104 PCB layout circuit skills Q & A, help you draw the board without worry!

In electronic product design, PCB layout and wiring is an important step, and the good or bad PCB layout and wiring will directly affect the performance of the circuit.
Nowadays, although there are many software to realize PCB automatic layout and routing. But as the signal frequency continues to rise, many times, engineers need to understand the basic principles and techniques related to PCB layout and routing to make their designs flawless.

The following covers the basic principles and design techniques related to PCB layout and wiring, in the form of questions and answers to difficult questions about PCB layout and wiring.PCB layout and wiring related to the basic principles and design techniques

1, [Q] What are the issues to pay attention to when wiring high-frequency signals? [A ]

• Impedance matching of signal lines;
• Spatial isolation from other signal lines;
• For digital high frequency signals, differential lines will work better.

2、[Q] When laying out the board, if the line is dense, the over-hole may have to be more, of course, it will affect the electrical performance of the board, how to improve the electrical performance of the board? [A] For low-frequency signals, it does not matter if there are too many holes, high-frequency signals try to reduce the number of holes. If more lines can consider multi-layer board.
3、[Q] Is it better to add more decoupling capacitors on the board? [A] Decoupling capacitors need to be added at the right location with the right value. For example, in the power supply port of your analog devices, and need to use different capacitance values to filter out spurious signals of different frequencies.
4、[Q] What is the standard of a good board? [A] A reasonable layout, power line power redundancy enough, high frequency impedance impedance, low frequency alignment simple.

5、[Q] How big is the impact of through-hole and blind hole on the difference of signal? What is the principle of application? [A] The use of blind or buried holes is an effective way to improve the density of multilayer boards, reduce the number of layers and board size, and greatly reduce the number of plated through-hole. However, in comparison, through-hole is good to achieve in process and lower cost, so generally through-hole is used in design.
6、[Q] In the case of analog-digital hybrid systems, some people suggest that the electrical layer split, the ground plane to take the entire copper, others suggest that the electrical ground layer are split, different ground in the power source end point connection, but this is far from the return path of the signal, the specific application should be how to choose the appropriate method? [A] If you have high frequency > 20MHz signal line, and the length and number are more, then you need at least two layers to this analog high frequency signal. One layer of signal lines, one layer of large area ground, and the signal line layer needs to be punched with enough overholes to ground. The purpose of this is:
For analog signals, this provides a complete transmission medium and impedance matching;
the ground plane isolates the analog signal from other digital signals;
The ground loop is small enough because you hit a lot of vias and the ground is a large plane.

7, [Q] in the circuit board, the signal input plug-in in the left edge of the PCB, mcu in the right, then in the layout is placed near the regulator power chip in the connector (power IC output 5V after a relatively long path to reach the MCU), or the power IC placed in the middle right (power IC output 5V line to reach the MCU is shorter, but the input power line after a relatively long (a section of the PCB)? Or is there a better layout? [A] First of all, is your so-called signal input plug-in an analog device? If it is an analog device, it is recommended that your power supply layout should try not to affect the signal integrity of the analog part. Therefore, there are several points to consider:
First of all, whether your voltage regulator chip is relatively clean, small ripple power supply. The power supply to the analog part of the power supply requirements are relatively high;
Whether the analog part and your MCU is a power supply. In the design of high circuits, it is recommended to separate the power supply for the analog part and the digital part;
The power supply to the digital part needs to be considered to minimize the impact on the analog circuit part.

8, [Q] In the application of high-speed signal chain, for multi-ASIC are present analog ground and digital ground, whether to use ground split, or not split ground? What are the existing guidelines? Which one works better? [A] So far, there is no definite answer. In general you can check the chip manuals. all ADI manuals for hybrid chips recommend you a grounding scheme, some recommend a common ground, some recommend an isolated ground. It depends on the chip design.

