POWER & ENERGY EFFICIENCY HANDBOOK
Bringing science to the selection of mica capacitors for RF and microwave circuits An RF modeler makes it easy to predict in-circuit S-parameters for mica capacitors used at microwave frequencies.
The choice of capacitor can particularly impact the performance of circuits handling RF and microwave frequencies. Specifying passive components operating in this region can seem more like art than science. Fortunately, new online tools can help simplify the process. For no-fail circuits that must maintain their performance, there is no better dielectric choice than mica. Originally invented by Cornell Dubilier (CDE), mica capacitors offer important advantages over MLCCs and porcelain capacitors. These benefits include high Q, stability, and reliability.
MC Series mica chip capacitors.
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CDE — P&EE HB 10-19.indd 8
Sam G. Parler, Jr., P.E. | Cornell Dubilier
Capacitors with a mica dielectric have significantly higher Q than other capacitors partly because of ESR (equivalent series resistance) that is 10 to 20% lower. Lower ESR also leads to lower losses, less self-heating, and the ability to tolerate higher currents. Mica capacitors are incredibly stable over time, temperature, frequency, and voltage, proving consistent performance even with varying operating conditions. Because mica is a strong mineral, capacitors constructed with it aren’t prone to cracking. So mica capacitors handle higher voltages on larger chip sizes and work in applications subject to mechanical stresses that could destroy other capacitors. And mica capacitors tend to handle high-voltage spikes better than their ceramic counterparts. An online tool called the RF Mica Modeler provides an interactive console to assist in selecting the best mica capacitor within a capacitance range of 0.5 to 91,000 pF and voltage range of 100 to 4,000 V, targeting applications in the frequency range of 1 kHz to 4 GHz. The modeler charts estimates of the 10 • 2019
high-frequency electrical performance for three major classes of CDE circuitboard-mounted mica capacitors: leaded mica capacitors used in through-hole PCBs, surface-mounted metal case mica/ PTFE capacitors style MIN02 (5 X 5-mm footprint) and MCM01 (10×12 mm) for high current and high power-handling SMT mica chip capacitors in sizes 0805, 1210, 1812 and 2220. With one of the three package styles selected from the “Package Style” drop-down box, the “CDE Part Number” selection box lists standard catalog part numbers ranked by their capacitance value. Selecting a part number brings up an outline drawing and the physical dimensions. Also appearing is blue “CATALOG” text that is context sensitive. It will open a new tab in your browser with the datasheets for the selected package style (leaded, chip, metal case). The tool can model the S-parameters for the capacitor mounted on a test circuit transmission line, in either series or shunt (parallel) configuration, chosen in the dropdown box in the lower left of the modeler. The tool plots the capacitor’s eeworldonline.com | designworldonline.com
10/10/19 8:34 AM
