Q: Understanding modular connectors
The RJ system (Registered Receptacle) has been widely used in the telecommunications and data communications industry since the early 1960s and was classified by the FCC in 1976 as a Registered Receptacle (RJ) system, which standardizes wiring patterns, signal specifications and the physical construction of the connector itself.
Figure 1: Examples of common modular connector types
Common Types
There are a variety of modular connectors on the market for specific applications. The most common connector types and their specifications are as follows.
RJ10 – a simple 4P4C rectangular connector for some telephone handsets
RJ11 – the most common 6P4C for corded telephones, either 6P2C, 6P4C or 6P6C square connectors, used to connect the modem to the telephone line
RJ12 – same size as RJ11, but with 6P6C
DEC MMP/MMJ – smaller version of the RJ11/12 connector, used in American Digital Equipment Corporation equipment
RJ13 – 6P4C, similar to RJ12 type, but with behind-the-wire circuitry
RJ14 – 6P4C with two wires for connecting two telephones or modems
RJ21 – Modular connector containing up to 50 connectors for connecting up to 25 circuits in a large telephone system
RJ22 – similar in shape to RJ11 but with 4P4C, typically used to connect phones
RJ25 – 6P6C, similar to RJ11, but can connect three devices
RJ45 – 8P8C or 8P10C for Ethernet LAN, WAN, WiFi routers, servers, modems, smart TVs, computers, game controllers, industrial/factory automation, IP telephony (VOIP) systems, IoT, microcontrollers, and robots
RJ48 – 8P8C, similar to RJ45, but shielded cable for connecting T1 data lines
Modular connectors can contain 2, 4, 6, 8 or 10 header positions, although not all of these positions are necessarily filled. For example, RJ11 phone connectors typically have 4 or 6 connections, while Ethernet (RJ45 ) connectors have 8 (8P8C) connections.
The standard naming scheme usually defines the wiring of the connector, so a 6P2C connector means – contains 6 positions and 2 connectors, while a 4P4C connector for telephone handset wires contains 4 positions and 4 connectors. While most connectors are used for signal transmission, RJ connector connectors can also be used to provide low voltage AC or DC power.
Additional Features
Modular connectors have many additional features, such as
Shielding , which allows longer cables to avoid electromagnetic interference (EMI) or radio frequency interference (RFI). The widely used shielded RJ45 and RJ48 connectors continue the grounding of the shielding braid on the cable to the panel where the connector is mounted.
Keyed , certified RJ45 connectors employ a tab to stop the connector from being inserted into the socket in the wrong way. This feature is not normally found on standard 8P8C connectors. Color coding can be used to indicate which cables can be used with a particular network connection point.
Mounting options , commonly used options include panel mount, board mount, through-hole mount, and surface mount to PCB. modular receptacles have vertical or horizontal orientation.
Displays and indicators with built-in indications, such as color status LEDs.
High reliability variants that can include EMI/RFI shielding, special keying, protective cover features, and ruggedized products that can support a higher number of insertions and removals.
Sockets with magnetism to improve EMI shielding and connection reliability in xBASE-T networks. These are wire-wound components in the socket that protect against transient energy and provide isolation, signal balancing and impedance matching.
Magnetics can be integrated into Ethernet designs in two ways. The first option is to add a magnetic module to the board between the PHY (Ethernet implementation) chip and the connector socket. The second is to use an RJ45 connector with magnetics integrated into the housing.
Modules tend to be cheaper than integrated devices and can also provide better electrostatic discharge (ESD) protection. RJ45 connectors with integrated magnetics can provide better EMI shielding and more reliable connections. Both strategies have advantages and disadvantages, but magnetics must be considered if wired Ethernet is to be added to the design, as they are part of the Ethernet specification for 10/100/1000 Base-T networks.
Figure 2: Modular connector with integrated magnetism for EMI shielding and connection reliability
Power over Ethernet (PoE) and RJ45
The RJ45 is a type of 8P8C connector. You can plug an 8P8C connector into an RJ45 socket, but you can’t reverse it because a true RJ45 connector comes with a tab that allows the device to be plugged in from only one direction to avoid wiring connection errors.
Modular connectors like the RJ45 also have the ability to relay signals and provide power to the connected devices. Power over Ethernet (PoE) is a technology that provides DC power to devices over unused twisted pairs in the Ethernet cable, thus eliminating the need for separate wiring.PoE is controlled using the IEEE standard 802.3af and subsequent versions that improve power transfer. The different versions include.
The use of PoE is growing rapidly because there is no need for separate cables, outlets or installation costs. The flexibility is very high because the devices do not need to be placed near a power outlet. In addition, their security, reliability and scalability are excellent.
RJ45 connector pinout
The connector uses two RJ45 pinout standards: T568A and T568B. These standards define the arrangement of the eight wires in the connector and each wire must follow a specific color scheme. Both can work in Ethernet
You can choose a specific type based on your design needs and whether you are using straight-through or crossover cable. Straight-through (plug-in cable) has the same wiring standard at both ends. Crossover cables have T568A at one end and T568B at the other end and can be used to connect the same type of device