9, [Q] When to consider the length of the line? If you want to consider using equal length lines, the difference between the length of the two signal lines should not exceed how much? How to calculate? [A] Differential line calculation ideas: If you pass a sine signal, your length difference is equal to half of its transmission wavelength is, the phase difference is 180 degrees, at which point the two signals are completely canceled. So the length difference at this point is the value. And so on, the signal line difference must be less than this value.
10, [Q] high speed in the snake alignment, suitable for that situation? What are the disadvantages, such as for differential alignment, and requires two groups of signals are orthogonal? [A] snake alignment, because the application of different occasions and with different roles:
If the snake alignment in the computer board, the main role of a filtering inductor and impedance matching, to improve the circuit's anti-interference ability. Computer motherboards in the snake alignment, mainly used in some clock signals, such as PCI-Clk, AGPCIK, IDE, DIMM and other signal lines.
If in the general ordinary PCB board, in addition to the role of filter inductor, but also as a radio antenna inductor coil and so on. Such as 2.4G intercom is used as an inductor.
For some signal wiring length requirements must be strictly equal to the length of the high-speed digital PCB board is to keep the delay difference between the signals in a range to ensure the effectiveness of the data read by the system in the same cycle (delay difference of more than one clock cycle will read the data of the next cycle by mistake). For example, the HUBLink in the INTELHUB architecture, with a total of 13 rods, uses a frequency of 233MHz and requires strict equal length to eliminate the hidden problem caused by time lag, and wire winding is the only solution. The delay difference is generally required to be no more than 1/4 clock cycle, and the delay difference per unit length of the line is also fixed. The delay is related to the line width, line length, copper thickness, and board layer structure, but too long a line will increase the distributed capacitance and distributed inductance, which will degrade the signal quality. So the clock IC pins are generally connected; " end connection, but the snake alignment is not the role of inductance. On the contrary, inductance will make the signal in the rising edge of the higher harmonics phase shift, resulting in deterioration of signal quality, so the snake line spacing is required to be less than twice the line width. The smaller the rise time of the signal, the more susceptible it is to the effects of distributed capacitance and distributed inductance.
The snake alignment acts as an LC filter for the distribution parameters in some special circuits.

11, [Q] in the design of the PCB, how to consider EMC/EMI, what specific aspects need to be considered? What measures to take? [A] good EMI / EMC design must be considered at the beginning of the layout of the device location, PCB stack arrangement, the important linkage method, the choice of devices.
For example, the location of the clock generator as close as possible to the external connector, high-speed signals as far as possible to go inside the layer and pay attention to the characteristic impedance matching and reference layer to reduce reflections, the device pushed by the slope of the signal (slew rate) as small as possible to reduce the high-frequency components, the choice of decoupling (decoupling/bypass) capacitors to pay attention to its frequency response to meet the needs to reduce Power layer noise. In addition, pay attention to the return path of high-frequency signal current so that the loop area is as small as possible (that is, loop impedance loop impedance as small as possible) to reduce radiation, but also the way to control the range of high-frequency noise by dividing the ground layer, the appropriate choice of PCB and shell grounding point.
12, [Q] What do you need to pay attention to the design of the transmission line of the RF broadband circuit PCB? How to set the ground hole of the transmission line is more appropriate, impedance matching is required to design their own or to cooperate with the PCB fabricator?
[A] This issue requires consideration of many factors. For example, the various parameters of the PCB material, the transmission line model based on these parameters, the parameters of the device, etc.. Impedance matching is generally based on the information provided by the manufacturer to design.
13. [Q] When analog and digital circuits coexist, such as half of the FPGA or microcontroller digital circuit part, and the other half is the analog circuit part of the DAC and related amplifier. There are more power supplies of various voltage values, and when it comes to power supplies of voltage values that are used in both digital and analog circuits, is it possible to use a common power supply and what are the techniques in wiring and bead arrangement?
[A] Generally, it is not recommended to use this. This will be more complex to use, it is also difficult to debug.
14, [Q] Hello, please ask in the high-speed multilayer PCB design, the resistors and capacitors and other devices on the basis of the choice of the package, what is the main basis? Those packages are commonly used, can you give a few examples.
[A] 0402 is commonly used in cell phones; 0603 is commonly used in general high-speed signal modules; based on the smaller the package the smaller the parasitic parameters, of course, different manufacturers of the same package in the high-frequency performance is very different. It is recommended that you use high-frequency special components in key locations.

15, [Q] in general in the design of the dual panel is the first signal line or ground line?

[A] This should be a comprehensive consideration. In the first consideration of the layout of the case, consider the alignment

16, [Q] What are the problems that should be paid attention to when designing a high-speed multilayer PCB? Can you do a detailed description of the solution to the problem.
[A] should pay attention to the design of your layer, that is, the signal lines, power lines, ground, control lines, how you are divided in each layer. The general principle is to ensure that the analog signal and analog signal ground at least a separate layer. Power supply is also recommended to use a separate layer.

