Slow rising edge signal of EMC immunity

In EMC design and processing, engineers pay attention to rapidly changing signals, because the rising edge time of these signals is very short. From the perspective of spectrum analysis, there will be more high-frequency harmonics in the signal, leading to EMC design Becomes difficult. Moreover, the fast rising edge signal makes the problems of reflection, crosstalk, electromagnetic radiation, and ground bounce more serious, and the noise problem is more difficult to solve.

Slow rising edge signal of EMC immunity

Author: Li Yijun, Source: Taolue Technology EMC

In EMC design and processing, engineers pay attention to fast-changing signals, because the rising edge time of these signals is very short. From the perspective of spectrum analysis, there will be more high-frequency harmonics in the signal, leading to EMC design Becomes difficult. Moreover, fast rising edge signals make problems such as reflection, crosstalk, electromagnetic radiation, and ground bounce more serious, and noise problems are more difficult to solve.

The following figure shows the time-domain waveform and spectrum envelope of the trapezoidal pulse waveform; A=amplitude, tr=rising edge time, τ=average width. It can be seen from the figure that the rise time has an impact on the existence of high-frequency harmonics. It can be seen that there are good reasons to focus on fast rising edge signals in EMC design, and in almost all interference emission tests, fast rising edge signals are the most important factor. Do you only need to deal with this type of signal? Since there are also anti-interference items in the EMC test, the processing of slow signals also needs to be dealt with.

Slow rising edge signal of EMC immunity

Because the digital signal rises or falls slowly. As shown in the figure below, since the rise time of t1-t2 becomes slower, the noise margin is reduced, and the possibility of malfunction is greatly increased. The signal is in the middle of the change, especially when the noise margin near the threshold (near VILmax-VIHmin) is the lowest, so even if the noise superimposed on the signal is small, it will cause malfunction.

Slow rising edge signal of EMC immunity

In practice, when the rising edge is slower or slower, the more straightforward solution is to reduce the pull-up resistance, load capacitance, and parasitic capacitance. In this way, the charging time constant of the signal line can be reduced, and the rise can be accelerated to reduce the t1-t2 interval. Reduce the possibility of malfunction.

Finally, there are many kinds of immunity problems encountered in practice, and it is a relatively straightforward method to deal with the interfered object. In practice, the methods are diverse, such as reducing interference, optimizing interference paths, and so on.

Slow rising edge signal of EMC immunity

Author: Li Yijun, Source: Taolue Technology EMC

In EMC design and processing, engineers pay attention to rapidly changing signals, because the rising edge time of these signals is very short. From the perspective of spectrum analysis, there will be more high-frequency harmonics in the signal, leading to EMC design Becomes difficult. Moreover, the fast rising edge signal makes the problems of reflection, crosstalk, electromagnetic radiation, and ground bounce more serious, and the noise problem is more difficult to solve.

The following figure shows the time-domain waveform and spectrum envelope of the trapezoidal pulse waveform; A=amplitude, tr=rising edge time, τ=average width. It can be seen from the figure that the rise time has an impact on the existence of high-frequency harmonics. It can be seen that there are good reasons to focus on fast rising edge signals in EMC design, and in almost all interference emission tests, fast rising edge signals are the most important factor. Do you only need to deal with this type of signal? Since there are also anti-interference items in the EMC test, the processing of slow signals also needs to be dealt with.

Slow rising edge signal of EMC immunity

Because the digital signal rises or falls slowly. As shown in the figure below, since the rise time of t1-t2 becomes slower, the noise margin is reduced, and the possibility of malfunction is greatly increased. The signal is in the middle of the change, especially when the noise margin near the threshold (near VILmax-VIHmin) is the lowest, so even if the noise superimposed on the signal is small, it will cause malfunction.

Slow rising edge signal of EMC immunity

In practice, when the rising edge is slower or slower, the more straightforward solution is to reduce the pull-up resistance, load capacitance, and parasitic capacitance. In this way, the charging time constant of the signal line can be reduced, and the rise can be accelerated to reduce the t1-t2 interval. Reduce the possibility of malfunction.

Finally, there are many kinds of immunity problems encountered in practice, and it is a relatively straightforward method to deal with the interfered object. In practice, the methods are diverse, such as reducing interference, optimizing interference paths, and so on.

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