IoT Design Tips and Methodologies

Key Takeaways

• Learn about different IoT fields and applications
• Learn the basic building blocks for IoT design
• Mixed signal, wireless, and low power tips for IoT design

The Internet of Things is a network of billions of devices that collect, process, and provide information to improve our quality of life. As a rapidly growing field, IoT devices now include personal wearables, industrial machinery, medical devices, and more. A single IoT device merges technologies such as RF communication, mixed-signal capabilities, and high-speed data transfer, all while minimizing power consumption. For this reason, a lot goes into IoT design to ensure reliable and efficient devices.

We’ll be taking a detailed look into different elements of IoT design–the basic building blocks of IoT devices, IoT design standards, low power design, mixed-signal design, and how to incorporate SPICE into your design flow.

IoT Applications

IoT devices are used in multiple industries, from consumer electronics to medical devices. One such application is with RFID (radio field identification). With RFID, businesses have been able to track the location of items equipped with RFID tags. This allows them to implement systems with higher efficiency tracking and increased information. Below are a few other industries where elements of IoT are playing an ever-increasing role.

Business

IoT can improve areas of business such as:

• Automated office environments, customer service, and resource management.
• More data on products, services, and interactions.
• Logistics for inventory management, tracking, and maintenance.
• Customer-facing products that send a notification when they need repair.
• Retail efficiency like the nest thermostat and smart light bulbs. 

Manufacturing

In industry and manufacturing, plants, mills, and refineries have all become safer work environments through the use of smart vests, smart helmets, glasses, and other equipment that collect health, location, environment, and productivity data. These devices connect together and provide information during plant operation that, combined with online analytics, ensure the safety of workers and the smooth operation of plant machinery.

Athletics and Healthcare

The benefits of IoT are not just felt by businesses – IoT has also transformed athletics. Both amateurs and professionals are able to wear wristband sensors that measure vitals like heart rate, body temperature, and more. This provides individuals with more detailed information as to their performance and response to stimuli.

Health-related products that monitor essential bodily statistics have also transformed the healthcare and biotech industries. Devices like smart inhalers that track usage or ingestible sensors that dissolve in the stomach can communicate outside the body and increase the amount of data healthcare providers have access to, resulting in better-informed decisions.

IoT Design: Basic Building Blocks

At its core, an IoT device has a couple of key components that define it: sensors, a wireless connectivity block, and a power management block. The main challenge in successful IoT design is having them all work together smoothly.

Sensors

Firstly, sensors focus on gathering data from the outside world. Examples include sensors that measure temperature, pressure, humidity, infrared, cameras, and RFID tags. When designing your IoT device, think not only about what real-world information the device itself could benefit from, but also keep in mind it will be communicating to other servers, devices, and nodes as well. Consult this blog post to hear our tips on selecting sensors, including design considerations and specific applications.

Wireless Connectivity Module

Secondly, the wireless connectivity module plays a crucial role in connecting to the world beyond the device. Common communication modalities include Bluetooth, Zigbee, WiFi, and NFC. For direct internet access, consider using GSM/ LTE or WiFi. Each of these modalities have different times when they’re connected, different ranges, and different power consumptions. For example, some NFC devices can be wireless powered to communicate with a transceiver, while WiFi-enabled devices will need always-on power.

Power Regulation Module

Finally, your power regulation module is key in your device's portability and communication abilities. If you’ll be powering your device from a battery, designing with power efficiency in mind is crucial. To keep your device running as long as possible, use voltage regulators with low quiescent current. Consider designing your circuit so that only relevant sub-circuits are powered at any given time.

IoT Design Essentials

The real measure of success for IoT design is to pack these previously discussed technologies into a single compact device. This device should be cost-effective and might even need additional capabilities for digital signal processing, natural user interface processing, control operations, or analog sensing.

There is a constant push to make IoT devices with improved performance, power efficiency, higher range, and reduced size. A device may contain a CPU, memory, graphics, processing, and wireless circuitry. In order to create the smallest device possible, many of these elements can be put onto a single system on chip (SoC)–but not all.

Due to the need for space-saving, the critical difference for IoT design is having the entire product or board designed as a single unit, as opposed to many smaller individual boards like in the past. This will require working closely with mechanical designers to ensure that signal integrity, thermal management, and size are all accounted for.