17、[Q] Is there a strict technical limitation on when to use a 2-layer board, 4-layer board, or 6-layer board? (excluding volume reasons) is the frequency of the CPU or the frequency of its data interaction with external devices prevail?
[A] The use of multilayer boards can first provide a complete ground plane, in addition to providing more signal layers for easy routing. For applications where the CPU is going to control external memory devices, the frequency of interaction should be considered. If the frequency is higher, a complete ground plane must be guaranteed, and in addition, the signal lines should be kept equal in length.

18、[Q] How to analyze the impact of PCB wiring on analog signal transmission, and how to distinguish whether the noise introduced during signal transmission is caused by wiring or op amp devices.
[A] This is difficult to distinguish, only through PCB cabling to minimize the introduction of additional noise cabling.

19, [Q] I recently learned the design of PCB, for high-speed multilayer PCB, power lines, ground and signal lines, the line width is set to how much is appropriate, what is the common setting, can give an example? For example, how to set the operating frequency at 300Mhz?
[A] 300MHz signal must do impedance simulation to calculate the line width and line and ground distance; power lines need to determine the line width according to the size of the current, ground in the mixed signal PCB generally do not use the "line", but the entire plane, so as to ensure that the circuit resistance, and the signal line below a complete plane.

20, [Q] How can the layout to achieve the heat dissipation effect?
[A] There are three main aspects of heat in the PCB:
The heat generation of electronic components;
The heat generated by P c B itself;
Other parts of the heat transfer.
Among these three sources of heat, the heat generated by the components, is the main source of heat, followed by the heat generated by the PCB board, and the heat coming in from outside depends on the overall thermal design of the system and is not considered for the time being. Then the purpose of thermal design is to take appropriate measures and methods to reduce the temperature of components and PCB board temperature, so that the system works properly at the right temperature. This is mainly achieved by reducing heat generation, and accelerating heat dissipation.

21, [Q] Can you explain the relationship between the width of the line and the size of the matching vias?
[A] This is a good question, it is difficult to say that there is a simple proportional relationship, because the simulation of the two is not the same. One is a surface transfer and the other is a loop transfer. You can find a hole impedance calculation software on the Internet, and then keep the impedance of the hole and the transmission line impedance consistent.
22, [Q] in an ordinary PCB board with an MCU control, but no high-current high-speed signal requirements are not very high, then in the PCB around the outside edges of whether to lay a layer of ground to wrap the whole board will be better?
[A] In general, a complete ground can be laid.

23, [Q] 1) I know that the AD conversion chip below to do a single point of analog ground and digital ground connection, but if the board has more than one AD conversion chip case how to deal with it?
(2) multilayer circuit board, multiplexer switch (multiplexer) to switch the analog sampling, like the AD conversion chip need to be separated from the analog part and the digital part?
[A] 
Several ADCs placed together as far as possible, with analog ground digital ground connected at a single point under the ADC;
It depends on the switching speed between MUX and ADC, generally the speed of ADC will be higher than MUX, so it is recommended to put it under the ADC.
Of course, for insurance purposes, you can also put a magnetic bead package under the MUX, debugging depending on the specific circumstances to choose where the single point of connection.

24、[Q] In the conventional network circuit design, some use to connect several ground together, is there such a use? Why? Thank you!
[A] Not quite sure about your question. For a hybrid system there are definitely several types of ground, and they are always connected together at one point, and the purpose of doing so is to equalize the potential. Everyone needs a common ground level for reference.

25, [Q] How can the analog and digital parts, analog and digital grounds in a PCB be handled efficiently?
[A] Analog and digital circuits should be placed in separate areas, so that the return current of the analog circuit in the analog circuit area, digital in the digital area, so that the digital will not affect the analog. Analog ground and digital ground processing starting point is similar, can not let the digital signal reflow to the analog ground.

26, [Q] analog and digital circuits in the PCB board design, what are the differences in the design of the ground? What issues need to pay attention to?
[A] The main requirements of analog circuits on the ground is that complete, small loop, impedance matching. Digital signals have no special requirements if low frequency; if the speed is high, you also need to consider impedance matching and ground integrity.

