Lumped circuit elements, such as capacitors (C), inductors (L), and resistors (R), are the essential building blocks of tuned active and passive circuits. While the most enduring trends in these passive components have seen shrinking size and packaging suitable for surface-mount applications, performance has also improved with advances in ceramic and other materials, notably in terms of stability with temperature and time. For higher-level designs, this results in more stable filters and oscillators, among other high-frequency circuits.
While not the most glamorous of electronic building blocks, RLC elements are among the most critical, since they are used in everything from impedance-matching networks to power-supply circuitry. Capacitors, which store current in an electric field, are essentially two metallic or conductive parallel plates separated by a dielectric material. Characterized in units of Farads, they are available in a wide range of materials (such as ceramic, porcelain, and tantalum capacitors) and package styles, with fixed or variable values. Fixed capacitors for RF and microwave applications can be specified as single-layer or multilayer devices.
These components are characterized by a number of parameters, including equivalent series resistance (ESR), quality factor (Q), series resonant frequency (SRF), dissipation or loss factor, temperature coefficient, parallel resonant frequency (PRF), and DC working voltage. Several short application notes from Johanson Technology (www.johansontechnology.com) provide clear definitions of these key capacitor performance parameters. The company's application notes cover such topics as Q and ESR, SRF and PRF for RF capacitors, capacitor RF current and power, making S-parameter measurements on high-Q capacitors, and high-frequency inductor modeling. In addition, the long popular The RF Capacitor Handbook from American Technical Ceramics (www.atceramics.com) provides a comprehensive overview of RF/microwave capacitors and their applications. A copy of the handbook can be requested by completing an on-line form at the company's website.
In addition to the capacitor handbook, American Technical Ceramics has recently enhanced its on-line services with the release of an on-line Product Finder shop site. Armed with a credit card, visitors can order from a selection of multilayer-capacitor (MLC), single-layer-capacitor (SLC), resistor, and inductor design kits. The capacitor kits, for example, provide as many as 16 different capacitance values per kit, featuring the company's lines of porcelain, low-ESR microwave, and surface-mount millimeter-wave capacitors. The company was recently listed as a supplier for high-frequency MLCs according to the Defense Supply Center Columbus (DSCC) commercial-off-the-shelf (COTS) requirements for military components (www.dscc.dla.mil).
AVX Corp. (www.avx.com) offers extensive lines of SLCs and MLCs including a line of multicapacitor arrays with from 2 to 6 capacitors on a single-layer substrate. Available with a wide range of dielectric materials, these SLC arrays can even be specified with different values per pad for applications requiring nonstandard capacitance values . The firm also offers the porcelain- and ceramic-based AQ and SQ series of microwave MLCs for low-loss applications through about 4.2 GHz. AVX recently introduced its OxiCap™ line of lead-free niobium-oxide (NbO) solid-electrolytic capacitors as an alternative to tantalum devices in environmentally sensitive automotive, cellular-communications, and computer applications.
Compex Corp. (www.compexcorp.com), which recently relocated to a modern new facility in West Berlin, NJ, offers a variety of innovative chip capacitor configurations in addition to high-performance substrates and contract engineering services. The firm's two-electrode CSA series capacitors can be supplied in square or rectangular chip configurations with capacitance values ranging from 0.8 to 10,000 pF. The CSB series capacitors incorporate a full electrode on one side and a split electrode on the other side of the chip, allowing connection as two capacitors with a common electrode or as serially connected capacitors with connections on one side of the chip. The series CRO capacitor rows are multiple-device arrays with as many as eight capacitors per array and values to 1000 pF per capacitor. The typical dimensions of the row caps range from 20 × 65 mils to 40 × 125 mils. The company's recently introduced super-high-K X7R capacitors are designed with a dielectric constant of 20,000 and low dissipation factor of typically 0.015 at 1 MHz. The SLCs are available in 5- and 8-mil thicknesses with voltage ratings of 25 and 50 V, respectively, and typical capacitance values from 100 to 1000 pF.
