Everybody loves wireless: It's the main impetus driving technology innovation and social and business communications today, and it will continue to drive innovation for years to come. Yet an under-appreciated reality is that wireless is very dependent on wired connections. In fact, wireless is only as good as the wires that support it.
In a device like a smartphone, for example, a full ecosystem of internal wiring standards interconnects a couple dozen components, from the modem and application processor to the microphone, speaker, sensors and other peripherals. In this article I'll describe these wired connections and the interfaces and architectures that are used to build mobile and mobile-influenced devices. I'll also point out some key challenges engineers face when doing this work.
Engineers today are highly motivated to design mobile and mobile-influenced products. Deployments in these categories are increasing at staggering rates. IDC projects worldwide smartphone shipments to reach 1.87 billion by 2018. When you add in mobile-influenced devices spurred by the Internet of Things and M2M services, the number of smart devices goes up exponentially. Semico Research projects that the number of intelligent connected devices will reach an installed base of 36 billion units by 2020.
A Quick Lesson in Wired Interfaces
The interfaces used to connect the components in devices can be considered "inbound" or "outbound."
Inbound Interfaces: For incoming communications, wireless signals enter the RF front-end antenna and receiver, and a wired interface carries the signals to the modem. The speed of this interface can easily exceed several Gbps for higher-speed modems. Another interface moves modem signals to the application (apps) processor, where the signal is executed upon and/or moved elsewhere. (Of course, the reverse operation occurs when wireless transmissions exit the device.) Different modem types support varying over-the-air speeds: from 300 Mbps for WLANs and 100 Mbps for 4G LTE, down to 1 Mbps for Bluetooth and even less for IoT modems that use Zigbee.
Cameras, microphones, and touch sensors also employ inbound interfaces. The interface connecting the imaging sensor to the apps processor must support high-resolution cameras offering 20 MP at 30 or 60 FPS and operate at 10 Gbps and higher rates.
Another example: an audio interface exchanges audio/voice packets and messaging among microphones, Bluetooth, the apps processor, and speaker. A touch interface interprets finger presses on the display and sends raw or processed data to the apps processor.
Outbound Interfaces: There are numerous outbound interfaces, but the primary one connects the apps processor to the internal display. In some cases, it can interface to an external device such as a TV. In uncompressed data scenarios, 4K displays can require data rates in the multi-Gbps range, but compression of 2:1 or 3:1 can reduce these rates. Often the rates are limited if the interfaces must carry signals directly on the product's glass display.
Design Challenges Abound
The industry is always concerned about reducing the number of wires used in devices, while improving performance, mitigating electromagnetic interference (EMI) and minimizing power consumption. Here's why:
- The number of wires matters because each pin on a chip raises the chip cost and each trace on a PCB raises the board cost. With the exception of some types of memory chips, parallel interfaces have largely been replaced with serial interfaces that reduce wires and therefore cost.
- Performance demands continually increase, and thus higher-speed modems are used for connectivity, higher-resolution displays, and cameras. Higher-performance interfaces are also needed for memory and storage to help improve overall device utility.
- Faster interfaces can increase EMI, which can compromise performance. Interfaces must be carefully selected and applied to control EMI as much as possible.
- Faster also generally means more power. Interfaces that minimize active power are required to help save battery life, which is precious in small devices. Depending on the use case, interfaces can also be applied to minimize power consumed when the interface is not active.
Employ Wires Strategically for Strong Designs
Engineers from companies around the globe are aware of the power of the smartphone and its influence on multiple technologies and industries. When pursuing this work, engineers must develop the wired interfaces for their components quickly to be early to market with their innovative designs. They should keep in mind that success in wireless ultimately comes down to the wires inside the device and the interface specifications that interconnect the components. They should use interfaces that meet the specific performance goals for their components and end products—a complex endeavor, without a doubt.
Ultimately, wireless device connectivity would be hamstrung without wired interfaces. Engineers who employ interfaces that most appropriately meet their specific needs and anticipate future markets will have strong designs and a better chance of success.
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