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Single Layer Capacitor for Microwave Application
2020/12/10 03:12:53

Single layer capacitor (SLC) are widely used in microwave/optical transmitter, TOSA/ROSA/BOSA (transmitting/receiving/bidirectional optical component), synthesizer, oscillator and other signal generator due to their characteristics of DC blocking, high frequency bypass or impedance matching. In all of these applications, choosing the right capacitor is the first step to get the desired performance. The capacitance of a single layer capacitor can be calculated based on the parallel-plate capacitor equation:


Among them, C is the capacitor, the unit is Farah (F); A is the area where the two plates overlap, the unit is square meter (m2), εr is dielectric constant; ε0 is the electric constant (εr≈8.854×10-12F/m) ; d is the spacing between the parallel plates, the unit is meter (m).

In an ideal capacitor, there is no resistance or inductance, so the impedance decreases inversely with the frequency. However, when the frequency reaches the self-resonant frequency (SRF), the impedance is minimized, and then the inductance dominates and the impedance increases with the frequency. Another thing to note is that single layer capacitor has less impedance near the self-resonant frequency than an ideal capacitor. This is due to the ideal capacitor does not have an equivalent series inductance (ESL) or equivalent series resistance (ESR), but the equivalent series inductance of a single layer capacitor cancels out the capacitive reactance (thus cancels out the impedance) near the self-resonant frequency. This means that near the self-resonant frequency, a single layer capacitor has less loss than an ideal capacitor.

Other parameters, including the rated working voltage (RWV), insulation resistance (IR) of capacitor, are directly related to the thickness of the dielectric. Capacitor varies with the bias voltage, which in turn deteriorates with the increase in dielectric constant, and capacitor changes with temperature, which in turn varies with specific dielectric materials.

In general, the following principles can be followed when selecting a single layer capacitor:

First, in order to obtain the best equivalent series resistance, choose a large and thin single layer capacitor.

Second, in order to obtain the best rated working voltage and insulation resistance, choose a thicker single layer capacitor.

Third, for the highest self-resonant frequency, choose a smaller, thinner single layer capacitor.

Fourth, for the minimum loss, use the minimum dielectric constant.

Single layer capacitor produced by EXSENSE Electronics Technology Co., Ltd., has the characteristics of small size (minimum can be up to 0.23mm), thin thickness (thinnest can be up to 0.12mm), low equivalent series resistance, low loss, which is able to play a role in DC blocking, RF bypass, smoothing, tuning in microwave application.

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