The Universal Serial Bus (USB) is the standard used to connect all sorts of devices today. But the universal in the name can be misleading at times as one would wonder why they have never made circular USB connectors.
Why don’t we have a circular USB port? Because it’s more space-efficient for mobile devices to have a semi-rectangular shape. When you have a circular shape with the same current-carrying capabilities for power, it will become far taller, and you will have a big raised area on our small or thin devices like cell phones.
The USB people also put into consideration the connector impedances and conductor lengths. The USB uses a differentia data signal that means tha you have matched inverted and non-inverted signals that are a great way to keep the noise down. This makes sure that any noise that hits both of the signals is eliminated.
Circular connectors also have more wrong positions to be rotated that might fit into the connector if you can t see the connection. The circular connectors can be forced into the mate in the wrong position. But when you have a flat connector, there are only two ways that you can insert it, and the current connector has a much stronger keying mechanism.
But for differential coupling to work, the signals must be pretty close to exactly the same length over the same path. That is impossible to achieve with an axial circular connector like a phone plug. It is also much more difficult to keep all the signals impedance matched over these plugs.
They are used mainly for casual audio, which is a very slow speed signal, but even professional audio cables for sensitive things like microphones use parallel pin connectors and impedance controlled differential signaling.
USB has the advantage of remaining pretty compatible for many years given the right choice of the target end cable; extending a circular connector with additional signal pins would have been problematic.
USB 1 and USB 2 only had four conductors; by that time, it was feasible to put them into a circular plug though it has some disadvantages as the connector can rotate. USB 3 had eight connectors, and the USB –C has more than 16 connectors. This would become extremely difficult or impossible to put on a circular connector.
One of the USB conductors carries power for powering simple devices like keyboards and memory sticks. It is generally not a good idea to have uncovered power connectors, while the amount of power that is supplied is of no risk to humans or of fire, but if it contacted other electronics, it could destroy them.
But when you have a straight line insertion, it makes it easy to make some of the connectors longer and get a safe sequence of connections. On a circular connector, all of the signals connect at the same time after having some false connections before, and the longer the wiping action is better at getting good contact.
When you have a circular plug, it must, by design, penetrate deeper inside the device and taking up more space. Well, that is not a problem with a simple thing like a speaker, but let’s say for a modern phone, there is not enough space. This could end up taking space from the battery and thus giving a shorter battery life and which is not a tradeoff as most users would want.
Inside The Pen Drive
The rectangular shape doesn’t increase the width unnecessarily, and it is also easy to fit onto a device that is already rectangular. Since there are also multiple pins on a USB port that should connect with the matching pins on the other side, the rectangular design makes it easier to enforce.
If we cannot adhere to the standard, we cannot call it USB. The connector was chosen by the standards committee and is cheap, relatively impact, and also not easily confused with the other connectors. In fact, one of the advantages of the USB is that it is easy to recognize virtually from all other connectors.
The USB standard organization agrees on the size and the shape, and if you want to conform to the standard, you have to use one of their recommendations. If you don’t, then legally, you are not supposed to sell it as a USB device. However, almost any connector will do the job. There is nothing that is special about the standard USB connectors. They were specified with cheapness and ruggedness in mind and not the electrical quality.
Why Are USB Ports Rectangular and Not Triangular?
The maker of USB addressed this issue and said that USB ports needed to work with blind insertion like behind a PC. Some of the ports that were replaced were round PS.2, and they were hard to line up blindly. The rectangular shape solved this problem with only two ways to orients and only one that fit.
A triangle would have three ways to fit, and only one of them that worked. This would not be an improvement.
The most important question is, why did it matter the way that you turned it? Why not allow the connector to connect either way? The problem here came with a cost. Though this problem has been solved with the reversible USB-C connector, this requires additional electronics that were not economically feasible at the genesis of the USB connector.
The other reason is that triangles not only have three sides, but they also have three points, and any place that two faces met at an acute angle point, you get an inherently weak point that is easily damaged by sheering and crushing. So you get a connector that has three weak and vulnerable points.
The spaces where the faces meet also is very small, and this reduces the effective space within which you can place internal components or wires.
Why The USB Plug So Stupidly Designed
Every time you see a design that is dumb, you can always conclude that the main factor was the cost. When USB came in the mid-1990s, they sought to replace a panoply on a PC; serial-parallel, keyboard, game, mouse, and others.
All these ports were direction-dependent, so the extra cost to make a direction-dependent plug was not a big priority as driving down the cost to foster adoption. Making a connector that would be reversible would have increased the manufacturing costs and complexity.
The primary use case at the time was also to connect and leave connected like a wired keyboard, printer, mouse, game controller, or scanner. The ease of connection was a relatively low priority since that would be a relatively rare event. The popularity of portable music, smartphones, and portable mass storage came about after the USB specification was first envisioned.
Drawing from the significant advances that have occurred in technology since the 90s, the USB Type-C connector is available to fix that design deficiency once and for all by introducing an insensitive orientation connector.
Conclusion
We should note that the reversibility of the USB-C connector came at a significant hardware cost in the endpoint. In order to allow the connector to go neither way round, then there should be electronics that switch over the signals inside of the device.
Since the signals are running at 10GHz, this is not trivial. There must have been a considerable argument between the engineers wanting the economy and simplicity of the manufacturer and marketing.