27、[Q] There are two decoupling capacitors in general, 0.1 and 10, if the area is relatively tight, how to place the two capacitors, which is better to place the back?
[A] According to the specific application and for what chip to design.

28、[Q] Please tell me, in the RF circuit, there are often two signals of IQ, is the length of these two lines need to be the same?
[A] In the RF circuit try to use the same.

29. [Q] Is there any difference between the design of a high-frequency signal circuit and a normal circuit design? Can you briefly explain the alignment design as an example?
[A] high-frequency circuit design to consider the impact of many parameters, in high-frequency signals, many ordinary circuits can ignore the parameters can not be ignored, so you may want to take into account the transmission line effect .

30, [Q] High-speed PCB, wiring process over the hole avoidance how to deal with, what is a good suggestion?
[A] High-speed PCB, less perforation, by increasing the signal layer to solve the need to increase the perforation needs.

31, [Q] PCB board design how to choose the thickness of the power supply alignment? Are there any rules?
[A] can refer to: 0.15 × line width (mm) = A, also need to consider the copper thickness.

32, [Q] digital and analog circuits on the same multilayer board, analog and digital ground to be arranged on different layers?
[A] Do not need to do so, but the analog and digital circuits should be placed separately.

33、[Q] How many vias are suitable for digital signal transmission in general? (The signal below 120Mhz) [A] Do not exceed two vias.

34、[Q] In the circuit that has both analog and digital circuits, how to avoid mutual interference problems when designing PCB boards?
[A] analog circuit if matched with reasonable radiation is very small, generally interfered with. Interference sources from the device, power supply, space and PCB; digital circuits are definitely the source of interference because of the many frequency components. WeChat search public number play embedded. The solution is generally, the layout of reasonable devices, power supply, PCB layering, if the interference characteristics of large or analog part is very sensitive, you can consider using a shield .


35, [Q] for high-speed circuit boards, there may be parasitic parameters everywhere, the face of these parasitic parameters, we are a variety of parameters and then to eliminate, or the use of empirical methods to solve? How should we balance this efficiency and performance problem?
[A] Generally speaking, we should analyze the impact of parasitic parameters on the performance of the circuit. If the impact can not be ignored, it must be considered to solve and eliminate.

36, [Q] multi-layer board layout to pay attention to what matters?
[A] multi-layer board layout, because the power supply and ground layer in the inner layer, be careful not to have a suspended ground plane or power plane, in addition to ensure that the hole hit the ground is indeed connected to the ground plane, is to add some important signals for some test points, to facilitate the measurement of debugging.

37、[Q] How to avoid the crosstalk of high-speed signal?
[A] You can make the signal lines away from some, to avoid taking parallel lines, by laying the ground or adding protection to play a shielding role, and so on.

38、[Q] In the multilayer board design often use the power plane, but in the double-layer board need to design the power plane?
[A] It is difficult, because you have a variety of signal lines in the double layout has been about the same.

39, [Q] PCB board thickness has any effect on the circuit? How is generally selected?
[A] Thickness is more important in impedance matching, PCB manufacturers will ask impedance matching is calculated when the thickness of the board is how much, PCB manufacturers will be made according to your requirements.

40, [Q] The ground plane can make the signal loop, but also and the signal line will produce parasitic capacitance, how should this trade-off?
 [A] depends on whether the parasitic capacitance of the signal has a non-negligible impact. If it is not negligible, it should be reconsidered.

41, [Q] LDO output as a digital power supply or analog power supply means that the digital and analog which first connected to the power supply output is good?
[A] If you want to use an LDO to provide power for digital and analog, it is recommended to connect the analog power supply first, and the analog power supply after LC filtering for the digital power supply.

42. [Q] Should I use a magnetic bead between analog Vcc and digital Vcc, or should I use a magnetic bead between analog ground and digital ground?
[A] Analog VCC is filtered by LC to get digital VCC, and a bead is used between analog ground and digital ground.

43. [Q] How to wire differential signal lines such as LVDS?
[A] Generally need to pay attention to: all wiring including the placement of surrounding devices, ground plane need to be symmetrical.

