Capacitance is the most common used device in the circuit design, is one of the passive components, active device, in a nutshell is the need to (
The source device is called active device, can need not (
The source device is passive components.
Capacitance is also often play an important role in the high speed circuit.
Function and purpose of capacitance, generally have a good variety.
Such as: in bypass, lotus root, filter and energy storage of the role of;
To analyze in detail below: 1, the dc insulation: the role is to prevent dc through and through communication.
2, the bypass (
: for some components in parallel to provide low impedance in ac circuit pathways.
s: bypass capacitors, also known as the decoupling capacitor, is for a device that provides energy storage device, which USES the frequency impedance characteristic of the capacitor (
Ideal on frequency increases, the frequency features of capacitance impedance reduced)
Try to close to the load device in the bypass capacitor power supply pin and pin, the impedance requirement, it is important to note that when drawing PCB only when close to a certain components to suppress voltage or other lose signal caused by too much higher potential and noise, namely the ac component of dc power supply, through capacitive coupling to the power supply, have played an important role in purifying dc power supply.
When it is shown in figure C1 for bypass capacitors, drawing close to IC1 figure C1 decoupled capacitive: decoupling capacitor, is the interference of output signal as the filter object, decoupling capacitor is equal to the battery, use its charge and discharge, make the signal after amplification will not disturbed by current mutation.
Its capacity according to the frequency of the signal, the degree of inhibition of corrugated, decoupled capacitance is play the role of a 'battery', meet the changes of driving circuit current, avoid mutual coupling interference.
Bypass capacitors actually also to coupling, just bypass capacitors generally refers to the high frequency bypass, the switch is the high frequency noise increase a low impedance leakage prevention way.
High-frequency bypass capacitors tend to be small, according to the resonant frequency is generally take 0.
1 f, 0。
01 f, etc. ;
And the capacity of the coupling capacitance, generally larger, could be 10 f or greater, based on the distributed parameter in the circuit, and the change of the drive current to determine the size.
Figure as shown in figure C3 for its decoupling capacitor C3 the difference: the bypass is the input signal as object of filter, the interference and decoupling is the interference of output signal as the filtering out objects, prevent jamming signal returned to power.
4, filter: this is very important for circuit, the capacitor behind the CPU is the basic function.
The frequency f, the greater the capacitance impedance Z is smaller.
When high frequency capacitance C due to impedance Z is very small, equivalent to the high frequency noise short circuit to GND.
Filtering effect: ideal capacitance, the greater the capacitance, impedance is smaller, by the higher the frequency also.
Electrolytic capacitors are generally not more than 1 f, the inductive component is very big, so after high frequency impedance will instead.
Analysis: because of the timing capacitor capacity determines the oscillation frequency of the line oscillator, so the request timing capacitor capacity is very stable, not changes over environment humidity, line so that the oscillation frequency of the oscillator is stable.
When work at higher temperatures, the capacity of the Cl in the increase, and C2 in reducing capacity, two capacitors in parallel after the sum of the total capacity of two capacitance, due to an increase in capacity and another in reduced, so the total capacity basically remain unchanged.
Similarly, in the temperature falls, the decrease of the capacity of a capacitor in another increase in the total capacity, stable oscillation frequency, to realize temperature compensation.
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