If you can't pick up the schematic and know what to do and how to do it, then you have not really completed the designer's work.

The more information you can clearly convey in the schematic diagram, the more easily everyone's life can be.

In the first column of my mixed signal PCB design, we solved this problem: what is it? In my second column -what makes it difficult (uh)? - We consider it. What makes the hybrid signal PCB design more challenging than pure simulation or pure digital PCB design.

Therefore, since we have defined this topic, we want to talk about some things that we can do at the design of the design schematic as a designer in order to more clearly convey our design intentions to those who may inherit this job in the future. In the life cycle.

The purpose of the schematic diagram ...

In order to truly understand what we express in this blog post, we must all have a common understanding of the purpose of the schematic diagram for the purpose of this blog post. Or, maybe a better expression is: as a designer, what do we want to be the schematic, and what do we do for us when recording our design intent?

Communication function: So far, the most important thing for the schematic diagram is to clearly convey the function of your design. If you can't pick up the schematic and know what to do and how to do it, then you have not really completed the designer's work.

A good method is to use the first frame diagram, which shows how each part of your design interacts with the basic connection level. Below we see a good example from the Terasic development board DE0-NANO-SOC.

Observe how to have enough details to let you know how things are connected, what is on the board, and how everything is connected. This is a very good example worth learning.

Drives unique information or special information specific to design: We mean here that you must convey the details specific to the design in the schematic diagram. A good example that we may be familiar with is a variety of functions on the microprocessor.

In other words, if you connect the GPIO pin of the microprocessor as GPIO, please name it accordingly! If you use the GPIO pin as part of the I2C bus, please name it appropriately! For example, it may be "I2C-SDA ", Not just" GPIO16 ".

By putting all possible functions of each pin, some operations can be simplified from the creation stage of the principle diagram. Yes, it takes time, but it can make the schematic more clear!

Another good method is to use additional text, pictures, and charts to enrich your schematic diagram! It is always a good thing to add key information to your schematic diagram, even if this means to use additional one (or two or two (two or two two Zhang or three pieces) Come on this paper.

The following is a few examples in our own schematic diagram. In one example, we show the configuration mode of the Ethernet PHY bias; on the other hand, we show the switch status required to simulate the front end of the multiple input range. By putting this information on the schematic diagram, you will save you (and your colleagues) and let anyone who read it know the intention.

Mixed signal schematic information ...

Okay, but what does this mean for hybrid signal PCB? What kind of information is very important, especially in the design of the hybrid signal? We are glad that you ask ...

Multiple GND/Return: Sometimes as designers, you will use multiple GND/back to the network in the design. Maybe you have an isolation circuit, a sensitive thermocouple regulating circuit, a power circuit of a high -power switch mode or a local PLL power supply and circuit network.

If this is what you find yourself in design, let yourself (and other people!) Easy, and appropriately name these back networks! Is it more clear to use different symbols? Maybe. Is the use of different symbols and unique names (such as "PLL-RTN", "PGND", "agng" or "ISO-GND") is more clear? Absolutely!

But what is the meaning of this? All these additional work typing and naming networks ... Who has time? The question is that most experienced engineers will appreciate this -it tells them that returning to the plane to be isolated or cut off is for a reason. And there are sufficient reasons. It tells the engineer who is going to use this schematic. You are paying attention to details. Moreover, it will convey such a fact that there is a reason even if you use multiple returns to the network, not just because you have risen for a while. It shows that these networks aims to provide specific functions and help the separation circuit return paths, which is very important in the design of hybrid signal.

Multiple branches from the power network: Since you may often use multiple power to return the path in the design, you may also need to use multiple power paths. Sometimes these paths are not at different voltage levels, but may only be isolated from high -frequency power supply on the circuit. A good example is a highly integrated DSP, which has internal ADC and DAC devices.

You may want to save circuit board space and cost by using the same VCC power supply as the reference voltage of these converters -this is what designers often do -but if you do not clearly name these VCC networks, it may cause confusion to confuse confusion Essence

For example, please consider the following:

· 2V5

· 2V5-1

· 2V5-2

· 2V5-3

Of course, when you first capture the schematic diagram, you may be able to track things in this way, but it may soon lose control. Later, when you make a PCB layout, forget it -you turn it in place and try to track the naming "convention".

Compare the previous example with the following example:

· 2V5

· 2V5-ADC-VREF

· 2V5-DAC-VREF

· 2V5-Locking Ring Ring

We will leave you to decide which is clearer and more effectively convey the design intent.

Decoupling capacitor: Sometimes on the schematic diagram, it is difficult to place a capacitor on each pin, even if this is what you want to complete in the layout. The use of some simple text comments here can produce great differences, and it is very helpful for anyone who performs PCB layout. It can simply say:

Place (1) 10UF and (1) 0.1UF near each VCC pin

... near a set of 40 capacitors for FPGA's 20 pins.

The decoupling in the design of the hybrid signal may be tricky. The more you can convey the design intentions you have achieved hard work, the better the product will be. Combining the annotation on the schematic with the unique network name and the return path can greatly help keep all the circuits in the design in a good state and work in the way you want.

Simulation circuit notes: This is quite easy to do, and can add a lot of content to the level level level. For example, if you spend a few hours of fine -tuning the amplifier filter, you can add some comments to the appropriate position of the schematic diagram so that it is easier to understand the function without starting the SPICE simulator. Some simulated filtering structures are complicated, unless you live in that world, most engineers will not put it at the forefront of the brain.

Simply write some like ...

'Third -order Batworth low -pass filter, 500kHz -3DB'

… It means that junior engineers and others who may not be a master can watch this module and say, "Well, I may not know how to design one of them, but at least I know what it should do." Only own this level available available available. Information is more important than many of us realized, which is what we usually think of granted.

Even if it is just the gain of the circuit and the expected output scope, it is very valuable for the debugging of software engineers or technicians who may not have many design experience. We find it useful for our own design. Sometimes there are too many things that you have forgotten some details; it doesn't matter, but if you write things down, you will avoid a lot of pain in the future.

in conclusion

I believe you have already begun to understand: the more useful information you contain in the schematic diagram, the better. For a variety of reasons, this information may be beneficial. For example, it can help software engineers understand how you want the chip to be biased when starting, or it can tell them the address of the I2C device. The technical personnel who execute the workbench may be interested in it and tell them what you want the output voltage range on some pins, where should certain components be placed physically, or what the circuit block should do.

All these are suitable for any design, but due to the complexity of the beast, it becomes more important in the mixed signal design than ever before! Multiple supply paths and return paths; integrated ASIC, data converter and power converter; The list is endless. However, the more information you can clearly convey in the schematic diagram, the easier your life will become with your designs from the idea to the progress of the product.