44、[Q] A good PCB design, you need to do their own as little as possible to the outside of the emission of electromagnetic radiation, but also to prevent external electromagnetic radiation interference with itself, please ask what measures need to be taken to prevent external electromagnetic interference, the circuit?
[A] The method is shielding, to prevent external interference into. Circuit, for example, when there is INA, you need to add RFI filter before INA to filter out RF interference.

45, [Q] using high clock frequency fast IC chip circuit, how to solve the problem of transmission line effect in the PCB board design?
[A] What is this fast integrated circuit chip chip? If it is a digital chip, generally do not have to consider. If it is an analog chip, to see whether the transmission line effect is large enough to affect the performance of the chip .

46, [Q] In a multilayer PCB design, is it still necessary to cover the copper? If the copper should be connected to which layer?
[A] If there is a complete internal ground plane and power plane, then the top and bottom layers can not be coppered.

47, [Q] In high-speed multilayer PCB design, impedance simulation is generally how to carry out, using what software? Are there any special attention to the problem?
[A] You can use Multisim software to simulate the resistor-capacitor effect.

48, [Q] Some devices have thin pins, but the PCB board alignment is thicker, will the connection cause impedance mismatch problem? If so, how to solve?
[A] depends on what the device is. And the impedance of the device is generally given in the datasheet, generally and the pin thickness has little to do with.

49, [Q] differential lines generally need to be equal length if it is really difficult to achieve in LAYOUT, are there other remedies?
[A] can be solved by taking the snake line to solve the problem of equal length, and now most of the PCB software can automatically take the line of equal length, very convenient.

50, [Q] in the chip with a multimeter to measure the analog ground and digital ground interface is on, so the analog region of the digital ground is not multi-point connection?
[A] chip internal ground pins are connected together. However, they still need to be connected on the PCB board. The ideal single-point ground should be to understand the location of the connection points of the analog and digital parts inside the chip, and then the single-point connection location on the PCB board is also designed at the analog and digital demarcation point of the chip.
51, [Q] due to the limitations of the size of the board, my circuit board using two sides of the SMD solder chip, the board goes a lot of over-hole, the signal lines also go near, so the alignment of the signal will be interference?
[A] If it is a low-speed digital signal, should not be a big problem. Otherwise, it will certainly affect the quality of the signal.

52, [Q] digital lines in considering whether to do impedance matching, is to see the signal out to reflect back, the total time is more than 20% of the rising edge, if more than the need for impedance matching. Do you want to impedance match the analog line? How to consider?
[A] Low frequency analog signals do not need to match, RF analog signals of course also need to consider the matching problem.

53, [Q] about the complete ground plane, in the use of AD / DA chip board, if the number of layers, you can provide a complete analog ground and a complete digital ground; can also be divided in the two layers of the ground plane analog ground, digital ground. Which one is better or worse?
[A] Generally speaking, a complete ground plane will be laid. Unless there are some special cases, such as the analog part of the board and the digital part is clearly separated, can be easily distinguished.

54, [Q] When connecting digital and analog ground with magnetic beads or MECCA, it is to use its frequency characteristics so that the high-frequency components in digital ground do not affect the analog ground, while ensuring that the level of the two are equal. So, what is the role of 0ohm resistor to connect digital and analog ground, and sometimes only a small piece of copper is used to connect, can you analyze?
[A] The equivalent circuit of the magnetic beads is equivalent to a band resistance limiter, which only has a significant suppression effect on the noise at a certain frequency point, so when using it, you need to estimate the noise frequency in advance in order to choose the appropriate model. For the case where the frequency is uncertain or unpredictable, the magnetic beads do not fit. 0 ohm resistors are equivalent to a very narrow current path, which can effectively limit the loop current so that the noise is suppressed. The resistor has an attenuation effect in all frequency bands (0ohm resistor also has impedance), which is stronger than magnetic beads. Copper skin is similar to 0ohm resistors.)
55, [Q] How to avoid the noise introduced during wiring?
[A] digital ground and analog ground to a single point of grounding, otherwise the digital ground return current will flow through the analog ground on the analog circuit to cause interference.

