Backplane connectors: What are they and how are they used?

Often referred to simply as a backplane, this special type of printed circuit board is used as a support structure for connecting other PCBs. The backplane connector adds mechanical strength and stability while also acting as a plane for integrating other system components called daughterboards.

Daughterboards are connected to the backplane to perform different functions. The easy interchangeability of different cards is one of the reasons backplane connectors are so versatile and so widely used. Scalability, modularity and ease of use make backplane connectors a popular choice for people designing custom computer systems. Not to be confused with motherboards, backplanes do not have active components like microprocessors. The common misconception likely stems from backplane connectors being connected to single board computers or system host boards. At which point, the system does function like a motherboard.

If backplane connectors have design shortcomings it’s in dealing signal quality. When a signal enters a system from an external server, it first travels through traces on a daughter card, then into the backplane connector. The backplane connector directs the signal accordingly to the output. It is when our ever-increasing need for speed rushes the job that we run into problems! Increased data transmission speeds along with smaller denser data pipes lead to reduced signal integrity. In a nutshell; too much, too fast, and in too small of a space. But what exactly is happening to the signal itself that has it breaking down at high speeds?

Signal Integrity

A digital signal uses specific, measured, voltage changes to represent information. In a digital circuit, this voltage change is called a pulse. A pulse begins in the “off” state represented as 0. It increases to a specific voltage (“on” or 1) for a designated time (pulse width). The pulse then goes back to “off.” This series of on and off changes are specific for every piece of information in a digital system right down to the individual letters you are reading in this sentence.

Theoretically, an ideal pulse has precise, clearly delineated voltage changes. This makes the actual signal precise, hence making the digital signal, and the piece of information it represents, precise as well. Actual pulses do not work this way. Their voltages tend to increase gradually and can be distorted easily. If any individual pulse becomes distorted for any number of reasons (low voltage at high speed, crosstalk, impedance) the system might misrepresent the digital signal altogether. The end result will be a difference between the data send and the data received.

Regardless of some of the design concerns of backplane connectors, they are used almost everywhere. They can be found in computer servers, data storage systems, telecom infrastructures and more.