Digi-Key Corp. (www.digikey.com) lists more than 1100 different ceramic capacitor products from a wide range of manufacturers. Visitors to the distributor's website can search for fixed-value capacitors by capacitance value, package type, temperature coefficient, capacitance tolerance (0.05, 0.10, 0.25, 0.5, 1.0, 2.0. 5.0, 20, 30 percent), vendor, and voltage rating. The company also provides search functions for trimmer capacitors by capacitance range, type of housing, adjustment type, vendor, and voltage rating.
Illinois Capacitor (www.illcap.com), with a website that allows engineers to search the company's extensive lines of capacitors by application, parameter, part number, or in comparison to a competitor's series of parts, specializes in large-valued capacitors for higher-power applications. Still, the company also offers the BCR series of ceramic disk capacitors with capacitance values from 1 to 680 pF and working voltage rating of 50 V for applications requiring stable performance with temperature.
Murata Electronics North America (www.murata.com) offers extensive lines of power and high-frequency capacitors, including the high-frequency ERA series of monolithic chip capacitors. These devices, which are available with fixed capacitances ranging from 0.5 to 1000 pF, incorporate nickel-barrier terminations for improved solderability. Designed for frequencies well above 1 GHz, they suffer capacitance drift of no greater than ±0.2 percent or ±0.05 pF (whichever is larger), even over an operating temperature range of –55 to +125ºC.
Voltronics Corp. (www.voltronicscorp.com), in the business of supplying high-quality trimmer capacitors since 1963, offers a wide range of trimmer capacitors including nonmagnetic components for medical applications. For example, the NMA4 series of nonmagnetic trimmers incorporate polytetrafloroethylene (PTFE) dielectric material to achieve DC working voltage ratings to 1000 V. Available in models covering minimum tuning ranges of 0.6 to 2.0 pF, 0.45 to 3.0 pF, and 0.6 to 5.0 pF, the trimmer capacitors feature minimum Qs of 3000 at 100 MHz.
The company also offers the classic A series of trimmer capacitors for applications not requiring nonmagnetic devices. The A series trimmers cover tuning ranges of 0.8 to 10.0 pF and 0.8 to 20.0 pF with impressive DC working voltage ratings of 2500 V. The A series trimmers exhibit a Q of 3000 when measured at 100 MHz and the device tuned to the maximum capacitance value.
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Johanson Manufacturing Corp. (www.johansonmfg.com) is another supplier of trimmer capacitors, with its 9350 series of ceramic chip trimmer capacitors. The single-turn capacitors, which are available with tuning ranges of 1.5 to 3.0 pF, 2 to 6 pF, 3 to 10 pF, 5 to 20 pF, and 8 to 30 pF, feature minimum Q of 500 at 1 MHz and working voltage ratings to 100 V.
In addition to several lines of surface-mount inductors, Sprague-Goodman Electronics (www.spraugegoodman.com) also supplies precision trimmer capacitors, such as the Pistoncap® line of microwave sapphire trimmer capacitors. Rated for 500 V, the trimmers are available for a variety of capacitance tuning ranges, including 0.3 to 1.2 pF, 0.4 to 2.5 pF, 0.6 to 4.5 pF, and 0.8 to 8.0 pF. The minimum Qs range from 1000 at 250 MHz for the highest-capacitance device to 4000 at 250 MHz for the lowest-valued trimmer. The company also offers multiturn PTFE-based trimmer capacitors with a capacitance range of 0.25 to 1.5 pF and voltage ratings as high as 1700 V. With minimum Q of 2000 at 1 MHz, these tiny trimmers provide the high stability needed in tuned filters and oscillators.
When searching for a capacitor or inductor, Panasonic Electromechanical Components Group (www.pansonic.com/industrial) has a useful feature that allows engineers to select an application topic, such as WLAN or GPS, and view a system-level block diagram of the application. By clicking inside the application block diagram, all applicable capacitors and inductors are listed (the firm also offers additional passive components for these applications, such as SAW filters). In addition, Spectrum Control (www.spectrumcontrol.com) and Metuchen Capacitors (www.metcaps.com) offer a variety of high-power multilayer ceramic capacitors for power suppliers and other power-control applications.
