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hardware design is based on the needs of the product manager PRS (Product Requirement specification), at the request of COGS (cost of Goods Sale), uses the current industry-proven chip scheme or technology to complete the PRS function within the specified time, performance (performance), Power supply design (power supply), power consumption (power consumption), heat dissipation (thermal/cooling), Noise (Noise), signal integrity (Signal Integrity), electromagnetic radiation (Emc/emi), EE (Safety), device sourcing (Component Sourcing), Reliability (reliability), testability (dft:design for test), productive (dfm:design for manufacture) and other required hardware products (note: The product is not a development Board).
It can be seen that a successful hardware design, the main function of the implementation is only a small part of all aspects, and basically, the main function of the implementation is mainly based on chip manufacturers to provide the package, in general, in order to reduce the risk, mainly refer to the reference set of the design of the project to complete, Chip manufacturers will also provide including device encapsulation, reference design, simulation model,PCB reference and so on all the information, in the chip function more and more complex today, a film is still hundreds of thousands of pin, for a new project, is no time page to thoroughly understand each pin, The specific functions of each input and output, electrical parameters, especially for high-speed design, such as DDR3 interface, XAUI interface and so on. In general, the chip manufacturers provide reference design is their development, validation, testing the best solution, in many cases you have to follow the reference design, otherwise the hardware may be a problem, in general, signal integrity problems or EMC problems.
chip manufacturers to provide more and more attentive service, looks like hardware engineer HW (Hardware Engineer) value is getting lower, after all, a product of the core function or technology is generally in the ASIC or FPGA, HW generally do not have the ability to design the core logic IC, after all, this is a parallel with the HW design, another work, Another very complicated task. For this problem, I have also been confused, always feel that hardware design is nothing good, not to copy reference design, and assemble a computer like a single board.
of course, with the increase in project experience, especially in the current hardware system-level design role, I feel that the original consideration is more from a schematic design engineer's point of view. as you start to say, a successful hardware design, functional function is only a small part, as for other factors and abilities, a HW capability depends on the more factors that can be considered, the more deeply it is, the more an excellent HW engineer.
1 cost costs any one of the companies selling hardware products, the main profit is generally the sales price -cogs, and cogs90% depends on the design, the remaining is the production cost, the price is generally more transparent, the factory is also a lot of competition is fierce. Although the design cost of 60% also depends on the price of the main chip (this mainly depends on the company's high-level and chip manufacturers to negotiate the results, the role of HW is limited, more is the system engineer to make decisions with what chip can meet product requirements and software function needs), but the remaining resistors, capacitors, inductors, diodes, transistors, protection devices , interface devices, logic chips, logic functions, small chips, power circuits are all HW decision-making, of course, reference design, but generally referred to the design in order to better reflect the good performance of the chip, the general will choose more expensive, better performance devices, which will be combined with the company's device library to choose. My experience is to look at the company's similar product design, to see what the mainstream is the device, after all, for the components, the price with the purchase amount has a great relationship, different purchase volume caused by the price may be several times.
2.2 Signal Integrity Signal Integrity mainly affect two aspects:EMC and timing timing, bad si design will have a strong overshoot over/undershoot, Spike Spike, This results in the transmission of the corresponding frequency n resonant frequency; bad si design can lead to high/low instability, or rise/fall time rising time/falling time is too long for the data period, or clock instability, will lead to sampling at the receiving end of the sample error , in fact, there is no error on the receiving side, only the signal is wrong. Si design in the schematic design, mainly from the impedance matching (serial resistance) to solve, supplemented by the appropriate decoupling filter capacitance; With the main PCB, in general, the more PCB layer, SI will be better, of course, here to go with the cost of a trade-offs.
3.3 power supply design power supply Although the larger companies have specialized power design engineers, the basic power design capability is important for HW, and in principle, any circuit is a power source, Any circuit problem can be attributed to a power supply problem, only for the power circuit understanding in depth, in order to understand the circuit board and in depth, especially for analog circuit problems, can think of analog circuit to design some simple circuit, rather than laborious with logic circuit to build.
4.4 Safety Regulation Safety for the interface circuit, the main cost is in with the safety device, the interface is to resist how much voltage, current strike ? This is going to take a good look at what device, fuse? Ptc? TVS? High Voltage capacitors?
5.5 Electromagnetic compatibility Emc/emi is mainly for each country's corresponding norms (safety regulations are also), for a variety of possible radiation signals are fully considered decoupling, filtering, for the European Union is generally en55022/en55024, For the United States is generally the FCC Part 15, the European Union and the United States radiation standards slightly different, the EU standards are slightly stricter.
6.6 Power consumption (power consumption) is now all about environmental protection, operators also,HW must also consider power-saving, such as the use of more efficient power circuit, PWM replacement Ldo, more efficient conversion topology.
7.7 Cooling (thermal/cooling) chip integration more and more high, single-chip power consumption from a few watts to the present dozens of watts, heat dissipation is a big problem, and with the speed of the interface increases, the interface chip power consumption is also increasing, resulting in the entire system is: thermal this need to consider the thermal problem, from the layout of the PCB, to the use of heat sink heatsink, to the use of fans, there are many considerations.
8.8 Noise (Noise) fan is the best way to dissipate heat, but the problem is the noise,the ITU for communication equipment Noise also has a clear specification, this need to balance the number of fans, speed, wind direction, control and other factors.
9.9 Device Sourcing (Component Sourcing) HW-selected devices must be procured by the Sourcing department and generally take into account the problem of second source, and lead time, Can't say to choose a rare device that only a small company produces, in case the device EOL, what do you do? You can only modify the design, which is a big loss!
10.10 Reliability (reliability) What is the value of the entire system MTBF? What is the most risky device? What is the percentage of work margin per device?
11.11 testability (dft:design for test)/productive (dfm:design for manufacture) is mainly for factory consideration, must take into account the convenience of factory production testing, convenient production, If your test is complex, it will greatly reduce the production line capacity and yield, thus affecting the supply and production of finished products. For reference design, I feel the most useful place is mainly power supply circuit, decoupling filter circuit and layout design, as for the bus connection, reset circuit, clock circuit, interface circuit and so on, in general, according to the company's device library, design cases and the industry mainstream devices/programs to be modified. So do not superstition reference circuit, that is only reference, too superstitious reference design, I have not yet figured out the specific features/parameters of the chip, copy over, even if it can work, certainly in terms of cost, production has many problems.
HW Responsibility (Hardware Engineer)
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