In my work, I often encounter people asking what is a high-speed circuit, or what to pay attention to when designing a high-speed circuit. Whenever you encounter this kind of problem, you get confused. In fact, different products and different people have different understandings of it. Today, I will briefly summarize some basic concepts, including the understanding of high-speed circuits, what is signal integrity and signal bandwidth.
1、 Definition of high speed circuit
I have seen many definitions of high-speed circuits from various materials and books. Different products may have different definitions of high-speed signals. The specific definition depends on the type of product designed. The simple sorting mainly includes the following:
1.1. It refers to the circuit in which the analog characteristics in the circuit, such as the inductance and capacitance of the wire, work due to the high-speed change of the signal.
1.2. The working frequency of the signal exceeds 50MHz, and the circuit above this frequency has accounted for a considerable part of the whole electronic system.
1.3. It is defined according to the time of the rising edge and falling edge of the signal.
1.4. The layout of G transmission rate on DDR, SerDes, UFS, etc., which you are usually familiar with
2、 Signal integrity problem
The requirement of signal integrity is that the signal arrives at the receiving end with the correct timing, amplitude and phase from the sending end to the interconnection transmission process, and the receiving end can work normally, or it can be said that the signal can well maintain the characteristics of time domain and frequency domain in the interconnection transmission. There are usually two definitions:
2.1 When the edge time of the signal is less than 4-6 times the interconnection transmission delay, the integrity of the signal needs to be considered.
2.2 when the line propagation delay is greater than the rising edge or falling edge of the driving end, it will cause unexpected results of transmission.
2.3 let‘s briefly talk about the relationship between time domain and frequency domain, because I was confused when I came into contact with these two concepts:
The above materials mainly refer to cadence high speed circuit design and ANSYS signal integrity analysis and simulation examples
If there are similarities or errors, I hope you will leave a message to correct, thank you!!
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