Abracon Provides a Technical Comparison of Advantages and Considerations When Choosing Hi-Q Thin Film Inductors, SMT Air Coils or SMT Multi-Layer Inductors

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Abracon Corporation, a globally preferred, leading supplier of frequency control and magnetic components, provides a wide selection of choices of inductor ranges for engineers to consider.

Abracon Inductor Figures 1-10

The Abracon inductor ranges referenced offer a wide selection of choices for engineers.

Choosing the correct inductor for circuit design engineers factor a number of application and commercial considerations. These include the function of the inductor in the electronic circuit, frequency of operation and inductance required, the interaction with other circuit elements, the expected current to be passed and voltage across the inductor, expected efficiency, available space and cost.

Consequently, the engineer is often faced with a tradeoff between performance, size and cost that must be considered when selecting an inductor for a design.

Inductor choice is determined by options to meet their application. This paper focuses on three technologies of inductors offered by Abracon: Air Coils (AIAC Series), High Q Thin Film (ATFC Series), and Multi-Layer Inductors (AIMC Series), outlining their strengths and considerations for use in different applications.

The Advantages of Air Coil Inductors
➢ Their inductance is unaffected by the current it carries.
➢ Air coils are free of the 'iron losses,’ which affect ferromagnetic cores. This compares to inductors using ferromagnetic cores, whose inductance reaches at peak moderate field strengths before dropping towards zero, as saturation approaches.
➢ Figure 1 illustrates that as current increases through a ferromagnetic core, the magnetic field (B) increases until saturation is reached, while the magnetic permeability (uF) peaks at relatively low levels before declining, reflecting the non-linearity of inductance.
➢ Air Coils avoid this non-linearity seen in Fig 1, and can be used in applications that cannot accept the harmonics or intermodulation distortion. These include audio and RF circuits. Hi Fi speaker crossover networks cannot tolerate the non-linearity that leads to harmonic distortion of the audio signals. Similarly, in RF transmitter circuits these cannot tolerate the non-linearity seen when inductor cores are pushed into saturation, as this leads to intermodulation distortion. Therefore, in both applications the use of Air Coils can be valuable considerations.
➢ With the requirement to operate at higher frequencies, Air Coils provide a better Q-factor, greater efficiency, greater power handling and less distortion.
➢ The Abracon AIAC-Series offers flat top Air Coil Inductors that aid SMT manufacturers, along with lead-free and RoHS compliance.
➢ The AIAC-0805C series, the smallest in the range (2.85 x 1.80 x 2.10mm), offers very low resistances from 2.6mΩ to 42.2 mΩ, over the full inductance range, of 3.9nH to 68nH, allowing higher current designs from 320mA to 1200mA.
➢ The AIAC series offers excellent Q values between 70 to 145 with SRF between 400MHz to 3.2GHz, based upon the inductor size.

Wire-Wound and Air Coil Applications
➢ Widely used in cordless phones, high frequency communication equipment, intercom, CATV
➢ Noise reduction in voltage supply/bias for RF power transistors
➢ Broadband I/O filtering, frequency selection
➢ Impedance matching

Advantages of Hi-Q Thin Film Inductors
➢ Thin Film Inductors are manufactured using a photolithographic single layer ceramic chip. This technology is commonly used in IC manufacturing, allowing higher performance parts and repeatability.
➢ The Abracon ATFC Series offers high SRF, excellent Q, with superior temperature stability over -40C to +85C. Highly stable design for critical needs.
➢ For applications that require tight tolerance, Thin Film Inductor capability allows tolerances ± 0.1nH. These tolerances contrast with wire air coils that are typically 10%. These are especially important for higher frequency RF filters when narrower B/W requirements must be guaranteed.
➢ The ATFC Series offer exceptionally high SRF, which is controlled within 10%, offering stable inductance at high frequencies.
➢ Referring to the formula for Self Resonance, SRF = 1/ {2 π √(LC)} in Hz, where L is the inductance in Henries and C is the capacitance in Farads.
➢ From this, it is evident that increases in L or C will reduce the SRF. Therefore, for a targeted inductance, capacitance needs to be kept as low as possible. Thin Film technology enables control of capacitance, keeping the SRF very high.
➢ Figure 4 shows the Thin Film Technology for Inductors.

