Learn signal integrity from zero (SIPI) - (1)

Let's start with an introduction , I am a signal integrity engineer （SI The engineer ）, Have worked so far 17 year . I once worked for a well-known communication equipment manufacturer in the world 、 A domestic well-known military enterprise and a domestic well-known chip company , Of course, this 17 I haven't been working on signal integrity all these years , But everything you do is also relevant , done PCB layoutI、SIPI（ Signal integrity 、 Power integrity ） Simulation 、 Have done hardware design 、 Testing and so on , But most of the experience and energy are still in SIPI On .

Of course! , Just after graduation , I'm not doing SI Of , Thanks to an open technology platform , Act as PCB layout The engineer's I can touch SI. I believe there are many PCB layout Engineers are as dissatisfied with the status quo as I was then , So I want to expand my ability 、 Want to improve the treatment 、 Want to learn SI. But it is not as good as the way , Although there are many books on signal integrity that can be referred to , Your son's eyes are full and he has no way to start .

In the next series of sharing, I will introduce how I taught myself SI, And become a signal integrity engineer , I hope I can learn from you SI Of PCB layout Engineers help you . meanwhile , I will try my best to explain it comprehensively SI Some theories of , Of course, it will also be combined with engineering applications , And share what I have done over the years SI Some of my insights . There are inevitably some omissions due to the limited level , It's just for me , Hope to help readers who read my article , I also hope Daniel can give me on-demand , It also enables me to grow in technology .

No more gossip , Cut to the chase . What is signal integrity ？

         Signal integrity （Signal Integrity,SI）, That is what we usually call signal quality . As the signal rate increases , The transmission of digital signals can not only consider the logical realization , We should consider how to make the receiver receive the correct signal waveform . It sounds simple , Signal integrity is the study of how to make the signal transmit correctly between the driver and the receiver . But it contains a wide range of contents , And with the electron 、 The development of communication technology continues to extend to other disciplines , Not only circuits 、 Transmission line theory , It also involves electromagnetic field theory , At the same time, it is also closely related to electromagnetic compatibility .

         Generally speaking, signal integrity generally includes two aspects ： On the one hand, we study the signal transmission , How to optimize the signal transmission path so that the chip at the receiving end can obtain the correct waveform ; On the other hand, study the power supply , That is, how to provide stability for the stable operation of the chip 、 Low noise power supply , Power integrity （Signal Integrity,PI）.

         Generalized signal integrity , It refers to all problems caused by interconnection in circuit design , It mainly studies the interaction between the electrical characteristic parameters of interconnect and the voltage and current waveform of digital signal , How to affect the performance of the product . Mainly in ：

• sequential ： The deviation between the clock signal and the data signal causes that the signal cannot be correctly collected by the clock ;
• Electromagnetic radiation 、 Electromagnetic interference and other external interference make the circuit board work well ;
• Loss attenuation ： There is loss in the transmission channel of the signal , The receiving end has attenuated below the receiving threshold of the receiving chip ;
• Switching noise ： The synchronization of multiple signal lines leads to ground bounce 、 Power rebound , Reduce signal noise and timing margin ;
• crosstalk ： Improper wiring leads to interference between adjacent signals ;
• The signal rings 、 Overshoot ： Impedance mismatch or strong driving capability leads to overshoot and ringing on the received signal ;
• Edge nonmonotonicity ： Edge non monotonicity of clock signal , The clock cannot sample data correctly .
• .......

         Signal integrity analysis is the application of traditional circuit 、 Transmission line 、 Electromagnetics 、 Signals and systems And so on , Solve the problems caused by interconnection in the above circuit design .

         Put it more bluntly , Signal integrity is the study of how to make the signal sent by the driver chip be correctly received by the receiving chip through the transmission channel .

         From this straightforward description , It is not difficult to see that signal integrity contains three elements ：

1. The signal ： Is the subject being transmitted , First of all, we need to understand 、 Be familiar with signal characteristics .
2. chip ： It is divided into driver chip and receiver chip , The signal integrity engineer is to realize the correct transmission of signals between the driver chip and the receiver chip .
3. Transmission channel ： It is the medium for transmitting signals , It is the signal that goes “ road ”. How to realize the correct transmission of signals ？ The signal integrity engineer is required to provide the signal “ Road repair ”、“ Bridging ”.

        

        The road is not well repaired , The signal cannot be correctly received by the receiving chip .

         For board level signal integrity analysis , Got the driver and receiver chips IBIS（ or spice etc. ） Model , The main work is to design the signal transmission channel and build the signal path 、 Bridging , The signal can be sent from the driver chip to the receiver chip smoothly without distortion .（ Signal integrity analysis of the chip , We also need to design the signal channel in the chip and package , Let's just talk about board level , The signal integrity of the package will also be covered later .）

         Due to the different forms of products , The transmission channels of signals are various , Only the centralized form is listed below . Of course , There are many other forms, such as cable transmission 、 Optical fiber transmission, etc , I won't list them one by one here .

         This issue , I first introduced the concept of signal integrity , Later, we will explain how to do signal integrity analysis around the three elements of signal integrity .