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Hardware related development
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Preface
HDMI, LVDS, and MIPI-DSI are output on the front. There is also a commonly used display interface here, which is VGA. This is not used much anymore, and most boards are HDMI.
This article analyzes the baseboard VGA circuit.
VGA interface
VGA (Video Graphics Array) is a computer display standard using analog signals proposed by IBM in 1987. The VGA interface is a dedicated interface for computers to output data using the VGA standard. The VGA interface has a total of 15 pins, divided into 3 rows, with 5 holes in each row. It is the most widely used interface type on graphics cards, and most graphics cards have this interface. It transmits red, green and blue analog signals as well as synchronization signals (horizontal and vertical signals).
VGA circuit analysis
Development board backplane schematic diagram
VGA interface
The bottom board here is a bit complicated. Let’s start the analysis from the pinout or VGA interface, starting from the pins coming out of the VGA black core board:
It seems that the VGA here is from The EDP signal is converted. When we look at EDP, we also output the EDP interface signal:
Confirm that it is converted:
The RTD2166 chip is used:
This is a DP to VGA solution chip (IT6516/RTD2166/CS5212), so the VGA on the baseboard is a DP conversion solution.
TP_0.7 is not actually connected. It may be a hole made to facilitate the measurement of whether the circuit voltage is intact (confirm with the solution provider, if the measurement here is 3.3V, it means normal).
The conversion solution is used, which is equivalent to a module made of a DP to VGA solution, so this module can be made separately as a board for testing.
Connector packaging
QFN package
QFN (Quad Flat No-leads Package), one of the surface mount packages. QFN is the name specified by the Japan Electronics Machinery Industry Association. There are electrode contacts on the four sides of the package. Since there are no leads, the mounting area is smaller than QFP and the height is lower than QFP. However, when stress occurs between the printed circuit board and the package, it cannot be relieved at the electrode contact. Therefore, it is difficult to have as many electrode contacts as QFP pins, which are generally from 14 to 100. There are two types of materials: ceramic and plastic. When there is an LCC mark, it is basically ceramic QFN. The center distance between electrode contacts is 1.27mm. Plastic QFN is a low-cost package based on glass epoxy resin printed substrate. In addition to 1.27mm, the electrode contact center distance also has two types: 0.65mm and 0.5mm. This kind of packaging is also called plastic LCC, PCLC, P-LCC, etc.
Summarize
Since it is not directly output by the chip, we currently do not consider implementing VGA on our own baseboard. We can directly use the HDMI to VGA module.
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Next article: "Hardware Development Notes (16): RK3568 baseboard circuit mipi camera interface schematic analysis, mipi camera detailed explanation 》
The blog address of this article:https://hpzwl.blog.csdn.net/article/details/134849296