Summary: many different types of connectors can be used in high-speed signals. In differential signal and single ended signal applications, the open pin field connector is often the lowest cost connector, and has great flexibility. However, when the signal frequency increases, the connector optimized for single ended signal and differential signal application is more suitable. Although the electrical performance of high-speed signal is very important, when choosing the connection for differential signal
Many different types of connectors can be used in high-speed signals. In differential signal and single ended signal applications, open pin field connector is often the lowest cost connector, and has great flexibility. However, when the signal frequency increases, the connector optimized for single ended signal and differential signal application is more suitable.
Although the electrical performance of high-speed signal is very critical, there are other determinants when choosing the connector for differential signal, such as whether it is easy to implement, whether it is flexible in application, pin density, and cost. When the system designer decides which connector is most suitable for the special application, many aspects that affect the performance of the connector must be considered.
Pin open connector
In general, there are many pins that can be defined arbitrarily. These connectors are made of groups of metal connectors, and the signal pin and ground pin can be defined arbitrarily. System designers can specify the connection they want to achieve acceptable impedance, crosstalk, pin density, etc.
A single ended signal circuit requires a signal path and a return path, or a ground path. Pin strip open connector can be used in such a single ended signal system. Only some pins need to be defined as signal pins and others as ground pins.
The proportion of the number of signal to ground pins in the connector depends on the requirements for signal density and electrical performance. The more ground pins, the better the electrical performance; the advantages of non electrical performance, such as the smaller circuit board space required, come from the example of higher number of signal to ground pins.
Although pin open connector is a low-cost connector, it can also achieve good performance in high-speed system if designed properly. However, its impedance and crosstalk performance may change greatly with the proportion of signal to ground pin.
Pin open connector can be used in single ended and differential signal system. For differential signals, we usually want the maximum coupling between two wires of a pair of differential signals, which means that we should keep this pair of wires as close as possible. However, the coupling between two conductors as a differential pair may be limited by the specific target impedance requirements.
In order to reduce the crosstalk between different differential signal pairs, the coupling between each wire from the signal pair and other adjacent wires must be minimized. It is very important to maintain the electrical balance of the differential pair signal, which can be achieved by ensuring the same degree of routing of the internal signal line of the differential pair and the consistent interaction between each signal line in the differential pair and other adjacent signal lines, shield lines and ground.
Careful use of pin open connector can achieve the above goals, or more complex connector can be used, which will provide better high-speed performance. Such connectors often include complete shielding and ground connections that provide isolation between signals, and also help control impedance.
For extremely high speed performance requirements, the optimized pin open connector can be used in any differential and single ended signal situations. If the signal and ground pin arrangement of pin open connector are defined and fixed in advance, its flexibility will be greatly reduced.
Single ended connector used in differential signal
To some extent, the pin arrangement of some connectors in single ended signal application can be considered as partially definable. The system designer can choose several different schemes to realize the pin arrangement. This kind of connector often has a central connector which plays a role of ground, but there is no pre-defined pin.
Take a connector with 20 pins on each side of the center connector as an example. When all the connector pins are defined as signal pins, the ground center connector provides a unique return path, which can realize 40 single terminal signals in a single connector group.
When the ratio of signal to ground pin is 1:1, each group can realize 20 signal pins (the other 20 pins are used for ground pin). This reduces the effective pin density by half, but provides better high-speed performance. Similarly, when the ratio of signal to ground pin number is 3:1, 30 signal pins can be obtained (the other 10 pins are used for ground pins).
Different signal to ground pin ratio can be mixed in a connector group. For example, some signals may need more isolation from other signals, so different pin ratios can be used between different signals.
When using standard connectors in differential signal applications, there are two logical pin arrangements: all pins are defined as signal pins, or a ground pin is defined in the differential signal pair. When all the signal pins are defined, 20 differential signal pairs can be obtained in each connector group, while only 14 differential signal pairs can be obtained when the ground signal is defined in the differential signal pair.
The main purpose of inserting the ground pin between the differential signal pairs is to reduce crosstalk. At very high frequencies, grounding the extra pins can reduce the impedance of the differential pair to some extent.
Because the additional ground pins reduce the effective density of the pins in the connector, the cost of the connector and PCB will increase. This design will also make PCB routing more complex, although not obvious.
True differential signal connector
In some applications, the real differential signal connector has many advantages, such as reducing load capacitance and improving crosstalk. When some connectors with special definition of pins are used, the wire layout of PCB will be greatly improved, and there is no need to use vias to connect the ground pin pad and the internal layer of circuit board. By removing the unused pins in the differential signal area, the wiring channel between the differential pairs is released, which can provide more flexibility for PCB designers.
But there is also a need to weigh the pros and cons. The signal density in a true differential signal connector is usually lower than the standard connector that fully defines the signal pins. Crosstalk can also be somewhat higher than when using ground connection in a differential signal pair of a standard connector. However, in many applications, the difference of this string is very small.

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