“The combination of good power supply decoupling technology with rigorous PCB layout and Vcc leads (star topology) can lay a solid foundation for any RF system design. Although there are other factors in the actual design that reduce the system performance index, having a “noise-free” power supply is the basic element for optimizing system performance.
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(1) The power cord is an important way for EMI to enter and exit the circuit. Through the power cord, external interference can pass into the internal circuit and affect the RF circuit index. In order to reduce electromagnetic radiation and coupling, the loop area of one side, secondary side, and load side of the DC-DC module is required to be small. No matter how complicated the form of the power circuit, its large current loop should be as small as possible. The power cord and ground wire should always be placed close together.
(2) If a switching power supply is used in the circuit, the layout of the peripheral components of the switching power supply should comply with the principle that the return path of each power is very short. The filter capacitor should be close to the relevant pins of the switching power supply. The common mode Inductor should be close to the switching power supply module.
(3) The long-distance power line on the board cannot approach or pass through the output and input terminals of the cascaded amplifier (gain greater than 45dB) at the same time to prevent the power line from becoming an RF signal transmission path, which may cause self-excitation or reduce the sector isolation . High-frequency filter Capacitors need to be added to both ends of long-distance power lines, and even high-frequency filter capacitors must be added in the middle.
(4) Three filter capacitors are combined in parallel at the power inlet of the RF PCB, and the respective advantages of these three capacitors are used to filter out the low, medium and high frequency signals on the power line, for example: 10uf, 0.1uf, 100pf. And approach the input pins of the power supply in order from largest to smallest.
(5) To feed the small-signal cascaded amplifier with the same set of power supplies, start from the final stage and supply power to the previous stage in turn, so that the EMI generated by the final circuit has less impact on the previous stage. And there are at least two capacitors for each yi level of power filtering: 0.1uf, 100pf. When the signal frequency is higher than 1GHz, a 10pf filter capacitor should be added.
(6) For low-power Electronic filters commonly used, the filter capacitor should be close to the Transistor pin, and the high-frequency filter capacitor should be closer to the pin. The triode chooses the lower cut-off frequency. If the triode in the electronic filter is a high-frequency tube, it works in the amplifying area, and the layout of the peripheral components is unreasonable, and it is easy to produce high-frequency oscillation at the output end of the power supply.
The linear voltage regulator module may also have the same problem. The reason is that there is a feedback loop in the chip and the internal triode is working in the amplifying area. In the layout, the high-frequency filter capacitor is required to be close to the pin to reduce the distributed inductance and destroy the oscillation condition.
(7) The size of the copper foil of the POWER part of the PCB should meet the requirements of the large current flowing through it, and the margin should be considered (generally referred to as 1A/mm line width).
(8) The input and output of the power cord cannot be crossed.
(9) Pay attention to power supply decoupling and filtering to prevent interference from different units through the power line. The power lines should be isolated from each other during power wiring. The power line is isolated from other strong interference lines (such as CLK) with a ground line.
(10) The power wiring of the small-signal amplifier needs ground copper and grounding via isolation to prevent other EMI interference from entering and deteriorating the signal quality of this level.
(11) Different power layers should avoid overlapping in space. The main purpose is to reduce the interference between different power supplies, especially between power supplies with very different voltages. The problem of overlapping power planes must be avoided. If it is unavoidable, consider the intermediate ground layer.
(12) The PCB layer distribution is convenient to simplify the subsequent wiring processing. For a four-layer PCB (a commonly used circuit board in WLAN), in most applications, the top layer of the circuit board is used to place components and RF leads, and the second layer is used as System ground, the power part is placed on the third layer, and any signal lines can be distributed on the fourth layer.
The continuous ground plane layout of the second layer is necessary to establish an RF signal path with controlled impedance. It is also convenient to obtain the shortest possible ground loop, providing a high degree of electrical isolation for the yi layer and the third layer, making the two layers The coupling between is very small. Of course, other board layer definition methods can also be used (especially when the circuit board has a different number of layers), but the above structure is a proven successful example.
(13) The large-area power layer can make Vcc wiring easy, but this structure is often the fuse that causes the deterioration of the system performance. Connecting all the power leads together on a larger plane will not avoid the pins. Noise transmission between. Conversely, if a star topology is used, the coupling between different power supply pins will be reduced.
The combination of good power supply decoupling technology with rigorous PCB layout and Vcc leads (star topology) can lay a solid foundation for any RF system design. Although there are other factors in the actual design that reduce the system performance index, having a “noise-free” power supply is the basic element for optimizing system performance.
