How to Judge the Acceptance of PCB Quality
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Method to Solve the Noise Interference of Power Supply on High-frequency PCB Board
Disassembly Skills of Chip Components on PCB
What Factors Should Be Considered in the Selection of High-frequency PCB CCL
How to Place Special Components during PCB Layout
What Are the Functions of Capacitors in Circuits?
Testing Techniques for Common Electronics Components
What to do if There is a Short Circuit on the PCB
Desoldering Principles and knowhow during PCBA Processing
Black Oxidation of the Inner Layer of the Multilayer PCB
How to Ensure the High-performance Design of PCB
What Is the Printing Process of SMT Solder Paste?
PCB without fiducial mark, Is There Any Way to do SMT for It
What Are the Benefits of Reserving Break-up Tab for PCB Production
How Does SMT Affect PCB Production Time and Speed It Up
Classification of PCBs from three aspects
Common Problems and Solutions for Dry Film pasting during PCB Manufacturing process
Several Elements to Inspect after PCB Design
What is a halogen-free circuit board?
What Do Capacitive Coupling and Decoupling Mean?
What Are the Differences Between PCB Paste Mask and Solder Mask?
How PCBA Is Packaged and Shipped
How long can PCBA finished products be stored?
What Are the Differences and Relations Between PCB, PCBA, and SMT?
PCB Baking Specifications
PCB "Solder Mask Tenting" and "Solder Mask Opening"
Five reasons for PCB deformation and six solutions
Importance of first article inspection of PCBA board
Temperature zone standard for SMT reflow soldering
Small and medium volume PCB manufacturers in China
The main reason for PCBA cleaning
For power filter, the more capacitors, the better?
What does PCBA programming mean?
Content of PCB incoming testing
What conditions must be met for PCB circuit board soldering?
What is Blind via and Buried via
PCBA Manufacturers Temperature and Humidity Sensitive Components Management
Why choose Shenzhen SMT processing factory?
How long does it take to calculate the quotation for PCBA manufacturing?
Introduction of PCB design clearance requirements
Explanation of BOM, DIP, SMT, SMD
Introduction of the process of PCBA prototype
How to prevent pseudo soldering or cold soldering defects in PCBA manufacturing?
Factors that affect the Price of FPCB
What information is required for SMT processing at PCBA factory?
Skills of using 0ohm resistor in PCB design
How to select a PCBA manufacturer
SMT processing solder joint quality inspection
Characteristics difference between immersion gold PCB and gold plating PCB
Common malfunctions of Circuit Board Caused by Moisture
A Few Rules about PCB Panelization
Compare of multi-layer PCB with single/double layer PCB
Why do we need to introduce so many subdivided GND
Difference between immersion gold boards and gold plating boards
Aluminum PCB structure
Classification of different GND in circuit
Why PCB baking is necessary during manufacturing process
The handle and precautions of OSP board in SMT process
How to choose capacitors for filter decoupling
How to choose filter capacitor for switching power supply
5 database need for SMT process
Function of three-terminal capacitor
Introduction of PCB OSP surface treatment
Method of inspecting the quality of SMT by step
How to find the short point between VCC and GND
Difference between 850nm and 940nm infrared LED
Component layout of PCB SMT DFM
Pad shape influence on the strength and reliability of the soldering joints
The difference between high temperature solder paste and low temperature solder paste
Introduction to manual welding processing
Manual visual inspection in PCBA processing
Characteristics of the conformal coating process
Difference between hardware engineers and software engineers
PCBA processing operation rules
China PCB upstream materials has continued to soar
Difference between serial buses and parallel buses
The key points of quality control in PCBA processing
Common causes of solder beading during SMT process
Analysis of the advantages and disadvantages of HASL PCB surface
Requirements for layout of components during SMT assembly
Selection of electronic components and CCL for PCBA
Performance and appearance quality inspection of components.
Quality and Reliability of SMT Chip Processing and Production
Coupling and decoupling function of capacitor
Two methods to connect digital ground and analog ground
Common sense in SMT process

How to choose capacitors for filter decoupling

What is filter decoupling? Simply put, it stores energy when the chip does not need current, and replenish energy in time chip when needs current.

You may think that this responsibility is for DCDC or LDO? Yes, they can be done at low frequencies, but high-speed digital systems are different.

Let's take a look at the capacitor first. The function of the capacitor is simply to store charge. We all know that a capacitor should be added to the power supply to filter, and a 0.1uF capacitor is placed on the power supply pin of each chip to decouple.

Why the capacitors next to the power pins of some board chips are 0.1uF or 0.01uF. Is there anything to pay attention to?
To understand this, it is necessary to understand the actual characteristics of the capacitor. The ideal capacitor is just a storage of energy, that is, C.
The actual manufactured capacitors are not so simple. When analyzing power integrity, the commonly used capacitor models are shown in the figure below.

In the figure, ESR is the series equivalent resistance of the capacitor, ESL is the series equivalent inductance of the capacitor, and C is the real ideal capacitor.
ESR and ESL are determined by the manufacturing process and materials of the capacitor and cannot be eliminated. What impact will these two things have on the circuit?

ESR affects the ripple of the power supply, and ESL affects the filter frequency characteristics of the capacitor.
We know that the capacitive reactance of the capacitor Zc=1/ωC, the inductive reactance of the inductor Zl=ωL, (ω=2πf), the complex impedance of the actual capacitor is Z=ESR+jωL-1/jωC=ESR+j2πfL-1/j2πfC.

It can be seen that when the frequency is very low, the capacitor works, and when the frequency is high, the effect of the inductance cannot be ignored. When the frequency is higher, the inductance takes the leading role and the capacitor loses its filtering effect.
So remember, the capacitor is not a simple capacitor at high frequency. The filter curve of the actual capacitor is shown in the figure below:

As mentioned above, the equivalent series inductance of the capacitor is determined by the manufacturing process and material of the capacitor. The ESL of the actual SMD ceramic capacitor ranges from a few tenths of nH to a few nH. The smaller the package, the smaller the ESL.

From the filter curve of the capacitor above, we can also see that it is not flat. It is like a 'V', which means that it has frequency selection characteristics. Sometimes, we hope that it is as flat as possible (previous board-level filtering), sometimes it is hoped that the sharper the better (filtering or notching).

What affects this characteristic is the quality factor Q of the capacitor, Q=1/ωCESR. The larger the ESR, the smaller the Q and the flatter the curve. On the contrary, the smaller the ESR, the larger the Q and the sharper the curve.

Usually tantalum capacitors and aluminum electrolysis capacitors have relatively small ESL, but large ESR, so tantalum capacitors and aluminum electrolysis have a wide effective frequency range, which is very suitable for the board level filtering for power supply.

That is, in the input stage of DCDC or LDO, a larger capacity tantalum capacitor is often used for filtering.

And put some 10uF and 0.1uF capacitors close to the chip for decoupling, ceramic capacitors have very low ESR. Whether we put 0.1uF or 0.01uF close to the pins of the chip, the following are listed for your reference:

Frequency Hz

Capacitor selection


10uF or above tantalum/ aluminum capacitors


100nF(0.1uF) ceramic capacitors


10nF(0.01uF) ceramic capacitors


1nF(0.001uF) ceramic capacitors

So, don't put 0.1uF capacitors in every circuit in the future. In some high-speed systems, these 0.1uF capacitors won't work at all.