-[Rhett]

My understanding: Hardware design is PRS (ProductRequirementSpecification), according to the requirements of the product manager in the COGS (CostofGoodsSale), under the requirements of using the industry mature chip solution or technology, made within the prescribed time in line with the PRS Function (Function), Performance (Performance), the power supply design (PowerSupply), power (PowerConsumption), heat (Thermal/Cooling), Noise, SignalIntegrity, electromagnetic radiation (EMC/EMI), Safety, ComponentSourcing, Reliability, testability (DFT:designfortest), producibility (DFM: designformanufacture), and other required hardware products (note: the product is not the development board).

As you can see, a successful hardware design, the implementation of main functions are only a small part of all links, and basically, implementation of main functions are heavily dependent on chip manufacturers to provide the set of solutions, in general in order to reduce risk, mainly reference set of solutions of reference design, chip makers will provide including device packaging, reference design, simulation model of PCB, reference, etc. All data on the chip function is more and more complex today, hundreds of thousands of PIN, a film easily for a new project, there is no page to read each time the PIN, Specific functions of each input and output, electrical parameters, especially for high-speed design, such as DDR3 interface, XAUI interface and so on. Generally speaking, the reference design provided by chip manufacturers is the best solution for them to develop, verify and test. In many cases, you must follow the reference design, otherwise the hardware may have problems. Generally speaking, it is the signal integrity problem or EMC problem.

Chip manufacturers more and more considerate service, looks hardware engineer HW (HardwareEngineer) value is becoming more and more low, after all the core functions of a product or technology is general in the ASIC or FPGA, HW ICdesign generally don't have the ability for core logic design, after all it is parallel with HW design another job, another is also very complicated work. For this problem, I have also been confused, always feel that there is nothing to do with the hardware design, is not a copy of the reference design, like assembling a computer assembled a single board. Of course, with the increase of project experience, especially in the role of hardware system-level design, I felt that I was thinking more from the perspective of a schematic design engineer. As said at the beginning, a successful hardware design, Function is only a small part, as for other factors and capabilities, the ability of an HW depends on the more factors can be considered, the more in-depth, the better a HW engineer will be.

The main profit of any company that sells hardware products is generally the selling price of COGS, and 90% of COGS depends on the design, and the rest is the production cost. This price is generally more transparent, and there are many OEM factories with fierce competition. Though the design cost 60% also depends on the price of the main chip (this mainly depends on the results of the company top to negotiate with chip manufacturers, HW's role is limited, more is the system engineers can make decisions with what chip conform to product requirements and software functional requirements), but the rest of the resistor, capacitor, inductor, diode, triode, protection device, the interface device, logic chip, logic functions, small chip, power supply circuit are all HW family, of course, there are reference design, but in general reference design in order to better reflect the good performance of the chip, would use one of the more expensive, better performance, This is about combining the company's library of devices to make a choice. My experience is to look at the design of similar products of the company and see what devices are used in the mainstream. After all, for components and components, the price is closely related to the purchase quantity, and the price may vary several times due to different purchase quantity.

It mainly affects two aspects: EMC and Timing. A bad SI design will have strong overshoot over/undershoot and Spike, which will result in the emission of resonant frequency of corresponding frequency N. Bad SI design will lead to High/low instability, or rise/fall time/RisingTime/FallingTime takes too long of the data cycle, or the clock is not stable, which will lead to wrong judgment when sampling Sample at the receiving end. In fact, there will be no error at the receiving end, 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; It is mainly on PCB. Generally speaking, the more layers of PCB, the better SI will be. Of course, there is a trade-off between SI and Cost.

Although generally larger companies have a special Power supply design engineer, but for HW, the basic Power design ability is very important, in truth, any circuit is a kind of Power supply, any circuit problems can be attributed to a Power source, only the understanding for the Power supply circuit, we will be able to understand for circuit board with thorough, especially to the problem of analog circuit can think of to design some simple circuit with analog circuits, rather than FeiLiYong logic circuit to build.

It is mainly for the corresponding specifications of each country (safety regulations as well), and decoupling and filtering are fully considered for all kinds of possible radiation signals. For the eu, it is generally EN55022 / EN55024, and for the us, it is generally FCCPart15. The radiation standards of the eu and the us are slightly different, and the standards of the eu are slightly stricter.

Chip integration is getting higher and higher, the power consumption of a single chip from a few watts to dozens of watts now, cooling is a big problem, and along with the increase of the interface rate, the power consumption of the interface chip is also increasing, resulting in the whole system is: heat! This requires a good consideration of heat dissipation, from the layout of PCB, to the use of Heatsink sink, to the use of fans, there are many considerations.

The device selected by HW must be sourced by the Sourcing department, and the problem of secondsource and leadtime should also be considered in general. It is not possible to select a rare device produced by a small company. In case the device EoL is used, what will you do? Can only modify the design, this loss is big!

Mainly for the consideration of the factory, we must consider the convenience of the production test of the factory, which is convenient for production. If your test is very complex, it will greatly reduce the production capacity and yield of the production line, thus affecting the supply and production of finished products.

For reference design, I feel the most useful places are power supply circuit, decoupling filter circuit and Layout design. As for bus connection, reset circuit, clock circuit, interface circuit, etc., generally speaking, they need to be modified according to the company's device library, design cases and the mainstream devices/schemes in the industry. So do not superstition reference circuit, that is only a reference, too superstitious reference design, they have not figured out the specific functions/parameters of the chip, COPY, even if it can work, there must be a lot of problems in the cost, production.