Ara Knaian, the chief mechanic engineer at Project Ara, told about Ara platform engineering efforts, the endo, and how the modules connect to endo.
The Spiral 2 prototype
The Spiral 2 prototype phone was presented on the slide. The Spiral 2 consists of endoskeleton and the modules that slide into endoskeleton on the front and back. The endo has a spine that runs vertically. That’s a strip of metal devided in two halves. The ribs separate the module slots.
What is Spiral 2 Endoskeleton
Endo is the element of the modular phone that ties all the modules together into a single unified device. One very important function of the endo is providing the phone with mechanical strength, so when you sit on the phone, it has enough mechanical strength so the glass doesn’t brake, for example. The endo is responsible for module retention with help of electropermanent magnets (EPM).
The endo implements the on-device network. So there is the data switch, called UniPro switch, which is analogous to the ethernet switch. UniPro switch allows any module to communicate with any other module at the speed of up to 20 gigabits per second.
There is a RF bus in the endo, so the endo allows the antenna signals to be routed from module to module.
The endo is responsible for the power management and distribution.
How the Spiral 2 Endo works and what it does
Electropermanent magnets are used to hold the modules in the endo. Electropermanent magnet has the best features of both electric and permanent magnets. Short pulse of current in positive or negative direction will turn the magnet on or off. But after that the magnet does not use any power to stay in a new stage.
In Spiral 1 EPM was implemented into the module, but in Spiral 2 the EPMs are in the endoskeleton.
Electrical interconnections between the module and the endo are implemented in Spiral 2 with spring pins. There are black areas with the pins on the endo which are called “interface blocks”. All electrical connections between module and the endo take place over those pins.
Each interface block has 12 pins. 8 of them are devoted to M-PHY serial data connection. The other 4 pins remain the data bus (power and ground pin for the DC power bus, RF pin for the antenna bus, wake/detect pin which is used for power management).
MIPI M-PHY is used for the data connection between modules. Two lanes in each direction: two lanes from the endo to the module, and two lanes from the module to the endo. Data goes simultaneously in both directions. The range of available speeds is very large (from 2.4 Mb/s up to 9330 Mb/s).
Electrical connectors are one of the most unreliable parts of any electronic device. So the contactless media converter is being developed. This is the way of sending data through the air from one module to another through very small air gap of about 0.15 millimeters. Toshiba confirmed that they had done successful high-speed communication over the air gap using inductive pad design. Toshiba also designed bridges and switches, which will enable modules easily communicate over the UniPro network.
Possible look of the endo in Spiral 3 design was presented. It is subject to change. But it shows inductive pads on the interface blocks for data communication.
RF bus and power bus were briefly described as well.