A good printed circuit board (PCB) design is required for achieving good RF performance, with two layers to design. Since the NRF401 peripheral components are small, it is currently the highest integration RF transceiver chip and integrates baseband processing. It is convenient for design, but actually due to the characteristics of high frequency circuits, high operating frequency (UHF), and NRF401 PCB design is a mixed signal circuit. Design, although NRF401 has greatly simplified RF circuit design and requirements, it still needs very much attention when designing. Generally, the following principles need to follow:
1
When the wiring does not only consider whether the line can be made, if the PCB wiring layout is unreasonable, it may greatly affect the performance and communication distance, which is the characteristics of the RF circuit design. Therefore, the PCB is divided into two partial arrangements of RF circuits and control circuits.
PCB uses a double panel to be divided into element surfaces and bottom. There is a continuous ground plane at the bottom surface, the ground floor of the element surface ensures that the element is fully grounded, a large number of through-ground planes, and the ground plane of the bottom surface.
2
Suitable parts layout. The element surface of the RF circuit is centered on NRF401, and the components are closely around it, and the impact of distribution parameters should be reduced. It is important to say that the layout of VCO inductance is very important, and an optimized VCO inductor layout will provide a suitable voltage to the PLL loop filter. The components of the matching network are preferably near the NRF401 ANT1 and ANT2 to reduce stray inductance and stray capacitance.
3
The PCB partition is a separate analog part and a digital part. In all layers of the circuit board, the digital signal can only wiring the digital partial wiring of the circuit board, and the analog signal can only wiring on the analog partial wiring of the board, and analog power supply and digital power supply to be split. The DC power supply of NRF401 must be removed from the VDD foot as close as possible to high performance RF capacitor. If a small capacitor is again, it will be better (2.2uf). The power supply of the radio frequency portion and the digital circuit portion is separated, and the VSS end of the NRF401 is directly connected to the ground plane.
4
The power supply of the RF circuit uses high-performance RF capacitors to decouple, and the decoupling capacitor is as close as possible to the VDD end of the NRF401, which is generally in parallel a small value of a small value side by a larger capacity. The power supply of the NRF401 must pass well, and is separated from the digital circuit.
5
When wiring, power cords and ground lines should be rough as possible. In addition to decreased pressure drop, more important is to reduce coupling noise. Crystal traces introduced from the microcontroller cannot be too close to the data line or the control line. Pay attention to the filtering of the power supply and the trace of the power cord. The digital signal or control signal cannot be introduced into the PLL loop filter element. Try to reduce the area of the loop ring when wiring to reduce induction noise.
6
Use the correct wiring rules. The long power line should be avoided on the PCB board, all components, VDD cable, VDD desert capacitors must be as close as possible from NRF401, if the top of the PCB design is copper, VSS is required to connect to the copper surface, If the bottom layer of the PCB is paved, it will achieve better performance with a vs. pad with a vs. pad. All switch digital signals and control signals cannot pass through the PLL loop filter element and VCO inductance.
Seduce
The impact of the power supply on the NRF401 is fully considered. The power is well done, and the anti-interference of the entire circuit has solved a large half. The RF circuit is very sensitive to the power supply noise, and the RF power supply is added to reduce the interference of the power supply noise to the RF circuit. For example, the magnetic beads and capacitors can be utilized to form a п-type filter circuit, and of course the conditions are required to replace the beads when the conditions are required.
Original link: https://www.eeboard.com/news/pcb-11/
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