"XX project FM has problems! Hurry to arrange help analysis!"
"XX customer feedback Our products GPS unable to position! Speed support, production line is waiting!"
"We are all produced, because you have to change this!"
We often encounter such customers to complain, customers and our supporters have to go to "fire fire", and their customers will be complained, indicators, and our technology by their customers. Personnel are also very anxious.
In order to make our GPS LNA and FM LNA a better role, reduce the impact of products on the project process, we organize the following contents, as a supplementary document other than the reference design, assist customers in designing, try to avoid the problem, in the case Reduce the "fire status" and achieve the effect of halving. The following information is that after the individual is organized, some of the correct use pose is summarized, and experts are welcome to shoot bricks.
The following postures are based on a common fact: GPS (-130dBM level) and FM (-90dBM level) signal are extremely small, very fragile, need you and everyone's focus, in order to show their wonderful.
First, LNA principle
LNA is a simple child, only five signal VCC, EN, IN, OUT, GND. In / OUT matches what the design information given by the original factory.
in principle:
Reserve a small amount of redundant circuits, increasing commissioning methods and improving means.
Recommended posture:
1, in addition to the conventional filter capacitor, add a series position, default can be applied to the 0OHM resistance, which is easy to determine whether there is interference through VCC. If it is, it can be replaced with 10OHM level resistance or magnetic beads; for one The power supply is particularly useful for many ICs.
2, the EN feet also leave a pair of RC filter circuits, and if the land is nervous, leaving only one NC capacitive bit of the land, the reason is the same.
Second, LNA layout
in principle:
Keep away from interference sources;
Recommended posture:
1, must be as close as possible to the antenna feed, prioritize the position of the main board, less disturbed here;
2. Keep away from such as Memory, RF PA, Audio Pa, Backlight Circuit, Flash Circuit, and the like, and do not (this is more concealment, must focus on). If you can build a tin house (shield) is more ideal.
3, away from the assembly components that are easy to generate or propagate the source, such as LCD, FPC cable, battery, speaker, etc.
4, the details of the details are optimized, through the layout to reach the radio trace as short as possible, less bend;
5, the radio frequency line is taken prioritize on the motherboard to avoid crossing through the FPC soft board. If the design needs to be across, it is recommended to use the coaxial mode.
Third, LNA Wiring
in principle:
1, do a good job, avoid introducing interference;
2, in, OUT line as short as possible, less restrictive layer;
Recommended posture:
1. Try to do the impedance control as much as possible, the IN / OUT cable is basically basic, and most of the schuri lion can handle it. It is necessary to supplement that the width and interlayer connections of the package can be borne, and the signal outside the protection line can be paid, try not to stream the power or signal line.
2, VCC and EN are more commonly handled, so there is a suggestion of the principle, increase the recommendations of the principle part, but also take the initiative to do the line protection of these two networks, after all, the disease is good.
3. It is easy to be ignored by everyone is GND processing.
A, LNA, filter capacitor, GND, matching material, please connect (thick, short GND line), then at the GND of the IC (the best) to the primary;
B, do not do A request, please direct the GND PIN directly to the main ground; the corresponding lower well avoids the GND other than the main land, and the common practice is the corresponding lower well except for the land outside the land. Clearance.
Fourth, the whole machine environment
in principle:
Reduce or switch interference generation, propagation paths.
Recommended postures (including but not limited):
1, LCD must take a metal frame, the metal frame should be well grounded (at least 3 points of the main board);
2, metal parts without specific signal functions inside the machine are well grounded, especially in the metal of the casing or metal front case;
Original link: https://www.eeboard.com/news/gpsfm-lna/
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