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Sensors and sensor applications are proliferating, thanks to technology miniaturization, low component costs, pervasive connectivity, and the design community’s imaginative and often visionary use of them in mobile and mobile-influenced products. Sensors are now key in enabling technologies in all types of products, from smartphones to biometric skin patches, industrial machinery, and automobiles. They are providing impetus for the Internet of Things (IoT), creating “one of the most significant opportunities for the semiconductor industry since the Internet boom,” according to PwC.

Despite the success and increasing promise of these markets, sensor integration has been particularly vexing for designers. Traditional integration technologies are usually sensor-specific, requiring designers to use multiple interfaces, such as I2C and SPI, when deploying numerous sensors in a device. This fragmentation increases pin count, which consumes precious board space while impacting product development time and integration costs. Designers also struggle to achieve application performance requirements on low-power operation, which limits sensor use cases and scalability in small, battery-operated devices. 

Fortunately, a new core sensor integration standard (a forthcoming interface) alleviates these issues to support the growing use of sensors in embedded systems. The new interface, MIPI I3C, unifies traditional interfaces to standardize the fragmented industry while providing a scalable technique that is compatible with key I2C specs. MIPI I3C drastically reduces pin count and supports low-power, high-performance operating requirements. It is a game-changing interface that should streamline sensor integration and drive cost efficiencies.

MIPI I3C also provides substantial data throughput and energy savings to meet a variety of design needs. On a standard CMOS I/O, MIPI I3C can be used in a single data rate mode (SDR) to support a base clock of 12.5 MHz. It also provides an optional higher performance, high-data rate (HDR) mode that can double and even triple data speeds while dramatically improving power efficiency. When used in HDR mode, MIPI I3C uses one-eighth the power of I2C, for example, while providing 100 times the bandwidth (see figure 1).

Figure 1: Comparing energy consumption and peak data rates for I2C and MIPI I3C.

Smartphone Sensor Integration

Smartphone manufacturers want to add new sensors and sensing technologies to their designs to improve user experiences and offer advanced features, such as pedestrian navigation or virtual reality. Sensor fusion is employed to aggregate and analyze data from multiple sensors to support complex functions, such as differentiating between walking and driving or controlling power-consuming backlighting or Wi-Fi functionality when a device is in idle mode.

Sensor integration in smartphones has been especially challenging because high-end devices can have 10 or more sensors and possibly require 20 out-of-band control signal lines. The interfaces must provide always-on features so sensors like pedometers can gather and share data, even if the device is in idle mode, without adversely impacting battery life.

I2C and SPI can both interface multiple sensors, but the approaches require out-of-band control signals to implement interrupt functionality, which increases pin count. Additionally, I2C is not practical for quickly sending large amounts of batched data needed for many smartphone applications, and SPI has a high pin count and requires a dedicated chip select pin for each sensor. 

MIPI I3C can replace both options with a two-wire interface. The specification accommodates multiple sensors on the same communication bus and eliminates the need for additional I/O pins by using in-band methods to issue interrupts or initiate sleep mode. MIPI I3C also promotes always-on sensing at very low power, and it enables sensors to batch data and transmit it quickly to minimize energy consumption to help preserve system battery life. Additionally, MIPI I3C provides synchronous and asynchronous time stamping modes to improve the accuracy of sensor-based applications over time and allow individual sensors, such as gyros and accelerometers, to work better together.

The result is a more flexible and simpler implementation that can be applied to interconnect numerous classifications of sensors. Table 1 presents a sampling of sensors and functions that can be integrated in a smartphone or other device with MIPI I3C.

Table 1: Partial list of sensors and related functions supported by MIPI I3C.

Integrating Sensors in Wearables with MIPI I3C

MIPI I3C is useful for many applications beyond smartphones. The wearables segment of the IoT is another exciting case study because the category covers a range of products—from fitness bands to smart watches, smart clothing, medical devices, virtual reality head-mounted displays, and others—that can require a broad range of features and functionalities.

Traditionally, designers have relied on I2C to integrate sensors in wearables, but the industry has needed a more power-efficient interface that can be used for various types of implementations. Product development for wearables is also challenging because a device might require one or more sensors, but there may not be room to accommodate the component(s), traces, and battery in very limited physical space.

Performance requirements vary depending on the device and applications, but wearables often operate on coin-cell or other small batteries for extended time periods—months in some cases—and therefore the device must function on very low power.

As in smartphone implementations, MIPI I3C can connect and manage multiple sensors in a wearable device. It can replace the out-of-band digital control signals with in-band interrupts to minimize wiring requirements, save real estate on a printed circuit board, and help reduce costs. Because the new specification dramatically improves power performance while delivering an order of magnitude improvement in data speed compared to I2C, designers can meet key functional requirements for current designs while bolstering device performance as the wearables industry continues to advance.

Game Changer for Integrated Sensor Systems

MIPI I3C provides significant integration and operational advantages. This article highlights its applicability and benefits for smartphones and wearables, but the specification is also ideal for sensor integration in many other mobile and mobile-influenced applications, from tablets to IoT applications like smart homes, connected appliances, and cars.

MIPI I3C can be adopted conveniently and without risk. It allows most types of I2C devices to coexist with I3C devices on the same bus, enabling vendors to migrate current I2C designs to the new standard and newly designed MIPI I3C devices to work on existing legacy I2C buses. MIPI I3C is a future-looking standard that should find broad market acceptance. It standardizes a fragmented industry to help companies meet the increasing demand for innovative, sensor-enriched products under very rigorous business, market, and design conditions.  

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