After the USB Type C connector was released, I thought it would be a good thing. And it is. It has so many improvements, it’s hard to to complain. Okay, lets be real, I can complain about anything. Try me. I practice a lot.
Let’s go over some of the good things that people generally like & use. We have a reversible connector, which simplifies plugging things in. Then there is alternate video modes, allowing DisplayPort to use the same connector. And, no more A & B side, so reversible cables too.
Higher power which can eventually allow us to eliminate more of the specialized power bricks and wall worts that we currently use. We can have universal power supplies with multiple USB Type C connectors, that can power, or charge, lots of different devices.
The increase in speed helps too. Even if we can’t get 100% saturation of the channel, (assuming both ends could do it), we still get pretty impressive throughput.
Now on to the down sides, (everything must have one or more!).
First up, the connector is actually larger than the Micro USB Type B we commonly refer to as Micro USB. While USB Type C has more functionality, their are times when all this extra functionality is not needed.
Power delivery is problematic at times. Seems that their is a serious difference between what the USB C connector can supply by default. And what a device can negotiate. Some of this makes sense. We don’t want to supply 20 volts at 5 amps by default…
The naming of the speed and configuration is so off the wall, it’s practically guess work to know what is possible. Or what a connected device is using. The complexity of speed verses how many channels, 1 x 5Gbps, 2 x 5Gbps, 1 x 10Gbps, and 2 x 10Gbps all add to the confusion. USB standard version 4 complicates maters even more.
Then their are the alternate modes. All the alternate modes complicate things. Some later alternate modes should have been declined. DisplayPort was the first for video and ended up being a bit of a standard. Then along comes HDMI wanting the same treatment. Except now we get devices that don’t clearly define if they are Alternate mode DisplayPort, with HDMI connector. Or Alternate mode HDMI with HDMI connector. Which are NOT the same thing, and generally WON’T work the same.
So I propose a new, smaller, connector. Yet another USB connector you say?
Yes. One even smaller than Micro USB Type B. Sure, it can’t pack as much functionality as the current Type C into a more limited size & pin count. But, it will perform much of the same purpose, simplifying some designs.
As for what could use the small connector, that’s easy:
- Some wireless headsets
- Wireless ear buds
- Some thin phones
- Smart watches
- GPS dongles
- USB headphones
- USB headsets
- potentially maintenance ports of misc. devices
- etc…
What does a small device need?
- Smaller foot print than existing USB Type C connector, which is 8.25mm wide. In fact, should be smaller than the existing Micro USB Type B at 6.8mm
- Power, definitely more than Micro USB Type B can supply
- Perhaps a water proof solution, for both cable and receptacle
- Even a magnetic connector option
- Of course, reversible connector & reversible cable, (if Micro-C to Micro-C is needed)
- Continue to put the “spring” in the contacts on the cable side
- For data:
- Modern, reasonable speed, >=20Gbps per lane
- Current encoding, (like 128b/132b for 20Gbps)
- potentially full duplex
- Some alternate modes
- DisplayPort
- Perhaps some asymmetric modes to improve speed in one direction
- Perhaps some additional half duplex speeds, like 1Gbps & 2.5Gbps. These would be for simplified uses.
Here is a proposed configuration:
- 2 x positive power
- 2 x negative power
- 3 pairs of data
All in all, just 10 pins. Much less than the 24 pins used on the USB Type C connector.
Here is a proposed connector layout:
A1 A2 A3 A4 A5
GND TX+ HX+ RX+ VBUS
-------------------------
VBUS RX- HX- TX- GND
B5 B4 B3 B2 B1
Description:
Positive and ground have 2 pins & wires each to allow reasonable amount of power to be supplied. With this design, they are automatically reversible. If needed, these pins can be wider, though the ground should connect first.
The main 2 pairs make up a single full duplex, 5, 10 or 20Gbps USB channel. Or alternatively, a PCIe lane / Thunderbolt.
The 2 center pins, A3 & B3 are re-assignable. For example, they could be potentially assigned as a half duplex, USB 2 type 480Mbps channel for connections that don’t need more. Auto detection could be based on lack of voltage on the main transmit pair.
This is basically a USB 3 Type A connector signal setup. But, we allow higher, negotiated voltage and power. Not to mention alternate modes for the A3/B3 pair. So a USB Type A to USB Type Micro C cable is possible, with full functionality on the host side, if the host side supports it.
The normal operation would be a cable with USB Type C on the host, and USB Type Micro C on the device. This should be part of a later USB standard.
For size, the normal Type C connector is 8.25mm wide. Based on quick math, we could in theory get down to 3.4mm. But, that is likely not achievable. Or practical. Perhaps 5mm is a more reasonable goal. But we should target smaller than the Micro B at 6.8mm.
Now for some alternative modes. None would be required:
Assign A3/B3 as USB half duplex
There are times a simplified communication channel is needed. The old, single pair, USB 1/2 half duplex is suitable. By default, nothing would be assigned.
However, if the remote transmit lines don’t have any signal, then we would assign USB half duplex to this pair.
Further negotiation can be done to change the A3/B3 function as desired.
Higher speed on A3/B3
Sometimes when simple half duplex channel is acceptable, but perhaps higher speed would be helpful.
These 2 new speeds could be added:
These should probably use modern encoding of 128b/132b. And perhaps allow 5, 10 & 20Gbps too. After all, these speeds are already part of the standard.
Asymmetrical full duplex:
Their are times when communications is heavy in one direction and not the other. For example, during backup to an external storage device we send lots of data to the device, but really only receive command results back. So, if we can assign the A3/B3 signal pair to be a second channel in the heavier direction, we can double the speed in the important direction.
This would apply to 5, 10 & 20Gbps speeds equally.
DisplayPort:
As the prior USB C, & version 3 & 4 allow, we should support DisplayPort over USB Type Micro C. Their would be limitations;
- 3 lane Display Port; no USB
- 2 lane Display Port; 1 pair for USB, half-duplex
- 1 lane Display Port; 2 pair for USB, full duplex
But, with higher speed lanes, this is less of a problem.
Thunderbolt:
This would allow sharing the 3 pairs with USB, DisplayPort & PCIe. Priority may end up with DisplayPort as the most visible one.
Alternate modes for A3/B3:
Their are some odd devices that may want to use a standard cable. Possibly for power. So, we allow A3/B3 to be re-assigned for that use. Meaning by default, a device would leave it’s A3/B3 line in a floating state. And a host that supports this function, would also not use the lines unless told to do so.
Their probably needs to be current & voltage protection on the lines. On both the host and device side.
One possible use could be analog audio. With 2 lines, we can send stereo out, and use the normal ground pins as signal returns. The specialized cable in this case would only have 4 wires, A3 shielded in A1 GND. And B3 shielded in B1 GND.
In the case of a headset, we may have to have the transmit lines become the microphone. Perhaps even suggest the microphone to have a built in ADC so that the low power analog signal won’t be noisy.
And if power is needed, for an external amplifier, it’s available too. But, negotiation is required over the full-duplex pair.
To be clear, it’s almost certain today that digital earphones, headsets and digital connections to amplifiers is more practical. And would likely be cheaper.
Let’s review.
Would it be better to have 4 pair of signals?
Instead of the proposed 3 pair?
Do we want any line, or lines, as some kind of aux channel?
Most cables probably can support 20 volts without problem.
But, do we want to limit the current to 3 amps instead of 5 amps?
So that the cable can be both smaller and more flexible?
Or even support 2 cable types, 3 amp & 5 amp?
What do you think?
Wanted?
Needed?
Required?
Or completely, utterly useless?
Arwen Evenstar's blog 
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