The hardware design is based on product manager needs PRS (Product Requirement Specification), in COGS (Cost of Goods Sale) requirements by the industry mature chip solution or technology, complete compliance with PRS function (Function) within the specified time, performance (Performance), the power supply design (power supply), power (power consumption), heat (Thermal / cooling), noise (noise), signal integrity (signal integrity), electromagnetic radiation (EMC / EMI), safety (safety ), purchasing device (Component Sourcing), reliability (reliability), testability (DFT: design for test), manufacturability (DFM: design for manufacture) required hardware products like (note: the product is not a development board) .
You can see that a successful hardware design, to achieve the main function of only a small part in all aspects, but basically, the realization of the main functions of the main chip set solutions rely on chip manufacturers to provide, in general, in order to reduce risk, the main reference is the reference design program complete chip set, chip manufacturers will provide all the information, including device package, reference design, simulation models, PCB reference, etc., in today's increasingly complex chip function, a film on a few hundred at every turn one thousand PIN, for a new project, it is not the time to thoroughly understand the pages of each PIN, the specific function of each input and output, electrical parameters, especially for high-speed designs, such as DDR3 interfaces, XAUI interfaces and so on. Generally chip manufacturers to provide reference designs is that they go through development, validation, testing the best solution in many cases is that you have to do in accordance with the reference design, or may have a hardware problem, in general, is the signal integrity problems or EMC problems.
Chip manufacturers to provide more attentive service, look Hardware Engineer HW (Hardware Engineer) worth less and less, after all, a product of the core features or technology in general are inside the FPGA or ASIC, HW generally do not have the ability to carry out core logic design IC design, after all, this is a parallel design with HW another job, another very complex task. For that matter, I have also been confused, always I feel there is nothing to do hardware design of, and not that copy copy reference design, just to assemble a computer, like a veneer assembling thing.
Of course, with the increase of project experience, especially in the role of system-level design of the hardware now, I realize I feel more considered from the perspective of a schematic design engineers to consider the issue. Like said at the beginning, a successful hardware design, function Function only a small part, as to other factors and capabilities, the ability of a HW depends on more factors to consider, the more in-depth, the more is a good HW engineer.
1. Cost Cost of hardware products to sell any of the company's main profit in general is the sales price -COGS, while COGS90% depending on the design, the rest is the cost of production, the price in general more transparent, there are many foundries, intense competition. Although 60% of design costs also depend on the price of the main chip (the result of high-level negotiations with the major chip manufacturers rely on the company, the limited role of HW, systems engineer to make decisions more is what chip can meet the demand for products with features and software demand), but the rest of resistors, capacitors, inductors, diodes, transistors, protection devices, interface devices, logic chips, the logic function, a small chip, the power supply circuit HW are all the shots, the reference design of course, but in general reference in order to design better reflect the good performance of the chip, the general will choose more expensive, the better the performance of the device, which would be combined with the company's devices to choose a library. My experience is to see more similar products design company, we look at what is mainstream devices, after all, for components, the amount of the purchase price with a great relationship, due to the different purchases prices may differ several times.
2.2 Signal Integrity Signal Integrity two main effects: EMC and timing Timing, SI poor design will have a strong overshoot over / undershoot, a spike Spike, which causes emission resonance frequency corresponding to a frequency N; bad SI design will lead to High / low unstable or rise / fall time rising time / Falling time accounting data period is too long, or the clock is unstable, would cause erroneous sampling at the receiving end determines sample, in fact, not a receiving end wrong, just wrong signal. SI design schematic designs, mainly from the impedance (series resistance) for the settlement, with appropriate decoupling filter capacitor; now mainly in the PCB, the more layers of PCB in general, will be better SI of course there were a trade-off to keep the Cost.
3.3 Power Supply Power Supply Although some large companies generally have a dedicated power supply design engineers, but for HW, the basic design of Power capacity is still very important, from the truth, it is a kind of power any circuit, any circuit the problem can be attributed to one power supply problem, only for in-depth understanding of the power supply circuit to the circuit board with in-depth understanding, especially for analog circuit problems can think of using some simple analog circuit design circuit, instead of laboriously logic circuit to ride.
4.4 Safety Safety for the interface circuit, the main costs are the safety devices, this interface is actually going much anti-voltage, current strike? It is necessary to carefully consider what the device, fuse? PTC? TVS? High-voltage capacitors?
5.5 electromagnetic compatibility signal EMC / EMI is mainly directed against the corresponding specifications of each country (also a safety), for a variety of possible radiation are fully prepared with decoupling, filtering, for the EU generally EN55022 / EN55024, the US general is FCC Part 15, the EU and US radiation standards are slightly different, slightly more stringent EU standards.
6.6 Power (Power Consumption) now promote environmental protection, but also operators, HW power must also be considered, such as a power supply circuit with a higher efficiency, with the LDO PWM alternative, more efficient conversion topologies.
7.7 heat dissipation (Thermal / Cooling) chip more integrated, single-chip power from a few watts to tens of watts now, the heat is a big problem, but along with the increase rate of the interface, the interface chip power consumption to improve, causing the entire system is: This requires carefully consider the heat dissipation problem, from the layout of the PCB, to the use of a heat sink heatsink, to the use of a fan, there is a lot to consider!.
8.8 Noise (Noise) cooling fan is the best way, but the problem is caused by noise, ITU for noise communication devices also have a clear specification, which requires balancing the number of fans, speed, wind direction, control and other factors.
9.9 Device Procurement (Component Sourcing) HW selection of devices have to be able to purchase the Sourcing department, and generally also consider second source of problems, and problems of lead time, we can not say that only a small selection of a company's production of rare device, in case this EoL devices, and how did you do? you can only modify the design, which lost big!
numerical 10.10 reliability (reliability) overall system MTBF how much? What devices are most at risk? work each device Margin What percent?
11.11 testability (DFT: design for test) / manufacturability (DFM: design for manufacture) aimed at considering the plant, must take into account the convenience of factory production test, to facilitate the production, if your testing is complex, it would greatly reduce the productivity and yield of the production line, thereby affecting the supply and production of finished products. For reference design, I feel the most useful place mainly power supply circuit, a filter circuit, and decoupling Layout design, as for the bus connection, a reset circuit, clock circuit, interface circuit, etc., generally require device according to the company database design case and the industry's mainstream devices / programs to be modified. So do not superstitious reference circuit, it is just a reference, the reference design blindly believe that he did not find out the specific chip features / parameters of it, come on COPY, even if they can work, certainly in terms of cost, production has many problems.