Glossary of Capacitor Terms

Bypass capacitor – A circuit configuration wherein a capacitor selectively prevents high-frequency signals from propagating to one part of a circuit from another.  Generally, the capacitor connects a circuit component to ground, thereby allowing a range of (typically) RF frequency signals to pass but blocking DC.  May also be used to minimize noise entering the system.

Capacitance – A unit of measure describing the electrical charge storage of a device (in coulombs) relative to the voltage across its terminals. Capacitance is measured in farads (1 Farad = 1 Coulomb/Volt), microFarads (millionths of a Farad), nanoFarads (billionths of a farad or 10-9), or in picoFarads (trillionths of a Farad or 10-12).

DC Blocks – A circuit configuration wherein a capacitor connects a circuit component to other circuit components, thereby allowing a range of RF frequency signals to be further processed but blocking DC. Typically used between stages of a circuit, where DC is injected to bias one active component, but needs to be prevented from biasing another, or appearing across (typically 50-Ohm) input or output load resistances. 

Decoupling Capacitor – another name for a bypass capacitor. 

DWV – The Dielectric Withstanding Voltage of a capacitor is a DC voltage, typically, 250 percent of the rated voltage, that the component will sustain for at least five seconds and not incur any damage.  

ESR – Equivalent Series Resistance is the resistive component of an unmounted capacitor’s equivalent circuit – a capacitor, resistor, and inductor, all in series. The ESR of a ceramic capacitor changes with frequency because of changing ceramic and metallic losses within the component.   

FSR – First Series Resonance (FSR) is defined as the lowest frequency at which the imaginary part of a capacitor’s input impedance, Im(Zin), equals zero.  Should Im(Zin) or the real part of the input impedance, Red(Zin), not be monotonic with frequency at frequencies lower than those at which Im(Zin) = 0, the FSR shall be considered as undefined.  FSR is dependent on substrate thickness and dielectric constant; on capacitor orientation; and on mounting pad dimensions.

High-Q ceramic Capacitors -see for details  https://passiveplus.com/products/fixed-capacitors/hi-q-low-esr-capacitors/

IR – The Insulation Resistance of a capacitor is the resistance between its terminals, measured at DC at its rated voltage.  The measurement is sensitive to ambient humidity, as well as surface cleanliness and, performed correctly, is a metric of ceramic quality.   

MTTF – Mean Time to Failure.  MTTF is the average time a component remains in operation until it needs to be replaced. 

Q factor – The Q factor of a capacitor, also known as the Quality factor is the ratio of the capacitor’s reactance to its resistance at a given frequency. It is the reciprocal of the Dissipation Factor.  

Single Layer Capacitor – two plates separated by a dielectric.  For more information, see https://passiveplus.com/products/fixed-capacitors/single-layer-capacitors/

Smith Chart – a chart that shows reflection magnitude and phase.  Points on the chart can be read as real and imaginary parts of impedance or admittance.

SWaP- Critical concerns when designing components or subsystems for RF Microwave applications – Size, weight, and power (SWaP)

TCC – Temperature Coefficient of Capacitance.  A measure and specification of the maximum change of capacitance with temperature, over a particular range of the latter. It is usually given in either parts-per-million per degree Centigrade, ppm/0C, or simply as a percentage.  Examples are: NP0 (±30 ppm/0C, -55 to +125 0C), X7R (±15%, -55 to +125 0C ), and X5R ((±15%, -55 to +85 0C) .

Variable Capacitors – A Variable Capacitor, also known as a Trimmer Capacitor, is a unit designed for fine adjustments or calibration in RF Circuits. These components enable precise tuning and optimization of electronic circuits.  See Understanding Trimmer Capacitors for more information.

VCC – The Voltage Coefficient of Capacitance is the ratio of capacitance values at different applied DC voltages.  

Voltage Breakdown – The voltage breakdown of a capacitor [DC and RF] is that applied voltage (DC or RF peak) that causes a specified current to flow.  It can manifest in a number of ways, e.g., arc-over in the air, corona near one terminal, “creep” between terminals, internal arcs between electrodes, or internal arcs between electrodes and terminations.  It often – but not always – results in permanent destruction of the device.

WVDC – The Working Voltage DC, otherwise known as the “rated voltage” is, generally, the DC voltage a capacitor can be continuously exposed to and not have its principal specifications (e.g., capacitance, dissipation factor, insulation resistance) change by more than particular specified amounts over a specified time period.  Certain capacitors, typically Broadband units with X7R or X5R TCCs, may have an additional constraint: that, at their WVDCs, their capacitance remains at or above a specified value.