-[Rhett]

Time flies. It's been three years since I first drew the first circuit. When I first started to touch the circuit board, I was full of doubts and some excitement, just like you. On the Internet a lot of hardware circuit experience, knowledge dizzying. Like signal integrity, EMI, PS design will confuse you. Don't worry. Take your time.

Designing hardware circuits, big frames and architectures takes a lot to figure out, but it's not easy to do. Some of the big framework may have their own boss, teachers, they just put the idea of concrete implementation;

But if you're designing your own framework, figure out what you're trying to achieve and see if you can find a reference board that can do the same or similar thing.

If you find a reference design, congratulations, you can save a lot of time (both in early design and in late debugging). Copy right away? NO, let's read and understand it first. On the one hand, it can improve our understanding of the circuit and avoid design mistakes.

First determine the large IC chip, find the datasheet, see whether its key parameters meet their own requirements, what is the key parameters you need, and can read these key parameters, are the hardware engineer's ability to reflect, which also needs to be accumulated over a long period of time. During this period, you should be good at asking questions, because you do not understand something, others often a word can point you, especially the hardware design.

Schematic design is the previous ideas into the circuit schematic. It's very much like the circuitry in our textbook. PCB refers to the actual circuit board, which is converted from the grid table according to the schematic diagram (the grid table is the bridge between the schematic diagram and the PCB), and the packaging of specific components is placed (layout) on the circuit board, and then according to the flying wire (also known as pre-cable) connected to its electrical signals (wiring). After completing the PCB layout and wiring, we should summarize the components to be used, so we will use the BOM table.

In fact, whether using simple protel or complex cadence tools, the hardware design is the same (the operation on protel is similar to windwos, which is post-command; Cadence's product concept & allegro is pre-command, used to protel, suddenly turned to cadence tools, will not be used to this reason).

1) establishment of schematic diagram library. To place a new component on a schematic, we must build a library of modifiers. The library mainly defines the pin definition and its attributes for the new element and represents them in a specific graphical form (we often see a rectangle (for its IC BODY) surrounded by many short lines (for IC pins)). The protel library is extremely simple to create, and because so many people use it, many of the components can be found off the shelf, which is extremely convenient for users. We should make clear the difference between icbody, icpins, inputpin, output pin, analog pin, digital pin and power pin.

2) once you have enough libraries, you can draw pictures on the schematic diagram and connect related components through wire according to the requirements of the datasheet and the system design. Add line and text comments where relevant.

The difference between wire and line is that the former has electrical properties and the latter does not. Wire is good for connecting to the same network, and line is good for annotating graphs. At this point, you should understand some basic concepts, such as wire, line, bus, part, footprint, and so on.

3) after this step, we can generate the netlist, which is the bridge between the schematic diagram and the PCB. Schematic diagram is the form that we can recognize. In order for the computer to convert it into PCB, it must convert the schematic diagram into its recognized form, netlist, and then process and convert it into PCB.

4) get netlist, draw PCB right now? Don't worry. ERC first. ERC is short for electrical code inspection. It can troubleshoot some basic design errors in schematics, such as multiple outputs connected together. (be sure to check your schematics carefully, though, and don't rely too heavily on tools, which don't understand your system, but just sort through it according to a few basic rules.)

6) determine the size of the frame. Draw a frame in the keepout or mechanic area, which will limit the area you need to route. According to the needs of good board length, board width (sometimes, also have to consider the board thickness). Of course, lamination has to be considered. (the meaning of lamination is that there are several layers of the board, how to apply, such as four layers of the board, the top layer of the signal, the first layer of the middle layer of power, the second layer of the middle floor, the bottom signal).

First explain the terminology in (2). Post-command, for example, if we want to copy an object, we should first select the object, then CTRL +C, then CTRL +V. This is the way Windows and protel operate. But concept is another way, which we call pre-command. Again, to copy something, press CTRL +C, select object, and then click outside (copy occurs before object is selected).