(1) The power cord is an important way for EMI to enter and exit the circuit. Through the power cord, external interference can pass into the internal circuit and affect the RF circuit index. In order to reduce electromagnetic radiation and coupling, the loop area of one side, secondary side, and load side of the DC-DC module is required to be small. No matter how complicated the form of the power circuit, its large current loop should be as small as possible. The power cord and ground wire should always be placed close together.
(2) If a switching power supply is used in the circuit, the layout of the peripheral components of the switching power supply should comply with the principle that the return path of each power is very short. The filter capacitor should be close to the relevant pins of the switching power supply. The common mode inductor should be close to the switching power supply module.
(3) The long-distance power line on the board cannot approach or pass through the output and input terminals of the cascaded amplifier (gain greater than 45dB) at the same time to prevent the power line from becoming an RF signal transmission path, which may cause self-excitation or reduce the sector isolation . High-frequency filter capacitors need to be added to both ends of long-distance power lines, and even high-frequency filter capacitors must be added in the middle.
(4) Three filter capacitors are combined in parallel at the power inlet of the RF PCB, and the respective advantages of these three capacitors are used to filter out the low, medium and high frequency signals on the power line, for example: 10uf, 0.1uf, 100pf. And approach the input pins of the power supply in order from largest to smallest.
(5) To feed the small signal cascaded amplifier with the same set of power supplies, start from the final stage and supply power to the previous stage in turn, so that the EMI generated by the final circuit has less impact on the previous stage. And there are at least two capacitors for each yi level of power filtering: 0.1uf, 100pf. When the signal frequency is higher than 1GHz, a 10pf filter capacitor should be added.
(6) For low-power electronic filters commonly used, the filter capacitor should be close to the Transistor pin, and the high-frequency filter capacitor should be closer to the pin. The triode chooses the lower cut-off frequency. If the triode in the electronic filter is a high-frequency tube, it works in the amplifying area, and the layout of the peripheral components is unreasonable, and it is easy to produce high-frequency oscillation at the output end of the power supply.
The linear voltage regulator module may also have the same problem. The reason is that there is a feedback loop in the chip and the internal triode is working in the amplifying area. In the layout, the high-frequency filter capacitor is required to be close to the pin to reduce the distributed inductance and destroy the oscillation condition.
(7) The size of the copper foil of the POWER part of the PCB should meet the requirements of the large current flowing through it, and the margin should be considered (generally referred to as 1A/mm line width).
(8) The input and output of the power cord cannot be crossed.
(9) Pay attention to power supply decoupling and filtering to prevent interference from different units through the power line. The power lines should be isolated from each other during power wiring. The power line is isolated from other strong interference lines (such as CLK) with a ground line.
(10) The power wiring of the small-signal amplifier needs ground copper and grounding via isolation to prevent other EMI interference from entering and deteriorating the signal quality of this level.
(11) Different power layers should avoid overlapping in space. The main purpose is to reduce the interference between different power supplies, especially between power supplies with very different voltages. The problem of overlapping power planes must be avoided. If it is unavoidable, consider the intermediate ground layer.
(12) The PCB layer distribution is convenient to simplify the subsequent wiring processing. For a four-layer PCB (a commonly used circuit board in WLAN), in most applications, the top layer of the circuit board is used to place components and RF leads, and the second layer is used as System ground, the power part is placed on the third layer, and any signal lines can be distributed on the fourth layer.
The continuous ground plane layout of the second layer is necessary to establish an RF signal path with controlled impedance. It is also convenient to obtain the shortest possible ground loop, providing a high degree of electrical isolation for the yi layer and the third layer, making the two layers The coupling between is very small. Of course, other board layer definition methods can also be used (especially when the circuit board has a different number of layers), but the above structure is a proven successful example.
(13) The large-area power layer can make Vcc wiring easy, but this structure is often the fuse that causes the deterioration of the system performance. Connecting all the power leads together on a larger plane will not avoid the pins. Noise transmission between. Conversely, if a star topology is used, the coupling between different power supply pins will be reduced.
The combination of good power supply decoupling technology with rigorous PCB layout and Vcc leads (star topology) can lay a solid foundation for any RF system design. Although there are other factors in the actual design that reduce the system performance index, having a “noise-free” power supply is the basic element for optimizing system performance.
The Links: NL10276BC28-27E EPC2LI20N