rated at 125°C ambient temperature and raised by 15°C due to full rated current (Irms or Idc) will have a maximum part temperature of approximately 140°C.
Saturation current is the DC current that causes the inductance to drop by a specified value. The inductance drops because the core can only contain a certain amount of flux density. The saturation current is related to the magnetic properties of the inductor. DCR is related to the physical property, which describes the maximum DC current that can pass through an inductor.
Self-resonant frequency (SRF) is defined as the frequency at which the device stops operating as an inductor. Inductors have low distributed capacitance between the turns of the terminal electrode or wire-wound conductor, and the inductance of the device resonates with the distributed capacitance at the SRF. At SRF, the inductor acts as a resistor with impedance. At higher frequencies, distributed capacitance dominates.
When selecting inductors for high frequency circuits and modules, it is not enough to consider only the required inductance; the SRF should be at least 10 times higher than the operating frequency. For choke applications, SRF is the frequency with the highest impedance, which provides the best signal blocking.
The Q-factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is approximately defined as the ratio of the initial energy stored in the resonator to the energy lost within one radian of the oscillation period. The Q-factor is also defined as the ratio of the center frequency of the resonator to its bandwidth when subjected to an oscillating driving force.
A high Q value results in a narrow bandwidth, which is important if the inductor is used as part of an LC tank (oscillator) circuit or in narrow bandpass applications. High Q also results in low insertion loss, which minimizes power dissipation. All frequency-dependent real and imaginary losses are included in the measurement of Q, including inductance, capacitance, skin effect in conductors, and core losses in magnetic materials.
Normative tradeoffs
Physical RF inductors are non-ideal devices including parasitic resistances, inductances, and capacitances, which are nonlinear and complex effects that affect performance and result in trade-offs between various performance specifications. Some examples include:
Higher currents require larger wires or more strands of the same wire size to minimize losses and temperature rise and fall. Larger wires reduce DCR and increase Q at the cost of larger part size and possibly lower SRF. In terms of rated current, wire wound inductors are superior to multilayer inductors of the same size and inductance value. And the Q of wirewound inductors is much higher than multilayer inductors of the same size and inductance.
Higher current capacity and lower DCR can be achieved by using ferrite core inductors with fewer turns. However, ferrites can introduce new limitations, such as greater inductance variation with temperature, looser tolerances, lower Q, and reduced saturation current ratings. Ferrite inductors with an open magnetic structure do not saturate even at full rated current.
RF Inductor Structure Selection
Various fabrication methods have been developed to mitigate the effects of various parasitics and optimize RF inductor characteristics for the needs of specific applications.
Ceramic chip chip inductors are used for narrowband filtering in RF and microwave frequency communication equipment. They offer very high Q and very tight inductance tolerances - as low as 1%.
Ferrite or iron core chip inductors are wire wound RF choke coils that provide isolation and broadband filtering without core saturation. They offer the highest inductance and lowest DCR for a given EIA size.
Multilayer chip inductors can provide low DCR, high Q, and high temperature operation. The ceramic material structure enables high performance at high frequencies, and the multilayer process provides a wide range of inductance values. Multilayer devices can provide a wider inductance range than thin-film or air-core versions, but cannot match the inductance range or current rating of wirewounds.
Air core inductors are wire wound RF chokes that provide isolation and broadband filtering without core saturation. They offer the highest inductance and lowest DCR for a given EIA size.
Tapered and broadband inductors have high impedance over a wide bandwidth and are typically available in flying leads or surface mount packages. Tapered inductors for ultra-wideband bias tees up to 100GHz. A single cone can replace several narrowband inductors cascaded in wideband biasing applications.
RFID and NFC transponder inductors are special devices that provide high sensitivity and long read distances in transponder tags and NFC/RFID antennas. They can be optimized for applications such as tire pressure monitoring that require high performance in harsh mechanical environments and high operating temperatures.
Inductors are important components in the RF/Microwave signal chain. Specifying them correctly can be complex and requires understanding various performance tradeoffs. Once a specification is developed, numerous construction options must be sorted before the best component can be found for a specific application.
