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PCB design tips 100, teach you to master PCB design easily (46-55)
Posted:02:22 PM June 20, 2018 writer: G

In the IBIS 3.2 specification, there is a description of the connector model. EBD models are generally used. If it is a special board, such as a backplane, a SPICE model is required. You can also use the multi-board simulation software (HYPERLYNX or IS_multiboard) to set the distribution parameters of the input connectors when creating a multi-board system, which is usually obtained from the connector manual. Of course, this approach will not be accurate, but it can be within an acceptable range.


47. What are the ways of termination?

Termination (also called matching). The active end match and the end match are generally divided according to the matching location. Wherein, the source termination is generally a series matching of resistors, and the termination matching is generally a parallel matching method. The methods are relatively many, including resistance pull-up, pull-down resistance, David South matching, AC matching, and Schottky diode matching.


48. What is the reason for adopting the termination (matching) method?

The matching method is generally determined by the BUFFER feature, the top case, the level type, and the decision method. The signal duty cycle, system power consumption, etc. must also be considered.


49. What are the rules for using termination (matching)?

The most critical of digital circuits is the timing problem. The purpose of adding matching is to improve the signal quality and get a deterministic signal at the decision moment. For the level-effective signal, the signal quality is stable under the premise of ensuring the establishment and maintenance of the time; for delaying the effective signal, under the premise of guaranteeing the signal monotonicity, the signal change delay speed meets the requirement. Mentor ICX product textbooks have some matching information. In addition, "High Speed Digital design a hand book of blackmagic" has a chapter dedicated to the terminal, from the principle of electromagnetic waves on the role of matching signal integrity, for reference.

 

50. Can I use the device's IBIS model to simulate the logic function of the device? If not, how do you perform circuit-level and system-level simulation?

The IBIS model is a behavioral model and cannot be used for functional simulation. Functional simulation requires the use of SPICE models or other structural-level models.


51. In digital and analog coexisting systems, there are two kinds of processing methods. One is digital and simulation are separated. For example, in the ground, the digital ground is an independent one, and the analog ground is independent. The single point is copper or FB magnetic. Beads are connected, while the power supply is not separated; the other is that the analog power supply and the digital power supply are separately connected with the FB, and the ground is uniformly grounded. Will Mr. Li, whether the effect of these two methods is the same?

It should be said that the principle is the same. Because the power and ground are equivalent to high-frequency signals.

The purpose of distinguishing between the analog and digital parts is to resist interference, which is mainly the interference of the digital circuit to the analog circuit. However, segmentation may cause the signal return path to be incomplete, affect the signal quality of the digital signal, and affect the system EMC quality. Therefore, regardless of which plane is divided, it depends on whether or not the signal return path is increased and how much the return signal interferes with the normal operation signal. There are also mixed designs now, regardless of power supply and ground. In the layout, layouts are separated according to the digital and analog sections to avoid cross-zone signals.


52. Safety Regulations: What is the specific meaning of FCC and EMC?

FCC: federal communication commission

EMC: electro megnetic compatibility electromagnetic compatibility

The FCC is a standards organization and EMC is a standard. The promulgation of the standard has its own reasons, standards and test methods.


53. What is differential wiring?

Differential signals, also known as differential signals, use two identical, opposite-polarity signals to transmit one channel of data, depending on the difference in signal levels. In order to ensure that the two signals are completely consistent, they must be kept in parallel during wiring, and the line width and line spacing remain unchanged.


54. PCB simulation software which?

Many types of simulation, high-speed digital circuit signal integrity analysis (SI) commonly used software icx, signalvision, hyperlynx, XTK, speectraquest and so on. Some also use Hspice.


55. PCB simulation software is how to conduct LAYOUT simulation?

In high-speed digital circuits, in order to improve signal quality and reduce the difficulty of wiring, multilayer boards are generally used to allocate special power layers and strata.

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