Weak current College】 【AV systems integration engineering common signal Fuzzy Tail phenomenon analysis --- Power By】 【China power house network.

The current system integration project, particularly the VGA signal long-distance transmission is a project of the more common issues, the so-called transmission system means the export from a computer to the display section of the portal all the links in between, including Distributor, matrix, cables and graphics controller, and so on, because the signal transmission distance, the transmission system parameters and surrounding electromagnetic environment on signal quality impact cannot be ignored, common phenomena manifested as: image blur, Darken, smearing and ghosting, and image display instability (e.g. bounce or black screen, etc), etc.

The above phenomenon causes different, solution. We will which is divided into four categories:

Due to the transmission system of amplitude-frequency characteristics and the Group delay characteristics of image blur, Darken, tail;
Since the equipment generates self-excited or environmental electromagnetic interference generated by high-frequency interference;
Due to improper handling of the system power supply ground caused by the low-frequency interference;
Because device or transmission system or add plug-ins such as impedance mismatch cause ghosting reflection and displays unstable.
This article first Fuzzy Tail phenomena make analysis and provide solutions, several other situations will be addressed in the future.

Cause fuzzy tail and darken the phenomenon from the principle can be divided into two parts, one is the signal during the transfer process of amplitude-frequency characteristics of both bandwidth and not enough of fuzzy and darkens; second, the transfer process group delay characteristics in the tail phenomenon. Amplitude-frequency characteristics; in short it is a different frequency components and the relationships between amplitude attenuation to 1024 x 768 monitor resolution, for example, generally believed that the bandwidth between the 90) 120MHz, therefore we care about 100 m 100 attenuation. The matrix switch and splitter, itself with a certain amount of improvement and drive capability, meet signal transmission is not a problem, but taking into account the loss of connectors, this part of the lift and drive capability in transmission systems design and analysis. Currently cause fuzzy, Darken, smearing problem is concentrated mainly in the transport of cables, because transmission using cable, amplitude-frequency characteristic, the attenuation is opposed to the number type. (Shown in Figure 1-1 in A curve)



That is, the higher the frequency, the greater the specific indicators for the attenuation of the auspicious sees the table

-SYV-75-2SYV-75-3SYV-75-5-1LG-RG59/51MHZ/100 m-3dB-2.2dB-1.2dB-1dB100MHZ/100 m-22dB-15dB-10dB-8Db200MHZ/100 m-38dB-24dB-15dB-12dB diameter-15mm22mm18mm due to attenuation of frequency variable, so the resulting image (brightness enough) and fuzzy, to improve this situation, you should make the transmission equipment of characteristic curve is logarithmic type, as in Figure 1-1 of the B curve. But in the circuit practice not possible to reach this ideal State, generally is parabolic as in Figure 1-1 C curve. The result is shown in Figure 1-1 D curves. We generally concerned about bandwidth shaping after synthesis, guarantees that the line transmission bandwidth of 80), can obviously 120MHz improve darken, blur, etc to ensure its high frequency components of the transmission and display. There are also some other brands of drive, due to the design and a variety of reasons, the bandwidth is narrow, in about 30-50 MHz), which has promoted improved, but does not address the underlying problem.

Group delay characteristics (Group Delay) refers to: signal transfer process, because the distribution parameters for existence, the transmission system characteristics parameter is not a pure resistance, but by the resistance, capacitance, inductance network, therefore different frequency components in the same media transfer, arrival time or have the phase difference, specific mathematical models and analysis here, no detail on its actual results. This species will result in delay of signal waveform of the rear, which resulted in the tail. Figure 2-1. In the transport equipment, to resolve the issue, group delay on transport systems, pre-emphasis, such as the predistortion figure 2-2, after the waveform synthesis will be significantly improved, as in Figure 2-3. Different cable and different transmission distance of its amplitude-frequency characteristics and different, group delay characteristics should be adjusted according to different circumstances. According to our research, transfer system, the better the amplitude-frequency characteristics, group delay characteristics is its better. That is, generally speaking, the thicker the line attenuation and smearing it smaller.



In the absence of compensation, the 65HZ 1024 x 768 monitor resolution RGBHV signal (100MHZ) theoretically use SYV-75-3 cable transmission only 20 meters, SYV-75-5-1 cable can only transfer 30 m. But in engineering practice most contractors and users think-6dB band loss transfer image acceptable-9dB band loss transfer of images to be able to tolerate, but group delay characteristics you must adjust the delay pre-emphasis to address the problem less smearing.

For compensation of amplitude-frequency characteristics and cable group delay characteristics of long-line driven compensation allocator (Line Driver) to solve engineering on signal long-distance transmission, General view, 2 or 3 + 3 + 4 cable distance should be controlled at about 20 m, 75-5 cable should be about control and then 50m is greater than this distance, such as, using long line driver for compensation. For work involving the use of cable specification, its DC impedance, equivalent impedance, distribution parameters such as capacitors, inductors, therefore, must be on a different situation to compensate, in theory, capacitors, inductors and resistance adjustments can be resolved, but the practical application, capacitance, inductance of adjustable range is small and the R, G, B triple signal at the same time adjustment and to adjust the volume to be consistent, thus achieving continuous adjustable difficult at present to use pre-designed network superposition, i.e. for grading-adjust rather continuous adjustment, but must be adjustable, fixed some compensation circuit, it is not possible to comply with the scene of different situations should not be referred to as long-line drive.

Long line driven compensation equipment according to different specifications and cable attenuation characteristics and different length of the cable, the cable against several simulation curve characteristics, a tranche of gain group delay compensation and, most device compensation up to 8/16 (per level of about 15 m), the device width up to 200MHz (without compensation), adjusted transport system bandwidth of up to 80) 120MHz. VGAD-1x2CC/L 8 shift adjustment compensator for 10dB/100 m, 100MHz cable, parameters, adjusting the when starting, 20m 100m is the maximum, while VGAD-1x2CC/LT 16 rail adjustment device, when you start adjustment, 50m 300m at maximum, from the current look to meet actual requirements engineering use.



For image instability and even frequency phenomena such as black, long-line compensation drive can also sync signal digitally correction (ADSP, this technique non-this article discusses the key, do not detailed here). Long cable compensation drive operation is convenient, the device front panel design a touch screen to compensate stalls, in addition, the device also adds RS-232 interface control (VGAD-1x2CC/LT), ease of customer use of control or PC on its control and saves device, as in Figure 3-1, example on matrix switch, the length of the input line and the output line length is equal, for compensation, in principle, in the enter a portion of the different compensation so that input signal when the matrix entry, because the output cable length and inconsistencies, but also for its different compensation equipment more, if the figure 3-2 of the programme, while the complete switch, input, output, line length information notification long line drive, the length of the different compensation adjustments, saving device, reducing investment.

The above is only applied to engineering and related causes of Jade's view, such as inadequate please correct me!