A successful hardware design, to achieve the main function is only a small part of all links, and basically, to achieve the main function of the main chip set solution rely on the chip manufacturers, generally in order to reduce the risk, is the main reference sets reference for the design, chip manufacturers will also provide devices including package, reference design, simulation model, PCB reference and so on all the information.
The main profit of any company that sells hardware products is generally the selling price -COGS, while the COGS90% depends on the design, and the rest is the production cost. The price is generally transparent, and the factory is also many, and the competition is fierce. Although the design cost also depends on 60% main chip prices (mainly rely on the company executives with chip manufacturers the outcome of the negotiations, the role of HW is limited, more system engineers do what decisions with the chip can meet the requirement of software and functional requirements of the product), but the rest of the resistor, capacitor, inductor, diode, triode. Protection device, interface device, logic chip, logic function, small chip, power supply circuit are all HW decisions, of course reference design, but in general in order to better reflect the good performance of the reference design chip, generally choose more expensive, better device performance, it is necessary to combine the company's choice of the library. My experience is to see more about the similar product design of the company, and see what devices are used by the mainstream. After all, for the components, the price is very related to the purchase quantity. The price of the different purchases may vary several times.
Signal integrity Signal Interity:
Two main effects: EMC and timing Timing, SI design is not good may overshoot over/undershoot, strong peak Spike, this will cause the corresponding frequency of the resonant frequency of the N emission; SI bad design will lead to instability of the High/low, or the rise time / fall time Rising Time/ Falling Time data for the cycle is too long, or the clock is not stable, will lead to incorrect judgment, at the receiving end of sampling Sample in fact, the receiver can not go wrong, but the error signal. SI design in schematic design, mainly from impedance matching (serial resistance) to solve, coupled with the appropriate decoupling filter capacitor, and mainly on the PCB, generally speaking, the more the number of PCB layers, SI will be better, of course, here is a trade-off with Cost.
Power design Power Supply:
Although generally larger companies have special power supply design engineer, but for HW, Power basic design ability is very important, from the truth, any circuit is a power supply circuit, any problems can be attributed to a power supply circuit, only for understanding, to with the in-depth understanding of the circuit board, especially for analog circuits, analog circuit design can come up with some simple circuits, instead of trying to take the logic circuit.
Safety regulation Safety:
For the interface circuit, the main cost is in relation to the safety devices. How long does the interface resist large voltage and current blow? So we need to consider what devices we use, fuse? PTC? TVS?
Mainly for the corresponding norms in various countries (safety, too) signals for a variety of possible radiation are fully taken into account the good decoupling, filtering, for the European Union is generally EN55022/EN55024, for the United States is generally FCC Part 15 emission standard for the European Union and the United States is slightly different, slightly strict EU standards.
Power Power Consumption:
Now all advocate environmental protection, operators also, HW must also consider the power saving, such as the use of more efficient power circuit, PWM instead of LDO, the more efficient conversion topology.
Heat dissipation Thermal/Cooling:
The integration of more and more high, single chip power from a few watts to tens of Watts now, heat dissipation is a big problem, and with the increase in the rate of power interface, interface chip is also improved, the entire system is hot! It needs to consider the heat problem, from the layout of PCB, use the to the Heatsink heat sink, fan to use, there are a lot of consideration.
For the reference design, I feel the most useful place is the main power supply circuit, filter circuit and Layout decoupling design for bus connection, reset circuit, clock circuit, interface circuit and so on, are generally required according to the company's device design case library, as well as the industry main stream device / amend. So don't superstition the reference circuit. It's only a reference. Too much superstition, reference design has not yet made clear the specific functions and parameters of the chip itself. If COPY comes over, even if it works, there must be many problems in terms of production cost.