Configure the empirical value of the capacitor A good high-frequency decoupling capacitor can remove high-frequency components up to 1GHZ. Ceramic chip capacitors or multilayer ceramic capacitors have better high-frequency characteristics. When designing a printed circuit board, a decoupling capacitor must be added between the power supply and ground of each integrated circuit. The decoupling capacitor has two functions: on the one hand, it is the energy storage capacitor of the integrated circuit, which provides and absorbs the instantaneous charge and discharge energy of the integrated circuit; on the other hand, it bypasses the high-frequency noise of the device. The typical decoupling capacitor in a digital circuit is 0.1uf. The decoupling capacitor has a distributed inductance of 5nH. Its parallel resonance frequency is about 7MHz, which means that it has a good decoupling effect for noise below 10MHz. The noise has little effect. 1uf, 10uf capacitors, parallel resonance frequency above 20MHz, the effect of removing high frequency noise is better. It is often advantageous where a power supply enters the printed board and a 1uf or 10uf de-high-frequency capacitor is needed even for battery-powered systems. Every 10 or so integrated circuits need to add a charge and discharge capacitor, or storage capacitor, the capacitor size can be selected 10uf. It is best not to use electrolytic capacitors. The electrolytic capacitors are rolled up with two layers of membranes. This rolled structure acts as an inductance at high frequencies. It is best to use bile capacitors or polycarbonate capacitors. The selection of the decoupling capacitor value is not strict, and can be calculated as C = 1 / f; that is, 10MHz takes 0.1uf. No matter what power distribution scheme is used, the entire system will generate enough noise to cause problems, additional filtering measures are necessary. This task is accomplished by bypass capacitors. In general, a 1uf-10uf capacitor will be placed on the power input of the system, and a 0.01uf-0.1uf capacitor should be placed between the power pin and ground pin of each device on the board. The bypass capacitor is the filter. The large capacitor (approximately 10uf) placed on the power supply access port is used to filter the low frequency generated by the board (such as the line frequency of 60hz). The noise generated by the equipment working on the board will generate harmonics from 100mhz to higher frequencies. Bypass capacitors should be placed between each chip. These capacitors are relatively small, about 0.1u. General configuration principles of decoupling capacitors 1. 10 ~ 100uf electrolytic capacitor is connected across the power input. If possible, it is better to connect more than 100uf. 2. In principle, each integrated circuit chip should be equipped with a 0.01pf ceramic capacitor. If there is not enough space on the printed board, a capacitor of 1 ~ 10pf can be arranged every 4 ~ 8 chips. 3. For devices with weak anti-noise capability and large changes in power supply during shutdown, such as ram and rom storage devices, a decoupling capacitor should be directly inserted between the power supply line and ground of the chip. 4. Capacitor leads cannot be too long, especially high-frequency bypass capacitors cannot have leads. In addition, the following two points should be noted: a. When there are contactors, relays, buttons and other components in the printed board. When they are operated, a large spark discharge will occur, and the rc circuit shown in the figure must be used to absorb the discharge current. Generally r takes 1 ~ 2k, c takes 2.2 ~ 47uf. The input impedance of cmos is very high, and it is susceptible to induction, so when in use, the unused end should be grounded or connected to a positive power supply. Because most of the energy exchange is mainly concentrated on the power and ground pins of the device, these pins are independently connected directly to the ground plane. In this way, the voltage fluctuation is actually mainly caused by the unreasonable distribution of current. But the unreasonable distribution of current is mainly caused by a large number of vias and isolation bands. In this case, the voltage fluctuation will mainly transmit and affect the power and ground pins of the device. In order to reduce the voltage overshoot on the power supply of the integrated circuit chip, a decoupling capacitor should be added to the integrated circuit chip. This can effectively remove the influence of the burr on the power supply and reduce the radiation of the power supply loop on the printed board. When the decoupling capacitor is directly connected to the power supply leg of the integrated circuit instead of being connected to the power supply layer, its smoothing effect is best. This is why some device sockets have decoupling capacitors, and some devices require the decoupling capacitors to be sufficiently small from the device. The general principles of decoupling capacitor configuration are as follows: ◠A 10 ～ 100uF electrolytic capacitor is connected across the power input. If the position of the printed circuit board permits, the anti-interference effect of the electrolytic capacitor above 100uF will be better. ◠Configure a 0.01uF ceramic capacitor for each integrated circuit chip. If the printed circuit board space is too small to fit, you can configure a 1-10uF tantalum electrolytic capacitor every 4-10 chips. The high-frequency impedance of this device is particularly small, and the impedance is less than 1Ω in the range of 500kHz-20MHz And the leakage current is very small (below 0.5uA). For devices with weak noise capability and large current changes during shutdown and storage devices such as ROM and RAM, decoupling capacitors should be directly connected between the power supply line (Vcc) and ground (GND) of the chip. ◠The lead wire of the decoupling capacitor should not be too long, especially the high-frequency bypass capacitor must not have a lead wire. ◠When there are contactors, relays, buttons and other components in the printed board. When operating them, a large spark discharge will occur, and an RC circuit must be used to absorb the discharge current. Generally R takes 1 ~ 2K, C takes 2.2 ~ 47UF. ◠The input impedance of CMOS is very high, and it is susceptible to induction, so when using it, the unused end should be grounded or connected to a positive power supply. ◠Three types of decoupling capacitors for high frequency, low frequency, and intermediate frequency should be used in the design. The intermediate frequency and low frequency decoupling capacitors can be determined according to the power consumption of the device and the PCB. 47-1000uF and 470-3300uF can be selected respectively; P / V * V * F. ◠One decoupling capacitor for each integrated circuit. A small high-frequency bypass capacitor must be added to each electrolytic capacitor. ◠Use large-capacity tantalum capacitors or poly-cooling capacitors instead of electrolytic capacitors as circuit charge and discharge energy storage capacitors. When using tubular electricity, the housing should be grounded. Glass Premium Tempered,Heat Tempered Glass ,Exterior Oven Door Glass ,Microwave Oven Door Tempered Glass WCH Temper Glass Co., Ltd , https://www.temperglasswch.com