pcb filter

Tests showing the balance between frequency resolution and time. The local oscillator provides a "scan" of the frequency into the mixer, and each scan in the mixer output provides a different frequency and its corresponding value. The resolution filter is set in a user-optional frequency range, known as the resolution bandwidth (RBW). The narrower the filter bandwidth, the higher the resolution of the measuring instrument and the better the noise elimination of the instrument. The RBW filter is followed by a detector to measure the instantaneous frequency power of each frequency value. Because this method can provide a high dynamic range, its main advantage is that it can calculate the amplitude value of a frequency point at a point in time. 

If the RBW filter is designed to be too narrow, it will take longer to complete a scan of the RF input, and some changes in the input RF signal will not be detected. Scanning in a frequency domain or several passbands will take a considerable amount of time. The premise of this test technique is to assume that the signal will not change significantly during the test time during which multiple scans are carried out. Therefore, a relatively stable and unchanging input signal is a must. If the signal changes frequently, you may not get a result.

For example, it shows the results of an RBW logic analyzer test where the frequency starts at Fa and suddenly changes to Fb. When the scan reached Fb, the signal had disappeared and could not be measured. Therefore, the scan of RBW spectrum analyzer could not provide trigger at Fb, so it could not store a comprehensive signal situation within a period of time. This is a classic example of the balance between frequency resolution and test time, and is the Achilles' heel of the RBW spectrum analyzer.

However, the latest scanning spectrum analyzer is much faster than the traditional analog processing based equipment, a modern excellent scanning spectrum analyzer architecture. Traditional analog RBW filters have been digitally enhanced to facilitate fast and accurate narrow-band filtering. However, filters, mixers, and amplifiers prior to an ADC are analog, and in particular, need to take into account nonlinearity and noise in an ADC. Therefore, there is a place for analog spectrum analyzer, which can avoid the above problems.

In the actual production process, there are many reasons for the surface bubbling, the author can only do a brief analysis, for different manufacturers of equipment technical level may appear different reasons caused by the bubbling phenomenon, the specific situation to be specific analysis, not generalize, copy rigid; The analysis of the above reasons is not primary, secondary and important, basically according to the production process to do a brief analysis, in this series, just to provide you with a direction to solve the problem and a broader vision, I hope to everyone's process production and problem solving, can play a role in attracting jade!

1. In the process of graphic transfer, insufficient washing after development, too long placement time after development or too much dust in the workshop will cause poor cleanliness of the board, and the fiber treatment effect is slightly poor, which may cause potential quality problems;

2. There is organic pollution in the plating tank, especially oil pollution, which is more likely to occur in the automatic line.

3. Copper plating pre-leaching tank should pay attention to timely replacement, too much pollution in the tank, or too high copper content, will not only cause the cleanliness of the board, but also cause rough surface defects;

4. In addition, in winter, when the tank liquid in some factories is not heated, special attention should be paid to the live into the tank of the production process, especially the plating tank with air stirring, such as copper nickel; For nickel cylinder in winter, it is best to add a warm water bath before nickel plating,(the water temperature is about 30-40 degrees), to ensure that the initial dense nickel layer deposition is good;