56, [Q] PCB how to prevent PWM and other sudden changes in signal interference on the analog signal (such as op-amp), and how to test the size of this interference (radiation interference or conducted interference)? In addition to the layout of the wiring needs to pay attention to, there are no other methods to suppress (in addition to the means of shielding)? [A] To start from several interfaces of the op amp, the input side should prevent spatial coupling interference and PCB crosstalk (layout improvement); the power supply needs different capacitance decoupling capacitors. If the PWM signal is turned into DC control voltage by low-pass filtering, you can consider doing filtering, or connecting a small capacitor in parallel to ground to make the PWM waveform rounded and reduce the high frequency component.

57, [Q] Please, in the board, an ARM or FPGA will often be connected to many RAM, FLAH such devices, please ask these main chips and these memories need to pay attention to what the connection between the number of holes, what is the limit? What is the common size of vias in digital signals? Does the size of the vias have a significant impact on the signal?
[A] If the speed is greater than 100MHz, a signal line should not have more than two vias, and the vias should not be too small, generally, 10 mil aperture can be.

58、[Q] In the cloth double panel (high frequency is), the top ground and the bottom ground connected when the hole is also the less the better? Then how to put the hole is more reasonable?
[A] The hole is less for the signal line, if it is the ground hole, the appropriate more will reduce the ground loop and impedance. The principle is to put in the device.

59. [Q] What should I pay attention to when wiring LVDS signals? How to wire it?
[A] Parallel and equal length.

60、[Q] Is the parallel wiring of data lines for mutual interference?
[A] parallel lines should pay attention to the line and line spacing to prevent crosstalk.

61、[Q] In a 4-layer board, there is a whole acquisition system, with analog amplification, digital acquisition, MCU. after the cloth, how to measure the input impedance of this system, how to do the system input impedance and sensor matching, how to match, there is no relevant design principles?
[A] I don't know how high the frequency of your analog signal is, if it is not high then impedance matching is not needed. Impedance matching can be done by using some simulation software to calculate the impedance of the PCB, such as AppCAD. For example, AppCAD, the impedance of the device can be checked by the manual.

62, [Q] often see a lot of ground holes on the PCB board, the more ground holes is the better? Are there any rules?
[A] Not. To minimize the use of over-hole, in the case of having to use over-hole, also consider reducing the impact of over-hole on the circuit.

63. [Q] Inevitably, there will be cross-plane when wiring multilayer boards. Our current cooking is to try to give priority to the differential lines when cutting the plane without crossing the plane. But some teachers think that single-ended can not cross, the differential is not so strict. Can you tell me what you think about this?
[A] single-ended and differential signals across the ground plane have to return back, if the return flow around a large circle before going back, as well as the induction of more interference in, if the same noise on the differential line, it will cancel each other out, so there is some truth to it.

64, [Q] in the high-speed multilayer PCB design, how to distinguish between digital and analog ground? Is it connected according to the device datasheet?
[A] high-speed design does not need to be divided into digital and analog ground.

65, [Q] How to consider the fusing current of the PCB alignment? How much current PCB alignment will fuse, and what factors are related?
[A] Reference 0.15 × line width (mm) = A, which is the current. Design time can not use the fusing current to do the budget. This is the cross-sectional area of the copper wire.

66、[Q] What protection is needed for the signal input and output interface and power input interface, etc.? When the power supply is 220V input to DC, what protective measures need to be taken in the actual application?
[A] TVS tube, fuse these in the power supply is necessary. Signal, depending on the situation, you also have to add TVS tubes, and diodes to protect the analog circuit input to a large voltage situation.

67, [Q] see PCB board wiring bending 45 degrees and rounded arc, what are the advantages and disadvantages, how to choose?
[A] From the perspective of impedance matching, both lines can be made to match the corner of the bend. But rounded corners may not be processed well.

68, [Q] in the high-frequency alignment if the size is limited, the common alignment method or a reasonable alignment method are those? For example, snake alignment, can it?
[A] Not good, will introduce more parasitic parameters.

69. [Q] When I use the key input model of the instrumentation amplifier, is it still necessary for me to copper-clad the device layer around it? And the instrumentation amplifier feedback resistor I am using a straight plug, the lead is long, replaced by a chip resistor temperature drift and will not meet the requirements, how should I deal with? [A] General instrumentation amplifier chip data will have the recommended Layout method and diagram, you can refer to. Ensure that the leads are short and thick is a must. The choice of chip low resistance or direct insert high resistance which is good, depends on the results of specific debugging.

