With the increase of electronic equipment, the phenomenon of electromagnetic interference (EMI) becomes more and more serious.In the conducted interference, the power line conducted interference is the most serious.The main way to suppress interference on power lines is to use EMI filters, which are usually characterized by insertion loss.However, in actual use, even if the insertion loss design of EMI filter meets the standard, it may not get the best filtering effect due to the change of source impedance and load impedance.[1]
Insertion loss refers toThe loss of load power caused by the insertion of an element or device somewhere in the transmission system is expressed as the ratio in decibels between the power received on the load before the element or device is inserted and the power received on the same load after the insertion.
Insertion loss refers totransmitterThe signal loss caused by inserting cables or components between the receiver and the receiver, usually referred to as attenuation.Insertion loss is expressed in decibels (dB) corresponding to the received signal level.
Circuit for measuring insertion loss
2. Insertion loss mostly refers to the loss of power. Attenuation refers to the decrease of signal voltage amplitude relative to the original signal amplitude.For example, for an ideal lossless transformer, the original and auxiliary ideal transformers are lossless, that is, the insertion loss is zero.The concept of insertion loss is generally used inwave filterIn, indicates the loss of signal power before the filter is used and not used.
The insertion loss of the channel refers to the ratio of the output optical power of the output port to the input optical power of the input port, in dB.Insertion loss is related to input wavelength and switch state.Defined as: IL=- 10log (Po/Pi)
Where:
Pi - → optical power input to the input port, in mw;
Po - → optical power received from the output port, in mw.
For OLP, it can be divided into insertion loss at the transmitter and insertion loss at the receiver.
Minimum insertion loss
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The minimum insertion loss refers to the minimum insertion loss value obtained at all frequency points when the source impedance and load impedance of a filter whose structure and circuit parameters have been determined independently change within a certain range. It means that once the parameters and structure of the filter are determined, the insertion loss of the filter is only related to its source and load impedance. Therefore, in practical use,The filter can be selected according to the worst case, that is, the filter can be selected according to the minimum insertion loss of the filter[2]
How to measure insertion loss?
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If the terminal impedance meets the standard, it becomes meaningful to measure the insertion loss.However, the results obtained in this way can only be used for identical circuits.The most common setting is to make the power supply and negative load impedance 50 Ω.
The most important point of insertion loss measurement is consistency.EFT adopts the following methods:
It is easy to measure insertion loss with spectrum analyzer, FM receiver or tracking generator.Without a filter, a zero dB reference point is established.Then insert a filter and record the attenuation provided within the required frequency range.For the power line filter, we are interested in two different modes of attenuation:
common mode(CM) - Line (live line and neutral line) on both sides of the signal to ground.
Differential mode(DM) - Line to line where the signal exists on one side.
Accordingly, we can study CM insertion loss or DM insertion loss, or both.
For common mode, the live wire and neutral terminal are at the same potential (the same magnitude and phase), which can be considered as parallel. CM current flows between this group of wires and the common wire (ground).Connect the live wire and neutral wire on both sides of the filter together (Figure 1) to measure CM insertion loss.
