RF inductor type and its common usage
Inductors are one of the most important components in high-frequency analog circuits and signal processing for applications such as cell phones, RFID, test equipment, GPS, radar, Wi-Fi, and satellite radio. In general, several of the main functions it can undertake include circuit tuning, impedance matching, high-pass and low-pass filters, and can also be used as RF chokes.
Electronic engineers who choose to use RF inductors in their designs have many options. To simplify this choice, this article will discuss the various types of inductive components and their common usage.
Use of RF inductors
Most electronic devices contain RF inductors. “In order to track animals, there is an inductance inside the glass tube implanted in the skin of our domestic animals,†said Maria del Mar Villarrubia, a research and development engineer at PREMO. “Every time you start the car, you have two inductors. There will be wireless communication between the inside, one inside the car and the other inside the key."
Figure 1 RF inductor is one of the basic components of high-frequency electronic equipment
However, just as the ubiquity of such components, RF inductors have very specific uses. In resonant circuits, these components are typically used in conjunction with a capacitor to select a particular frequency (such as an oscillating circuit, a voltage controlled oscillator, etc.).
RF inductors can also be used in impedance matching applications to achieve impedance balancing of data transmission lines. This is necessary to ensure efficient data transfer between ICs.
When used as an RF choke, the inductor is connected in series to the circuit and acts as an RF filter. Simply put, the RF choke is a low-pass filter that attenuates higher frequencies while the lower frequencies are unobstructed.
What is the Q value?
The Q value is the most important metric when discussing inductance performance. The Q value is a measure of the performance of the inductor. It is a dimensionless parameter used to compare the oscillation frequency and the energy loss rate.
Deryl J. Kimbro, senior product manager at Murata, said: "The higher the Q value, the closer the performance of the inductor is to the ideal lossless inductor. That is, its selectivity in the resonant circuit is better."
Another benefit of high Q is the low loss, which means that the inductor consumes less energy. A low Q value results in a wider bandwidth and a lower resonance amplitude at and near the oscillation frequency.
Inductance value
In addition to the Q factor, the true measure of the inductance is of course its inductance. For audio and power applications, the value of the inductor is usually a few Henry, while high frequency applications typically require much smaller inductors, usually in the range of millihenries or microhenries.
The value of the inductance depends on several factors, including the structure, core size, core material, and actual coil turns. The inductance has both fixed inductance and adjustable inductance.
Other specifications
The inductance value is not the only important value. DC resistance, current, and self-resonant frequency (SRF) are some of the more useful specifications provided in the RF Inductance data sheet.
Del Mar Villarrubia said: "Depending on the application, each feature may be a key consideration and other characteristics. For example, if the component is to be used in a tire pressure monitoring system, the inductance is over a wide temperature range. The stability is important, and this requirement will determine the choice of core."
Rated current
When selecting an inductor, the operating current should be lower than the rated current in the specification. If the operating current exceeds the rated current, the product may be damaged.
DC resistance (DCR)
According to Kimbro, DC resistance (DCR) has a large correlation with the rated current. Based on the coil resistance, the DC resistance is equal to the loss of the inductor. If the diameter of the winding increases, the DC resistance will decrease and the rated current will increase. Larger wire diameters reduce losses and improve current handling.
Doug Lillie, product marketing manager for the Inductive Division of Vishay, said: "DC resistance limits the DC current that the device can deliver without being hot or not saturating (a sharp drop in inductance)."
Self-resonant frequency (SRF)
Each winding in the inductor can be seen as a capacitor plate. The overall effect of the capacitance between the turns and the coil and the core can be represented by a single capacitor in parallel with the inductor, called the distributed capacitor (Cd). ). The resonant frequency of this parallel structure is called the self-resonant frequency (SRF).
Lillie said: "At this frequency, the inductor looks like a pure resistor with impedance. If the frequency exceeds the self-resonant frequency, the capacitive reactance of this parallel structure will be the main factor."
Laminated chip inductor
Laminated chip inductors are fabricated using an integrated process using a ceramic material structure. Ceramic material structures provide good performance at high frequencies, while laminated chip processes provide a wide range of inductance values.
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