70, [Q] PCB software can automatically wiring, but the location of the device layout is not to be placed manually? [A] layout wiring are done manually.

71, [Q] in the PCB board making, PCB selection there are no special provisions or general how to select materials? I am now in the production of high-frequency signal circuit board, please ask you to choose what material PCB board is better?
[A] more commonly used in high-frequency circuit board substrate is a fluorine itto dielectric substrate, such as polytetrafluoroethylene (PTFE), usually called Teflon, usually used in more than 5GHz. Do the board with the PCB manufacturer can explain.

72, [Q] I am a beginner in PCB design, I want to understand the selection rules for decoupling capacitors? And the value of the size of how to calculate?
[A] In general, for the power supply part, we should use 10u and 0.1u capacitor to decouple, and consider the decoupling of high frequency and low frequency at the same time; for other original parts, we generally use 0.1u capacitor to decouple in the power supply part.

73, [Q] a 5khz pulse signal in the board after taking 20cm long, 10mil wide alignment, its attenuation can reach how much?
[A] The parasitic parameters of different materials of the PCB are different, you can build a model to calculate according to the parasitic parameters you use.

74, [Q] in the high-frequency microstrip line alignment and the distance between the ground plane have any requirements? For example, greater than 1mm. or not much requirement, as long as it is about the same? Or should we calculate by coplanar waveguide?
[A] must be calculated using coplanar waveguide or microstrip line impedance simulation.

75, [Q] how to wire to minimize the crosstalk between lines of high-frequency signals?
[A] High-frequency signal matching will reduce reflections, and will also reduce radiation.

76、[Q] I would like to ask in the DC-DCConvertIC, in the IC below the need to connect to the ground plane, through Via connected to the ground plane, Via hole number and the degree of influence why?
[A] Generally, we can design according to the reference design. Due to the larger current, a certain number of Via may be required.

77, [Q] impedance matching, if the impedance value given by the pin is complex, that is, there is both impedance part and reactance part, then how to do impedance matching? Consider the resistive part alone?
[A] Consider conjugate matching, the imaginary part of the impedance will be offset.

78、[Q] What kind of concentrated parameters and distributed parameters are better in high frequency? How to choose these two methods are more appropriate? [A] Distributed method, higher, but more complex; set the total way is relatively simple, but there is a certain error.

79, [Q] What are the requirements for the distribution of the upper and lower copper-clad ground of the double-layer board connection over the hole?
[A] Generally speaking, just to improve connectivity, there should not be too many requirements for respectively.

80、[Q] How to balance the parasitic inductance and parasitic capacitance of amplifier input in IF application?
[A] Generally speaking, parasitic inductance and capacitance have a small impact on IF circuits and can be ignored. Just make sure not to introduce large parasitic capacitance and inductance values.

81、[Q] How to effectively reduce the impact of interference between circuit components, and the layout of the amplifier to limit the introduction of ripple suppression?
[A] The principles of reducing interference are
Reduce the radiating end;
Strengthening the isolation, shielding and decoupling of the disturbed;
The principles of ripple reduction are also:
Reduction of ripple output from switching power supplies;
adequate decoupling filtering;

82, [Q] 6-layer design, layer allocation techniques, those alignments to go to the middle layer?
[A] depends on your design. The principle is to ensure that analog signal lines and analog ground has a separate two layers.

83, [Q] in the analog ground and digital ground connected, the method used in the digital ground to connect a suitable bead to the analog ground? And how to choose this bead?
[A] The magnetic bead mainly plays the role of isolation of high frequency noise, different beads filter frequency is different, so according to the noise on the board to choose the right device.

84、[Q] What do you need to pay attention to for the layout of the signal higher than 5G?
[A] both to consider the transmission line effect, but also to consider the parasitic effect, and EMI problems.
85、 [Q] When there are high-speed logic devices in the circuit, what is the wiring length?
[A] The wiring is not afraid of long, afraid of asymmetry or a relatively large difference, which is easy because of the time delay caused by the wrong logic.
86, [Q] in the high-speed digital circuit board, there are a number of different voltage value of the power supply, laying power plane should try to use multi-layer power plane or in the same layer of the power plane on the separate arrangement is good?
[A] can be in a plane of multiple voltages, pay attention to the separation between. You can also take a separate layer of important power supply, so as to ensure that it is not interfered with by other power supplies.

