Posted by Eric Huang on June 28, 2019
The USB-IF anticipated that process nodes would advance to a point where the USB 2.0 standard of 3.3V signally wouldn’t work anymore. Or rather, the IO voltages in advanced process nodes don’t support generating or receiving 3.3V for signaling.
At the same time, the expectation is that USB will continue to be integrated as the primary external interface for peripherals and data. This means that PCs, tablets, phones, set top boxes, and TVs will have USB alongside WiFi and Bluetooth.
Since newer nodes have IO voltages that can’t support 3.3V signaling, for USB 2.0 interoperability, the 3.3V signaling must be provided outside the system-on-chip (SoC).
The expectation is that initially there will eUSB2 chips that will bridge from an SoC with low voltages (Figure 1). This will be an eUSB2 repeater. Then users who are using a standard USB mouse from 1998 or a 4MB flash drive from 2005 can use it with an advanced laptop of 2023. This sort of setup will work because eUSB2 IP will boost the signal and provide the support for external peripherals or legacy peripherals.
Figure 1: eUSB2 block diagram
Since eUSB2 uses lower voltages, taking advance of the lower voltage reduces the power consumption in a design.
Laptop PCs and tablets can make use of this. The eUSB2 1V can be used between chips. No repeater is needed as long as the USB peripherals have eUSB2 IP.
The eUSB2 can be used to interface to a touchscreen, a pointer stick, or a touchpad. It could be interfaced to anything inside a product shell/chassis at up the 480 Mbps or Hi-Speed USB 2.0 rates.
eUSB2 uses lower voltages and power.
Features like single ended signaling instead of a differential pair signaling lowers power even further.
This reduces the power consumed by a full order of magnitude from 10s of mW to single mW for Active or Idle. This means that when actively transmitting it uses less power.
It also means when Idle and “listening” for data (like touch screen presses or keyboard clicks or mouse clicks) it uses less power.
The eUSB2 implementation is required for all USB speeds since all USB 2.0 speeds are required for interoperability. USB 2.0 includes Hi-Speed (480 Mbps), Full Speed (12 Mbps), and Low Speed (1.5 Mbps).
Here’s a fancy video with Morten (who briefed me on specific technical things) and Gervais (my boss).