Applications for Thin Film Inductors
Thin Film Inductors are used extensively in the following application areas:
➢ Radio frequency integrated circuits (RFICs)
➢ Low-noise amplifiers (LNA’s) [See Fig 5]
➢ Voltage controlled oscillators (VCO’s) [See Fig 6]
➢ Mixers
➢ Intermediate frequency filters (IFF’s)
➢ Matching networks
➢ Bluetooth modules
➢ WLAN cards (IEEE 802.11g, 802.11a,a+b)
➢ Cellular telephone, pagers and GPS products
➢ LNA Application: Matching Coil in this LNA design should be a high-Q type or tight inductance tolerance type coil for improved design stability.
➢ A Thin Film Inductor such as the ATFC Series is suitable for this receiver circuit, particularly due to the obtainable tight tolerances.
➢ VCO Application: The matching coil needs to be a high-Q and tolerance type for accuracy of the oscillator.
➢ A thin film inductor such as the ATFC Series is suitable for this VCO application, due to the obtainable tight tolerances.

Advantages of Multi-Layer Ceramic Inductors
➢ The AIMC range from Abracon offers a wide range of EIA sizes. Supplied in standard miniature 0201, 0402, 0603 and 0805 chip sizes, multilayer chip inductors offer tight tolerances of ±2%, ±3%, ±5%, ±10%, or ±0.1 nH, ±0.2 nH, ±0.3 nH.
➢ Multi-layer Inductors are the lowest cost solutions, and offer a wide application of uses.
➢ Multi-layer Ceramic Inductors offer high self-resonant frequency. The Abracon AIMC-0402HQ series extends the usability with minimum 44% higher Q versions, offering Qs of minimum 13, and SRF of 4GHz to 6GHz across its range.
➢ Multi-layer monolithic construction yields high reliability.
➢ Excellent solderability and heat resistance for reflow soldering.

Applications for Multi-Layer Inductors
➢ Bluetooth
➢ Mobile phones such as GSM, CDMA, PDC
➢ High frequency telecommunication circuits
➢ Other high frequency circuit general use
➢ Multi-layer Inductors are particularly suitable for noise suppression; when installed in series with signal lines, high frequency noise is suppressed. There is no need for ground termination, which makes such inductors highly suitable for circuits with difficult ground issues.
➢ Multi-layer Inductors are ideal for noise reduction in low impedance circuits. The high frequency noise is attenuated by the high impedance seen by the inductors, while lower frequency signals pass through.
➢ High-speed digital circuits also find use of the multi-layer inductors for filtering correction to circuit jitter.
➢ The monolithic ceramic construction offers minimum flux leakage, which eliminates crosstalk, particularly important in tuned circuits, allowing high-density placement.
➢ Figure 7 shows the application of Multi-layer Inductors used in RFI attenuation.

Technology and Application Summary
These three alternative inductor technologies offer choices and considerations for engineers, and ultimately the applications and circuit design drives these choices.

Inductor SRF
Inductor SRF across the different technologies shows the reduction with increased inductance. Generally, the multi-turns wire-wound inductors have the highest SRF. The Abracon AISC Series demonstrates such performance.

Inductance Ranges
Available inductance increases with the size of package, Abracon offers sizes up to EIA 0805 in the ranges discussed. Fig 9 shows the ranges of inductance across two of the common EIA sizes 0402 and 0603. Engineers need to consider the required inductance versus available package sizes.

Inductance Tolerance
Engineers must consider the size of inductor needed and the tolerances available at the value of inductance required. Where tolerance is important, the Thin Film technology has the tightest tolerance capability.

The Abracon inductor ranges referenced offer a wide selection of choices for engineers. As demonstrated in this release, the choice of inductor is driven by application, size of component and cost. Engineers should consider the performance attributes across the ranges to reach the best compromise.

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About Abracon Corporation
Abracon Corporation was established in 1992 with the vision of becoming a top tier global manufacturer of Frequency Control, Signal Conditioning, Clock Distribution and Magnetic Components with local design and technical support. Abracon provides its customers with high quality products, competitive pricing, timely delivery, reliable engineering and technical support, plus production flexibility worldwide.

Written by: Dean Clark | Technical Sales Manager, Abracon Corporation

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