87, [Q] in the walk differential line due to space constraints, can not be completely equidistant and equal length, please ask is equidistant priority or equal length priority?
[A] equal length can ensure impedance matching, but not equally spaced actually have an impact on the differential matching, the need for simulation testing.

88, [Q] In the PCB layout, how to reduce electromagnetic interference? Also which modules should be closer to the main controller chip?
[A] For the main controller, it mainly transmits digital signals, so the analog and power parts should be far away from the controller; for reducing electromagnetic interference, we need to pay attention to matching, decoupling, layout wiring, layering and other issues, we suggest to refer to some information.

89、[Q] When considering the signal integrity, if we only know the frequency of the digital chip is 1GHZ, we generally estimate that its rise time is 1/10 of the cycle, i.e. 0.1ns. What is the basis?
[A] It is a general principle that the speed along depends on the speed of the device output port. If it is too slow it will affect the verdict. Any faster than the chip process can not reach.

90, [Q] Hello, please ask the ARM chip to improve the anti-interference power supply, in addition to the power input access TVS tube, the power input input pin to connect the inductor is better, or magnetic beads is better?
[A] Generally will use magnetic beads.

91, [Q] pcb board online can not be simulated, that is, how to verify that the board has no problems?
[A] Some PCB software can do some alignment checks and integrity analysis, such as cadence.

92, [Q] in the pcb wiring some people in the signal input and output string a resistor for termination, this plays a big role? How to choose this resistor? Those places need to do so?
[A] It depends on the role of the series resistor, some are to play the role of current limiting, some may be to do impedance matching.

93, [Q] What is a good suppression program or into a more systematic approach to the impact of high-speed bursts of power supply?
[A] What you call high-speed bursts, is nothing more than interference signals of different frequencies, using different values of capacitance retirement couples.

94, [Q] High-speed PCBs have any special requirements for the plate?
[A] High-frequency circuits have requirements for PCB materials. In the high frequency to consider the transmission line effect.

95, [Q] on the impedance of the signal line matching, please make a point of introduction and practice?
[A] lower frequency occasions, the need to consider the relationship between the width of the signal line and the carrying capacity of the current, high frequency, the need to consider matching the length of the problem.

96, [Q] What are the anti-interference measures for high-frequency signal lines? Wiring should pay attention to what aspects?
[A] This issue is relatively broad, it is difficult to say in a sentence or two.

97, [Q] why high-speed signals do not need to be divided into digital and analog ground?
[A] Because the driver side can adjust the output phase difference, PCB layout and then adjust it is very difficult to receive the direct input, can not be adjusted.

98, [Q] on the differential line of equal length compensation, why do you directly recommend compensation at the driver side? EricBogatin's book also only gives the conclusion, but no explanation.
[A] Some chips at the driver side have adjustment function, PCB line design is not easy to change, the receiver side of the direct input is generally no delay adjustment function.

99, [Q] in the high frequency selection of board materials, the dielectric constant is not the smaller the better?
[A] It means that the parasitic capacitance is small, however, for the design of the signal line characteristic impedance of the dielectric constant is required, can not be generalized.

100, [Q] What frequency of the crystal to consider the MCU and the crystal alignment?
[A] The crystal and MCU should be as close as possible, with a short straight line connection.

101, [Q] The DC power coming from the switching power supply has a noise of about 100mv, how to effectively filter it out?
[A] You can consider adding modulator LDO products to stabilize the power supply, or consider the appropriate decoupling capacitors to filter out ripple.

102, [Q] analog power supply can also lay the plane, whether and the role of the same ground?
[A] power supply can certainly lay flat. If you can not lay the plane, the power line should be as thick as possible.

103, [Q] please, two-layer circuit board copper, when to choose both sides are covered, when to choose only one side of the copper cladding it?
[A] If you can ensure that one side is a full ground plane, then you can lay only one layer.

104, [Q] In the design of high-frequency (1GHz or higher) board, what are the requirements for the size of the vias and vias spacing? What are the factors that need to be taken into account when matching impedance? Do I need to pay attention to the board material? What are the considerations for the distance between differential alignment and ground plane?
[A] How to take into account the above indicators, it is recommended to do the overall circuit simulation and debugging, parasitic effects will affect the simulation effect, the need for repeated verification and experimentation. 

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