The Chinese name for PCB is printed circuit boards because they are manufactured through electronic printing, hence the term “printed” circuit board. China’s PCB board development began in 1956, and between 1963 and 1978, it gradually expanded to establish the PCB board industry. Over 20 years after economic reforms began, the industry saw rapid growth thanks to the introduction of advanced foreign technology and equipment. Single-sided, double-sided, and multi-layer boards developed swiftly, and the domestic PCB board industry grew from small to large scale.

By 2002, China became the world’s third largest producer of PCB boards. In 2003, the output value and import-export volume of PCB boards exceeded 6 billion US dollars, making China the second largest producer globally. The industry has maintained rapid growth of about 20% in recent years, and it is expected to surpass Japan around 2010 in both PCB board output value and technological development.

Capacitance (or capacitance) is a physical quantity that characterizes a capacitor’s ability to store charge. It represents the amount of electric charge required to increase the potential difference between the capacitor’s two plates by 1 volt. Physically, a capacitor serves as a static charge storage device (akin to a bucket for holding charge), and it finds essential applications in electronics and electrical circuits. Capacitors are crucial for power supply filtering, signal filtering, signal coupling, resonance, DC blocking, and other circuit functionalities.

1. The classification of capacitors

Capacitors are classified by application in circuit design, and can be divided into four categories:

1) AC coupling capacitors: Mainly used for AC coupling of GHz signals.

2) Decoupling capacitors: Mainly used to filter out noise from the power supply or ground of high-speed circuit boards.

3) Capacitors used in active or passive RC filtering or frequency selection networks.

4) Capacitors used in analog integrators and sample-and-hold circuits.

In this article, we will focus on the second type: decoupling capacitors.

Capacitors are also classified based on the materials and manufacturing processes, primarily into the following types:

1.1 NPO Ceramic Capacitors

1.2 Polystyrene Ceramic Capacitors

1.3 Polypropylene Capacitors

1.4 PTFE Capacitors

1.5 MOS Capacitors

1.6 Polycarbonate Capacitors

1.7 Mylar Capacitors

1.8 Monolithic Ceramic Capacitors

1.9 Mica Capacitors

1.10 Aluminum Electrolytic Capacitors

1.11 Tantalum Electrolytic Capacitors

2. The specific model and distribution parameters of capacitance

To properly and effectively apply capacitors, it is crucial to understand their specific models and the meaning and function of each distribution parameter within the model. Like other components, real capacitors differ from ideal capacitors in that they exhibit additional characteristics such as inductance and resistance due to packaging and materials. These necessitate the consideration of additional “parasitic” components or non-ideal properties, including resistive and inductive elements, nonlinearity, and dielectric memory.

From the diagram above, we observe that a capacitor effectively comprises six components. Apart from its capacitance (C), it includes:

2.1 Equivalent series resistance (ESR): ESR is the sum of the pin resistance and the equivalent resistance of the capacitor plates in series. ESR causes energy dissipation and losses when large AC currents flow through the capacitor, which can significantly impact RF circuits and decoupling capacitors in power supplies. However, its effect on high-impedance, small-signal analog circuits is minimal. Capacitors with high ESR typically include mica and film capacitors.

2.2 Equivalent series inductance (ESL): ESL consists of the pin inductance and the equivalent inductance of the capacitor plates in series. Like ESR, ESL can pose issues in RF or high-frequency applications, while being less impactful on precision circuits operating at DC or low frequencies. This is due to transistors in precision analog circuits amplifying resonant signals with very low inductance values.

2.3 Equivalent parallel resistance (EPR): Commonly known as capacitor leakage resistance, RL is critical in AC-coupled applications and storage scenarios like analog integrators and sample-and-holds. RL causes charge leakage at a rate determined by the RC time constant, differing from the ideal capacitor where charge should vary only with external current.

2.4 Parameters RDA and CDA are also capacitance distribution parameters but have relatively minor influences in practical applications and are thus not detailed here.

Therefore, the three significant distribution parameters of capacitance are ESR, ESL, and EPR, with ESR and ESL being the most crucial. Typically, the analysis of capacitor models simplifies to the RLC model.

2.5 Now, based on the detailed model introduction, let’s discuss two commonly used capacitors in our designs.

2.6 Electrolytic capacitors (such as tantalum and aluminum electrolytic capacitors) possess large capacitances but low insulation resistance, resulting in very small equivalent parallel resistance (EPR) and consequently high leakage currents (typically 5~20nA/μF). As a result, they are unsuitable for storage and coupling applications, but are ideal for stabilizing power supplies as bypass capacitors.

2.7 Monolithic ceramic capacitors are suitable for high-frequency decoupling in circuits due to their low ESL (equivalent series inductance), which broadens their decoupling frequency band. This characteristic stems from their structural composition, which includes multiple layers of interlayer metal films and ceramic films arranged in parallel with bus bars rather than wound in series.

2.8 This concludes our discussion on the detailed equivalent models of capacitors. With this information, it is expected that readers now have a thorough understanding of capacitors. We will continue next week by analyzing simplified equivalent models of capacitors commonly used in applications, as well as examining the origin and significance of their impedance curves.

3. Simplified model of capacitance and impedance curve

For analytical convenience, the RLC model—comprising series equivalent resistance (ESR), series equivalent inductance (ESL), and capacitance—is often employed.