Do you know how to rectify capacitor?
First of all, the product should be diagnosed according to the actual situation, and the routes and ways of interference sources and their mutual interference should be analyzed. According to the analysis results, the targeted rectification is carried out.
In general, the main methods of rectification are as follows：
1. Attenuating the interference source. On the basis of finding the interference source, the interference source can be weakened within the allowable range. The method of weakening the source generally has the following methods:
a. Add a decoupling capacitor between the Vcc and GND of the IC. The capacitance of the capacitor is between 0.01μF and 0.1μF. Pay attention to the lead of the capacitor when installing, so that the shorter the better.
b. Add an attenuator while ensuring sensitivity and signal to noise ratio. For example, the crystal oscillator in VCD and DVD disc players has a serious impact on electromagnetic compatibility. It is one of the feasible methods to reduce the amplitude, but it is not the only solution.
c. Another indirect method is to keep the signal line away from the interference source.
2, the classification of wire and cable in electronic equipment, line-to-line coupling is an important way, but also an important cause of interference, because the frequency factor can be roughly divided into high-frequency coupling and low-frequency coupling. Due to the different coupling methods, the method of rectification is different, and the following are discussed separately:
(1) Low-frequency coupling is a case where the length of the guide line is equal to or smaller than 1/16 wavelength, and the low-frequency coupling can be divided into electric field and magnetic field coupling.
The physical model of electric field coupling is capacitive coupling, so the main purpose of rectification is to reduce the distributed coupling capacitance or reduce the coupling amount. The following methods can be used:
a. Increasing the circuit pitch is the most effective way to reduce the distributed capacitance.
b. Add a highly conductive shield and make the shield a single point ground to effectively suppress low frequency electric field interference.
c. An additional filter can reduce the amount of coupling between the two circuits.
d. Reduce the input impedance. For example, the input impedance of the CMOS circuit is very high, and it is extremely sensitive to electric field interference. A capacitor or a resistor with a lower resistance can be connected to the input terminal within the allowable range.
The physical model of magnetic field coupling is inductive coupling, and its coupling is mainly coupled by the mutual inductance between the lines. Therefore, the main method of rectification is to destroy or reduce the coupling amount. Generally, the following methods can be used:
a. Add a filter. Pay attention to the input and output impedance of the filter and its frequency response when adding the filter.
b. Reduce the loop area between the sensitive loop and the source loop, that is, try to make the signal line or the current-carrying line close or twist together with its return line.
c. Increase the spacing between the two circuits to reduce the mutual inductance between the lines to reduce the amount of coupling.
d. If possible, try to reduce the coupling between the two circuits by making the sensitive loop and the source loop plane orthogonal or nearly orthogonal.
E.Using high-magnetic materials to wrap sensitive lines can effectively solve the problem of magnetic field interference. It is worth noting that it is necessary to form a closed and magnetic circuit. It is more effective to reduce the magnetic resistance of the magnetic circuit.
(2) High-frequency coupling refers to a trace longer than 1/4 wavelength. Due to the standing wave of voltage and current appearing in the circuit, the coupling amount is enhanced, which can be solved by the following method:
a. Try to shorten the grounding wire and use the surface contact with the outer casing as much as possible.
b. Rearrange the input and output lines of the filter to prevent coupling between the input and output lines to ensure that the filtering effect of the filter does not change.
c. The shielded cable shield is grounded at multiple points.
d. Connect the floating pin of the connector to ground potential to prevent its antenna effect.
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