【 Weak current College 】 decoupling capacitor and bypass capacitor difference 】

Bypass capacitance is not a theoretical concept, but a practical method for regular use, 50-60 's, the Word also has its own meaning, is now no more.

Tubes or transistors is bias, is to determine the working point of DC power supply condition. For example, the tube of the grid as opposed to cathode often requires Canada to have the negative pressure, to a DC power supply, as a cathode resistor to ground threaded, use plate flow forming cathode-to-ground are potential and gate DC ground, this bias technology called a "partial", but for (AC) signal, it also is a negative feedback, in order to eliminate this effect, in this resistance on parallel a large enough capacity, this point is called bypass capacitor. Then there's information to extend the use in similar circumstances.

Decoupling capacitor in IC VDD serves two purposes: one is the integrated energy storage capacitors, on the other hand bypass the devices off high frequency noise.

Digital circuit in typical decoupling capacitor value than 0 μ F. The capacitor inductance of typical values are 5 μ H. Than 0 μ F of decoupling capacitor has 5 μ H of inductance, its parallel resonance frequency around about 7MHz, that is, for the noise 10MHz following good decoupling effect more than the 40MHz noise has little to no effect. 1 μ F, 10 μ F capacitor, parallel resonance frequency in 20MHz above, removing the effect of high frequency noise is better. Approximately every 10 tablets to an integrated circuit charge-discharge capacitor, or 1-capacitor, optional 10 μ F. The best no electrolytic capacitors, electrolytic capacitors is a two-layer film volume, this volume looks at the structure in the high-frequency performance for the inductor. To use the tantalum capacitor or polycarbonate capacitors. Decoupling capacitor selection is not strictly, C = 1/F, than 0 μ F 10MHz fetch, fetch 0.01 μ F 100MHz.

In General, the capacity for uf-capacitance, like Electrolytic Capacitor or tantalum capacitor, the greater his inductance, the resonant frequency of smaller, low-frequency signal through the better, and the high-frequency signal, showing strong inductive, impedance, at the same time, large capacitance can also play the role of local charge pool, you can reduce the power of local interference through; coupled out to 0.001 ~ 0.1uf of capacitors, ceramic capacitors for General or MICA capacitors, inductors, the resonant frequency is high, the impedance of the high-frequency signal is relatively small, you can provide for high-frequency interference signal a bypass, reducing the coupling interference of the local

Bypass is to the fore or power portable high-frequency noise or signal filtering; to Lotus is to make sure that the output of the stable output (mainly against diodes work) and "small reservoirs", in other large current work guaranteed power fluctuation will not affect the work of the circuit; add that is the so-called coupled: is passed between the pre-amp signal but not interact with all levels of static working point of a symbol

Active devices in the switch from high-frequency switching noise will spread along the power cord. Decoupling capacitor's main function is to provide a local DC power to active devices to reduce switching noise in communication and on the Board will be guided to the noise.

Filter capacitors in power rectifier circuit, used to filter out the communication components. The output of the DC smoother.

Decoupling capacitor available in the amplifier circuit is not needed to talk, to eliminate the self-excited, make amplification and stable work.

Bypass capacitors used in connection with resistance, resistance to both ends by AC signal.

1. on the decoupling capacitor energy storage of understanding

1) decoupling capacitor is removing high frequency interference such as RF signal, interference into by electromagnetic radiation.

In fact, the chip is also nearby capacitor energy storage function, the second digit.

You can put the total power as the Miyun reservoir, our building families need water, this time, the water is not direct from the reservoir so that the distance is too far away, such as water, we have the thirsty. Actual water from the top of the Tower of the building, the water tower is actually a
The role of a buffer.

If the micro-level, high-frequency devices at work, its current is not contiguous, and frequency is very high, and the devices VCC to total power for some distance, even if the distances are long, the frequency is high, the impedance Z = I * wL + R, line effects of inductance can be very large, will guide

-Devices in need current, can not be timely supply.

While decoupling capacitor can compensate for this deficiency.

This is why many circuit board in the high-frequency devices VCC pins by placing one of the reasons why small capacitor

(Usually in the VCC pin a decoupled capacitor in parallel so that Exchange components from the capacitor to ground. ）

2) active devices in the switch from high-frequency switching noise will spread along the power cord. Decoupling capacitor's main function is to provide

A local DC power to active devices to reduce switching noise in communication and on the Board will be guided to the ground noise

2. bypass capacitor and the difference between a decoupling capacitor

Decoupling: removal of the device when you switch from high-frequency devices into the distribution network of RF energy. Decoupling capacitor can for the device for the localization of DC voltage source, it reduces cross-plate surge current particularly useful.

Bypass: from the component or cable transfer out of common RF energy. This primarily by producing AC bypass eliminate unintended energy into the sensitive part, moreover can also provide baseband filtering function (bandwidth restricted).

We often see that the power supplyand ground connection between a decoupling capacitor, it has three aspects: first, as the capacitor energy storage integrated circuits; the second is to filter out the high frequency noise generated by the device, cutting off its spread through power supply circuits; threeTo prevent power portable noise interference on the circuit.

In electronic circuits, and decoupling capacitor and bypass capacitors are played the role of anti-interference, capacitance where it is placed, salutation won't be the same. For the same circuit, bypass (bypass) capacitor is the input signals in high frequency noise as a filter object, the former grade portable high-frequency noise filtering, and decoupling capacitors (decoupling), also known as decoupling capacitor to the output signal interference as filtering objects.