In contrast to capacitors, inductors store energy in a magnetic field, thus opposing changes in the flow of current. Inductors for RF and microwave applications are rated in units of nanoHenrys (nH) or microHenrys (µH) for more robust circuits and, similar to capacitors, are rated in terms of inductance tolerance, Q, DC resistance, voltage, current, and SRF. For example, the SMRF1010 series of surface-mount chip inductors from Gowanda Electronics (www.gowanda.com) covers an inductance range of 0.12 to 2.7 µH with minimum Q values of 30 at the lowest inductance and 24 at the highest inductance. The SRFs range from 750 MHz at the lowest inductance values to 77 MHz at the highest inductance values.
Coilcraft (www.coilcraft.com) recently announced its 0302CS series of inductors, with inductance values from 0.67 to 34.0 nH. With a 20-percent-smaller footprint than the company's 0402 series inductors, these 0805-size-packaged devices may well be the world's smallest wire-wound inductors. With 5-percent inductance tolerance for most values and SRFs exceeding 26 GHz at the lowest inductance values, these high-performance components exhibit Qs of typically 105 at 2.4 GHz for a 6-nH inductor and 102 at 2.4 GHz for a 16-nH inductor. In spite of the small size, the inductors handle generous amounts of current, with current-handling capability to 1.6 A.
The company's 0403HQ series of ceramic chip inductors exhibit Qs as high as 96 at 1.7 GHz. Available with inductance values from 1.9 to 18.0 nH, these high-current (to 2.2 A) inductors feature platinum/palladium/silver terminations for environmentally sensitive applications, and SRFs of 12 GHz and more at the lowest inductance values. The inductors are available with standard inductance tolerance of 5 percent.
Toko America (www.tokoam.com) offers the LLV0603F series of multilayer chip inductors with inductance values from 1 to 47 nH. The 0201 size inductors measure just 0.6 × 0.3 mm but are rated for current to 170 mA at the lowest inductance values. Units are available with inductance tolerance of ±0.3 nH or ±5 percent of the full inductance value. The SRFs reach 19 GHz at the lowest inductance values, while minimum Qs range from 11 to 23 over the range of inductance values.
Resistors carry a clearly descriptive name, since their function is to impede or control the flow of current through a circuit. Resistors, which are rated in units of ohms (often denoted by the Greek symbol Ω), are also characterized by their resistance tolerance, their temperature coefficient of resistance (TCR) or the amount of change in the resistance value as a function of temperature, the power rating at a given frequency, and their parasitic capacitance.
Barry Industries (www.barryind.com) offers the RP, RS, and RK series of engineering kits with resistor sizes ranging from 0302 to 2512, 0302 to 3725, and 0302 to 3725, respectively. Available with as many as 10 pieces each of 156 resistor values from 10 Ω to 27 MΩ in a single kit, the kits are available with resistance tolerances of 5 and 10 percent in package sizes ranging from 0.030 × 0.020 in. (0302) to 0.375 × 0.250 in. (3725).
Florida RF Labs (www.rflabs.com), which supplies surface-mount, tab, flange-mount, and chip resistors, offers the 81-8004B series of surface-mount resistors on a variety of substrate materials, including alumina, beryllium oxide (BeO), and aluminum nitride (AlN). These thin-film components can be specified with power ratings from 2 to 50 W at 4 GHz with resistance values from 5 to 400 Ω.
Gowanda Electronics (www.gowanda.com) recently introduced the SMRF series of surface-mount chip inductors with SRFs ranging from 22 to 750 MHz and inductance values ranging from 0.12 to 27 pH. The minimum Qs range from 22 to 30.
International Manufacturing Services (www.ims-resistors.com) offers both thin-film and thick-film resistors for high-frequency and power applications, including its RXI series of thick film on alumina resistors in sizes from 0201 to 2512 packages. Available with resistance values from 0.068 Ω to 22 MΩ, these thick-film chips feature a nickel barrier for improved solderability. They are available with resistance tolerances to ±0.5 percent and TCRs to ±50 PPM/ºC.
Due to the limited scope of this article, only a sampling of suppliers and their products have been mentioned here as examples. For a more complete listing of suppliers for capacitors, inductors, and resistors, please refer to the Microwaves & RF Product Data Directory, either in print or on-line at www.m-rf.com.