Crosstalk interference is caused by the coupling between adjacent lines. The higher the frequency, the greater the crosstalk interference. The worse the capacitor stability, the more serious the crosstalk; In addition, low characteristic impedance is conducive to low cross talk, and the smaller the dielectric coefficient of insulation material is, the lower the cross talk will be. Only when the theory, process, processing, cost and specification requirements of customers are fully understood, can the wire rod development be done well.
When a pair of signal transmission line of high frequency capacitance inductance effect and Impedance matching effect, produces to the adjacent interference phenomena caused by signal line.
NEXT(Near End Cross Talk)--- Near End Cross Talk FEXT(Far End Cross Talk)--- Near End Cross Talk dB=20 Log(V1/V0) V1 --- Near End Cross Talk dB=20 Log(V1/V0) V1 --- Near End Cross Talk dB=20 Log(V1/V0
Xtalk, Cross talk test graphics
Its measurement can be measured by NA or TDR, and its calculation formula is as follows:
If Xtalk value is close to 0 dB(or nearly 100%), it means that the situation of noise interference is more serious; otherwise, if Xtalk dB value is larger (or nearly 0%), it means that the situation of noise interference is less
SSN (synchronous switching noise) ※ noise includes crosstalk, but crosstalk does not include noise
Switching noise is caused by the inductive coupling between differential pairs. When the current on the transmission line changes, the inductive voltage on the adjacent transmission line will be coupled and the induced current will be aroused, which will cause interference to the signal on the adjacent transmission line.
Due to the characteristics of the differential signal, the difference pair can be excited into the odd mode, under which the difference has a very good suppression effect on the noise of coupling itself. In addition, the interference of other adjacent difference pairs can be weakened by shielding the aluminum foil of the line package.
Wire crosstalk interference
In high frequency communication, we are more interested in the crosstalk interference. Crosstalk interference is due to the parasitic inductance between adjacent transmission lines at home or on, capacitance coupling noise. Had a great influence on the signal on the transmission line, must be controlled, otherwise it will cause the serious distortion of signal waveform, lead to the receiver misinterpret. Crosstalk interference is more serious with the increase of frequency. The size of the crosstalk can be measured by NA and TDR, as follows:
How crosstalk works
Crosstalk can be understood from the perspective of capacitive inductance coupling or from the perspective of differential signals and common mode components.
Description of coupling Angle:
When dynamic online have a signal through, rising in the signal delay area (namely the area of voltage and current changes). Due to the line for cooperation between mutual inductance and mutual capacitance of the lotus root, in the static line general induction current, because of the noise current felt on each direction on the static line impedance are the same, so the forward and backward will be equal to the electrical flow. Back in proximal half backward flow, produce near end crosstalk; The other half flows forward to the remote, producing remote crosstalk.