Mixed Signal and Microcontrollers Enable IoT
The Internet of Things (IoT) has become such a hot topic that many business and technical experts see it as a key enabler for the fourth industrial revolution – following the steam engine, the conveyor belt and the first phase of IT automation technology (McKinsey Report). Still, for all the hype, the IoT concept seems hard to define.
From a technical standpoint, the IoT refers to the information system that uses smart sensors and embedded systems that connect wired or wirelessly via Internet protocols. ARM defines IoT as, “a collection of smart, sensor-enabled physical objects, and the networks, servers and services that interact with them. It is a trend and not a single sector or market.” How do these interpretations relate to the real world?
“There are two ways in which the “things” in the IoT interact with the physical world around us,” explains Diya Soubra, CPU Product Manager for ARM’s Processor Division. “First they convert physical (analog) data into information and second they act in the physical world based on information. An example of the first way is a temperature sensor that reports temperature while an example of the second way is a door lock opens upon receiving a text message.”
For many in the chip design and embedded space, IoT seems like the latest iteration of the computer-communication convergence heralded from the last decade. But this time, a new element has been added to the mix, namely, sensor systems. This addition means that the role of analog and mixed signal system must now extend beyond RF and wireless devices to include smart sensors. This combination of analog mixed signal, RF-wireless and digital microcontrollers has increase the complexity and confusion among chip, board, package and end product semiconductor developers.
“Microcontrollers (MCUs) targeting IoT applications are becoming analog-intensive due to sensors, AD converters, RF, Power Management and other analog interfaces and modules that they integrate in addition to digital processor and memory,” says Mladen Nizic, Engineering Director for Mixed Signal Solutions at Cadence Design Systems. “Therefore, challenges and methodology are determined not by the processor, but by what is being integrated around it. This makes it difficult for digital designers to integrate such large amounts of analog. Often, analog or mixed-signal skills need to be in charge of SoC integration, or the digital and analog designer must work very closely to realize the system in silicon.”
The connected devices that make up the IoT must be able to communicate via the Internet. This means the addition of wired or wireless analog functionality to the sensors and devices. But a microcontroller is needed to convert the analog signal to digital and to run the Internet Protocol software stacks. This is why IoT requires a mix of digital (Internet) and analog (physical world) integration.
Just how difficult is it for designers – especially digital – to incorporate analog and mix signal functionality into their SoCs? Soubra puts it this way (see Figure 1): “In the market, these are two distinct disciplines. Analogue is much harder to design and has its set of custom tools. Digital is easier since it is simpler to design, and it has its own tools. In the past (prior to the emergence of IoT devices), Team A designed the digital part of the system while Team B designed the analog part separately. Then, these two distinct subsystems where combined and tested to see which one failed. Upon failure, both teams adjusted their designs and the process was repeated until the system worked as a whole. These different groups using different tools resulted in a lengthy, time consuming process.”
Contrast that approach with the current design cycle where the entire mixed signal designers (Teams A and B) work together from the start as one project using one tool and one team. All tool vendors have offerings to do this today. New tools allow viewing the digital and analog parts at various levels and allow mixed simulations. Every year, the tools become more sophisticated to handle ever more complex designs.
Simulation and IP
Today, all of the major chip- and board-level EDA and IP tool vendors have modeling and simulation tools that support mixed signal designs directly (see Figure 2).
Verification of the growing analog mixed-signal portion of SoCs is leading to better behavioral models, which abstract the analog upward to the register transfer level (RTL). This improvement provides a more consistent handoff between the analog and digital boundaries. Another improvement is the use of real number models (RNMs), which enable the discrete time transformations needed for pure digital solver simulation of analog mixed-signal verification. This approach enables faster simulation speeds for event-driven real-time models – a benefit over behavioral models like Verilog-A.
AMS simulations are also using assertion techniques to improve verification – especially in interface testing. Another important trend is the use of statistical analysis to handle both the analog nature of mixed signals and the increasing number of operational modes. (See, “Moore’s Cycle, Fifth Horseman, Mixed Signals, and IP Stress”).
For digital designers, there is a lot to learn in the integration of analog systems. However, the availability of ready-to-use analog IP does make it much easier than in the past. That’s one reason why the analog IP market has grown considerable in the last several years and will continue that trend. As reported earlier this year, the wireless chip market will be the leading growth segment for the semiconductor industry in 2013, predicts IHS iSuppli Semiconductor (“Semiconductor Growth Turns Wireless”).
The report states that original-equipment-manufacturer (OEM) spending on semiconductors for wireless applications will rise by 13.5% this year to reach a value of $69.6 billion – up from $62.3 billion in 2012.
The design and development of wireless and cellular chips – part of the IoT connectivity equation – reflects a continuing need for related semiconductor IP. All wireless devices and cell phones rely on RF and analog mixed-signal (AMS) integrated circuits to convert radio signals into digital data, which can be passed to a baseband processor for data processing. That’s why a “wireless” search on the Chipestimate.com website reveals list after list of IP companies providing MIPI controllers, ADCs, DACs, PHY and MAC cores, LNAs, PAs, mixers, PLLs, VCOs, audio/video codecs, Viterbi encoders/decoders, and more.
“Many traditional analog parts are adding more intelligence to the design and some of them use microcontrollers to do so,” observes Joseph Yiu, Embedded Technology Specialist at ARM. “One example is an SoC from Analog Device (ADuCM360) that contains a 24-bit data acquisition system with multichannel analog-to-digital converters (ADCs), an 32-bit ARM Cortex-M3 processor, and Flash/EE memory. Direct interfacing is provided to external sensors in both wired and battery-powered applications.”
But, as Soubra mentioned earlier, the second way in which the IoT interacts with the physical world is to act on information – in other words, through the use of digital-to-analog converters (DACs). An example of a chip that converts digital signals back to the physical analog world is SmartBond DA14580. This System-on-Chip (SoC) is used to connect keyboards, mice and remote controls wirelessly to tablets, laptops and smart TVs. It consists of Bluetooth subsystem, a 32 -bit ARM Cortex M0 microcontroller, antenna connection and GPIO interfaces.
In addition to tools that simulated both analog, mixed signal and digital designs, perhaps the next most critical challenge in IoT hardware and software development is the lack of standards.
“The industry needs to converge on the standard(s) on communications for IoT applications to enable information flow among different type of devices,” stressed Wang, software will be the key to the flourish of IoT applications, as demonstrated by ARM’s recent acquisition of Sensinode.” A Finnish software company, Sensinode builds a variation of the Internet Protocols (IP) designed for IoT device connection. Specifically, the company develops to the 6LoWPAN standard, a compression format for IPv6 that is designed for low-power, low-bandwidth wireless links.
If IoT devices are to receive widespread adoption by consumers, then security of the data collected and acted upon by these devices must be robust. (Security will be covered in future articles).
Analog and digital integration, interface and communication standards, and system-level security have always been challenges faced by leading edge designers. The only thing that changes is the increasing complexity of the designs. With the dawning of the IoT, that complexity will spread from every physical world sensor node to every cloud-based server receiving data from or transmitting to that node. Perhaps this complexity spreading will ultimately be the biggest challenge faced by today’s intrepid designers.
John Blyler is the Chief Content Officer for Extension Media, which publishes Chip Design and Embedded Intel® Solutions magazine, plus over 36 EECatalog Resource Catalogs in vertical market areas.