The most effective method to deal with the interference problem of pulse group generator
Many people in the process of using the pulse group generator should have encountered the problem of interference of the pulse group generator, then how to solve it? The usual methods are as follows
The first is absorption and filtering
The original intention of pulse group generator test is to carry out common mode interference test. However, the waveform front of the interference pulse is very steep and the duration is very short, so it contains extremely rich high-frequency components. As a result, during the transmission of interference waveform, some interference will escape from the transmission cable to form radiation, so that the device will eventually be affected by the combined interference of conduction and radiation.
For PGS interference, one of the most common suppression methods is to use filtering (using power and signal line filters for filtering) and absorption (using ferrite core to absorb).The ferrite core absorption scheme is very cheap and effective.
The second method is the transient interference suppression device
Since the signal of pulse group generator is with high frequency and high voltage pulse, transient voltage absorption device can be used to absorb the pulse group signal to suppress the pulse group signal.
There are many kinds of transient voltage absorption devices, but they mainly include gas discharge tubes, metal oxide piezoresisors, silicon transient voltage absorption diodes and solid discharge tubes.
Considering the characteristics of high frequency and high speed of pulse group signals, only metal oxide piezoresisors and silicon transient voltage receiving diodes are suitable for transient voltage absorption devices.
Both devices can be used in principle for interference suppression of power lines, but voltage-sensitive resistors may be more common in comparison because they are cheaper and more responsive.
In addition, the inherent parasitic capacitance of piezoresisors has no negative effect on the power line of 50Hz. For signal lines, both devices can be used, but silicon transient voltage absorption diodes may be more suitable, because in the PCB level of protection, silicon transient voltage absorption diodes have a wide range of voltage levels, there is a lot of choice;
At the same time, the limiting voltage is more accurate (the residual voltage of diode action is low, close to the breakdown voltage), especially suitable for the protection of semiconductor integrated circuit and other electronic components.
In addition, the parasitic capacitance of silicon transient voltage absorption diodes is smaller than that of piezoresisors, and it is less harmful to transmit signals on the line. For high speed transmission signal and specially processed, parasitic capacitance small silicon transient voltage absorbing diode can choose (and high-speed diodes and transient voltage silicon absorption diode series, due to a level pF the diode junction capacitance, after dealing with the series of silicon transient voltage absorption level pF the equivalent capacitance diode), particularly suitable for the protection of these lines.
And then shielding
Considering that the front edge of the PGS signal is very steep and the pulse width is very narrow, the harmonic components are extremely rich, and the frequency with a large amplitude should reach at least 60MHz. For the power line and signal line in the test, the length is only 1m. Since the length can be compared with the wavelength of transmission frequency, it cannot be treated as ordinary power line and signal line. When the signal is transmitted above, part of it enters the sample through the line (conduction). Part of the escape from the circuit becomes a radiation signal into the sample (radiation).Therefore, the interference suffered by the sample is actually the combination of conduction and radiation, that is, when doing the pulse group test, there is actually a radiation field around the conductor being tested. For radiation interference, a common method of suppression is shielding, including shielding of the equipment shell, local shielding within the equipment, and shielding of transmission lines (shielding lines, coaxial cables and twisted pair wires, etc.).
Finally, structure and grounding
The structure and grounding are also important aspects to suppress pulse group interference.
As a non-metal shell electronic equipment, first of all, the power line away from the ground, the grounding path is long, the grounding effect is greatly reduced.
Secondly, signal line 1 is far away from the ground, which leads to the interference pulse applied on the power line and signal line 1. When the common mode interference current of the pulse group is applied on the power line and signal line 1, it shall pass through the interconnect line and the circuit board below, and finally enter the ground through the grounding terminal. Because of the high impedance of the interconnect and the long grounding path (the grounding impedance is also large), the risk of electromagnetic compatibility is greatly increased.