Part I: Classification of capacitor
In the design of the circuit capacitance classification from the application, the capacitance can be divided into four categories:
The first category: AC coupling capacitors. Mainly used in AC-coupled Ghz signal.
The second category: decoupling capacitors. Mainly used to filter out high-speed circuit board to maintain power or ground noise.
The third category: active or passive RC filter or frequency selective network used in capacitors.
The fourth category: analog integrator and sample and hold circuit used in capacitors.
In this article we will discuss the second largest category of decoupling capacitors.
Capacitance from manufacturing materials and processes for classification, mainly in the following different forms of capacitance:
1, NPO ceramic capacitors
2, polystyrene capacitors pottery
3, polypropylene capacitors
4, Teflon capacitors
5, MOS capacitor
6, polycarbonate capacitors
7, polyester capacitors
8, monolithic ceramic capacitors
9, mica capacitors
10, electrolytic capacitors
11, tantalum electrolytic capacitor
In the actual design of the reasons due to the price, procurement and other areas often use capacitors are: ceramic capacitors, electrolytic capacitors, tantalum capacitors.
Part II: Specific models and distributed parameter capacitance
To properly use reasonable capacitance capacitors need to recognize the specific nature and role of the specific meaning of each model and the model distribution parameters. And other components, the actual capacitance of the "ideal" capacitor type, the "real" capacitor due to its packaging, materials, etc., which is equipped with an additional characteristic of the inductor, resistor, must be additional "parasitic "element or" non-ideal "to characterize the performance, their performance in the form of a resistance element and the inductance element, and a non-linear dielectric storage performance. "Real" capacitor model is shown below. Due to the nature of these parasitic elements capacitor decisions, usually have a detailed description of the capacitor manufacturer's product description. Understanding these parasitic effects in each application will help you choose the right type of capacitor.
Capacitance should actually consists of six parts. In addition to its own capacitor C, there are the following components:
An equivalent series resistance ESR RESR: capacitor equivalent series resistance is determined by the resistor capacitor pin and two plates of a capacitor in series constitute the equivalent resistance. When a large alternating current through the capacitor, RESR capacitor energy consumption (resulting loss). It contains the RF circuitry and high ripple current power supply decoupling capacitors will cause serious consequences. But for precision high impedance, small-signal analog circuit does not have a great impact. RESR lowest capacitors are mica capacitors and film capacitors.
2, the equivalent series inductance ESL, LESL: capacitor equivalent series inductance capacitor pin inductance by two plates of the capacitor equivalent series inductance formed. Like RESR Like, LESL also a serious problem in the radio frequency or high frequency operation, although the precise circuit itself is working properly at DC or low frequency conditions. The reason is that the case for precision analog circuit transistor transition frequency (transition frequencies) expanded to several hundred megahertz or gigahertz, and still has a gain, low inductance values can zoom resonance signal. This is the case of the high frequency power supply terminal of this circuit suitable to be the main reason for the decoupling.
3, the equivalent parallel resistance EPR RL: what we usually refer to the capacitor leakage resistance, AC-coupled applications, storage applications (such as analog integrator and sample holder) and when the capacitor is used in high-impedance circuits, RL is a important parameters should ideally only the capacitor charge current changes with the external. However, the actual RL of the charge in the capacitor at a rate determined by the RC time constant of the slow leak.
4, or two parameters RDA, CDA is also distributed capacitance parameters, but the actual impact should be relatively small, not presented here. Therefore, the capacitor has three important distribution parameters: ESR, ESL, EPR. One of the most important is the ESR, ESL, actual capacitance model analysis is generally used when the RLC simplified model, the analysis of the capacitor C, ESR, ESL, a simplified model which we will make the analysis focused on the capacitor week.
5, here we introduce a detailed model, based on the design is often used to talk about our two kinds of capacitors:
6, electrolytic capacitor (example: tantalum and aluminum capacitors) of large capacity, low resistance due to its isolation, is the equivalent parallel resistance EPR is small, so the leakage current is very large (typically 5 ~ 20nA/μF), thus It is not suitable for storage and coupling. Electrolytic capacitor is suitable for power supply bypass capacitors for the power supply stable power supply. Best suited for AC coupling and the charge storage capacitor is Teflon capacitors and other polyester type (polypropylene, polystyrene, etc.) capacitors.
7, monolithic ceramic capacitors, more suitable for high frequency decoupling capacitor circuits, because they have very low equivalent series inductance is the equivalent series inductance (ESL) is very small, have had a very wide band decoupling. This constitutes a great structural his relationship monolithic ceramic capacitor is composed of a metal thin film and a multilayer laminated film composed of a ceramic, and a multilayer film according to the parallel arrangement of the bus, instead of a serial manner in accordance with the winding The.
8, this week we talked about the details of the equivalent capacitance model, I believe we now have a relatively deep capacitor should know, next week we will continue to talk, we actually often used to analyze the application of simplified equivalent capacitance model, and his origin and meaning of the impedance curve.
Part III: capacitance and impedance curves simplified model
To facilitate analysis, the actual analysis should always be used by the equivalent series resistance ESR, equivalent series inductance ESL, RLC model of a capacitor thereof. Because the effect on the frequency characteristics of capacitance is the largest ESR and ESL.
