Some notes on electronic design

Today's society cannot function without various electronic products, so do you know what precautions should be taken in electronic design? Doing electronic engineering design requires careful consideration and careful consideration to avoid mistakes as much as possible. However, for novices who are just getting started, it is often difficult to be foolproof, and there will always be times when they cannot be considered. For example, the following misunderstandings are pitfalls that many electronic novices have encountered. Learn more about them to avoid making the same mistakes again.

Relying on hardware alone to reduce power consumption?

In the process of hardware circuit or chip design, we pay great attention to one concept, which is reducing power consumption! Power consumption control is indeed a key part of hardware design, especially in consumer electronics products. Many consumer electronic products are equipped with batteries, such as Bluetooth headsets, smart impressions, etc. Batteries have always been a pain point in such electronic products, so power consumption is an important indicator in terms of product competitiveness. However, is power saving only something that hardware designers should consider? The answer is: No! In fact, software control also has a lot of emphasis on saving power. In the circuit system, the most power-consuming ones are memory access, bus requests, and CPU. Operations such as running are controlled by software. An excellent software program should be strictly controlled to avoid frequently triggering these power-consuming actions. This will greatly contribute to reducing the power consumption of the entire product!

Must overshoot signals be eliminated with matching resistors?

First, let’s explain what the overshoot phenomenon is. Anyone who has used a microcontroller should have tried to let the IO of the microcontroller output some signals. For example, when driving a buzzer, directly use IO to push a fixed frequency square wave. At this time, if you use an oscilloscope to capture the IO output signal, you can find that the signal is not as clean as the square wave drawn in the book. It will have some burr-like things on the edge of the signal flip, and you will see upward burrs on the rising edge. , there will be a downward burr on the falling edge. This glitch is an overshoot phenomenon, which is caused by the electrical characteristics of the IO itself. The overshoot phenomenon can be filtered out by adding a matching resistor through an external circuit, but this is not always necessary for overshoot. The reason is that if you want to completely eliminate the overshoot phenomenon, you may need a relatively large resistor, and at the same time ensure that the voltage amplitude of the signal is acceptable, the current will be much larger at this time. Therefore, sometimes as long as the overshoot phenomenon is within the acceptable range, there is no need to completely eliminate the overshoot.

Memory chip select grounded?

Memories basically have a chip select signal. Generally, when the bus needs to access stored data, the chip select signal CS will be pulled low to a valid state. Some people may ask, in order to reduce the control signal lines, and knowing that the system itself will frequently access the memory, can the chip select be directly grounded so that it is always selected? In fact, there is no problem with the function, and it can be always selected. However, the power consumption of most memories will be much greater when chip select is active, reaching more than 100 times. So it is better to use the CS signal to control the memory and select it only when access is needed.

Are FPGA logic gates a waste if they are idle?

Nowadays, FPGA has more and more logic resources, which is undoubtedly a good thing for engineering developers. Because there are more resources at your disposal, there is more space for you to play. The key is to write code without thinking about saving resources all the time. However, for applications with relatively high power consumption requirements, it is still necessary to save logic gate resources as much as possible. Because in FPGA, the power consumption during operation is proportional to the number of logic gates used internally and the number of flip-flops of flip-flops. Therefore, the resources used in the digital circuit and the flip frequency should be reduced as much as possible, and flipping is prohibited when flipping is not needed. Will effectively reduce power consumption.

Just leave the unused chip IO floating?

An obvious disadvantage of floating IO is that the internal signals of the chip are easily affected, because the floating IO is easily interfered by external influences and forms oscillation signals that are transmitted to the inside of the chip. Some people say that it is enough to add a pull-up resistor to fix its state, right? Adding a pull-up resistor can solve the interference problem, but it will also introduce power consumption problems, not much, probably a microampere level current consumption. The best way to deal with it is to set the IO to the output state, which can not only fix the state but also avoid the loss of power consumption.

PCB using automatic routing?

Engineers with a little experience in electronic design should not use automatic routing, but beginners may use the automatic routing function directly for convenience. Here is an introduction to the disadvantages of automatic wiring. On the one hand, automatic wiring will consume a relatively large area. At the same time, the software will automatically generate a lot of vias. Too many wirings and vias will affect the final mass production cost of the PCB. and performance. Therefore, no one will use the automatic routing function when developing real products. They basically pull the wires manually, route the wires according to the signal characteristics as much as possible, and set parameters such as line width and copper pouring.

The points introduced above are things that many novice engineers fail to consider when designing. Electronic design requires slowly accumulating experience in practice. It is also very important to learn from the experience of others. This can reduce the cost you pay in the process of trial and error. Price! The above are some precautions for electronic design, I believe it will be of some help to you.