1) after determining the board frame, the component layout (placement), the layout of this step is very critical. It often determines the difficulty of later wiring. Which components should be placed on the front, which components should be placed on the back, should be considered. But these are all a matter of opinion; From different angles to consider the placement can be different. In fact, I have drawn the schematic diagram, understand the function of all components, and naturally have a clear understanding of the placement of components (if you ask someone who is not a schematic diagram to place components, the results will often surprise you ^_^). For starters, note the isolation of analog and digital components, as well as the placement of machinery, as well as the topology of the power supply.

2) wiring is next. This is often interactive with the layout. Experienced people often see from the start where the wiring will work. Change the layout if some areas are difficult to wire. For fpga design, the schematic is often changed to make the wiring smoother. Wiring and layout problems involve many factors, and for high-speed digital parts, they are complicated by problems involving signal integrity, which are often difficult to quantify or even quantify to calculate. Therefore, in the case that the signal frequency is not very high, should take the distribution as the first principle.

3) OK? Don't worry, use DRC to check first. This must be checked. DRC will mark the coverage of wiring completion and the places where rules are violated. According to this, they will be checked and amended one by one.

4) some PCB will be coated with copper (which may increase the cost), and the outgoing part will be made into tears (the factory may add them for you). The final PCB file is transferred to the gerber file for PCB production. (some directly to PCB is also ok, the factory will help you transfer gerber).

5) to assemble PCB, prepare bom form, which can be directly exported from schematic diagram. However, it is necessary to pay attention to which parts of the schematic elements should be on and which parts should not be on. For small batches or research boards, it's also easy to manage yourself with excel (large companies often require specialized software). For the novice, the first version is not recommended to directly submit to the assembly factory or welding factory to weld all the bom materials, which is not convenient for troubleshooting. The best way is to prepare your own components according to the bom sheet. Wait until the board came, step by step on the components, debugging.

1) the first step to get the board to do what, do not be in a hurry to see the power supply function, hardware debugging can not be completed in a step of debugging. First take the multimeter to see if the critical network is abnormal, mainly to see whether there is a short circuit between the power supply and the ground (although the manufacturer has done the test for you, this step or to see for yourself, sometimes it seems that some steps are tedious, but can save you a lot of time later!) In fact, short circuit is not only related to PCB, any link in the production may lead to this problem, IO short circuit generally does not cause catastrophic consequences, but the power short circuit......

2) no short circuit in the power network? So good, that is to see the power output is his ideal value, for beginners, debugging the best IC chip, the first to be on the power chip.

3) is the power network short-circuited? This is more troublesome, but to carefully look at their schematic diagram is likely to be such a situation, at the same time, combined with the method of cutting line step by step to find out where the bottom is short circuit, is the problem of PCB (generally worse PCB factory may appear this kind of situation), or assembly problems, or their own design problems. There are some tips on checking for short circuits, which will be issued in the future...

4) the power chip has no output? Check to see if your power chip input is working properly, and check for enable signals, partial voltage resistors, feedback networks...

5) the output value of the power chip is not in the expected range? If you go too far, say 10%, then look at the divider first, these two dividers are usually 1% accuracy, you do this, but also look at the feedback network, it will affect your output power range.

Output jump is normal. That is, grab the power of the moment, look at the power from nothing to the situation (as to why to look at a, hey hey... Professionals still want to see ~)

Undoubtedly, the power supply design is the most important part of the circuit board. The power is unstable. Don't talk about anything else. I don't think balabala tells you how important it is.

In power supply design we use most of the occasion is from a stable "high" voltage to a stable "low" voltage. This is often referred to as dc-dc (DC-DC), and DC-DC with the most used power regulator chip there are two, one is called LDO(low voltage difference linear regulator, we later said linear regulator, also refers to it), the other is called PWM (pulse width modulation switching power supply, we also call it switching power supply in this paper). We often hear that PWM is efficient, but LDO is responsive. Why? Don't worry, let's see how they work.