When designing IoT, keep in mind that sensors and ICs are rapidly evolving. The chips used on a product might become out-of-date faster than you think. For this reason, compartmentalize the design with sub-circuits, which allows for a systematic approach and makes updating parts on the circuit easier. Consider each sub-circuit input and output and how they integrate into the larger device as a whole.

Important Standards for IoT Design

IoT architecture can be described as three different layers:

1. Devices layer with sensors and actuators that gather data.
2. Edge layer with data processing components that filter, aggregate, and do preprocessing.
3. Cloud layer that connects with mobile apps or web-based apps that do the final processing.

Devices don’t exist in a vacuum, especially in IoT. They will have to function, communicate, and integrate with other systems. When designing an IoT device, consider how it fits into the overall architecture. The best way to do this is by adopting and maintaining standards. Consider adopting a single standard, such as IEEE 243, and applying it as you create your device. For the longevity of your design, look beyond basic functionality and consider the context it will be used in and, especially important, what other devices it will be communicating with.

For even more standards, consider looking into those from the Institute for Printed Circuits (IPC) as a starting point. Other standards-based IP solutions include:

• Interfaces: MIPI DSI, CSI, SLIMbus, UniPro, DigRF, BIG, D-PHY, M-PHY, M-PCIe, USB, HDMI, SDIO
• Memory: SD/eMMC, NAND, LPDDR, Wide IO
• Analog IP: AFE, A/D (sensors, radios), power monitors, thermal sensors
• Systems/Peripheral IP: microprocessors, bus and audio IP, and timer IP

Low Power IoT Device Design

Because your IoT design will likely be mobile, designing it to consume the least amount of power is crucial. As opposed to making your device always-on, include different operating modes. Additionally, having smart power management will increase the runtime of your device. For mobile devices, you’ll either need to use an energy-harvesting circuit (oftentimes utilizing inductive wireless power transfer) or rely on battery power.

Battery Power

One of the best ways to conserve battery power is to turn off portions of your device when not in use. To do this, divide the PCB into functional blocks, and for each block, allocate an appropriate power consumption budget. Choose power regulating ICs that meet your specs and ensure that each block of your design stays within its allocated budget.

Memory

The memory module of your IoT device will also consume power–choosing the right memory is important in staying within the power budget. For example, in using direct memory access (DMA), you’ll have better power savings but lose some latency and throughput compared to dynamic random access memory (DRAM).

Precise Power Budget Calculations

Avoid energy wastage from long PCB traces or numerous vias. Going from one plane to another can contribute to unnecessary losses on your board. Precise power budget calculations and efficient power delivery networks will increase the longevity of your device. Use a precise power network analysis tool to get an accurate picture of your device's efficiency before manufacturing and testing.

Wireless Design for IoT

Your device will be connected to the rest of the world wirelessly, likely through WiFi, Bluetooth, or some of the other previously mentioned modalities. Therefore, it’s important to familiarize yourself with various wireless network protocols.

Keep in mind that governments regulate the usage of the radio frequency spectrum, and certain frequency bands are allocated for specific purposes. WiFi operates most commonly at the 2.4 GHz frequency, NFC at 13.56 MHz, and other RF protocols at their own frequency. For this reason, utilizing an off-the-shelf wireless module that already meets government and industry regulations can be purchased and incorporated into your design.

Antenna design is also another crucial aspect–when designing your PCB, consider the orientation, gain, and directivity of your antenna, then select an antenna that matches the desired form factor. The Z-Wave mesh network topology can support hundreds of devices; for example, Sigfox uses the new ultra-narrow band (UNB) for radio message exchange.

Noise

Your device will be operating among all the other devices using their own wireless communication standards. For this reason, noise can become a larger factor. Devices will spend most of their time in idle or standby modes and only briefly turn communications on for transmission and reception for short bursts. Familiarize yourself with methods of dealing with RF EMI and incorporate them into your design.

Temperature

Temperature can also have a significant effect on communication as well. Consider the temperate ranges you’d like your device to operate in and ensure your components all meet these specifications.

Mixed Signal Design

Your IoT device will collect data from the real world through analog sensors that need to be converted to digital signals. Once in a digital format, data can be encoded and manipulated and even sent out wirelessly.

You will need to have a processor capable of moving data at high speeds. For this reason, you will need to design your layout to deal with issues such as crosstalk, clock skew, propagation delay, attenuation, and impedance matching. As is good practice with mixed-signal layout, separate your analog and high-speed digital sections into different parts of the board.

Compact Design

Fitting all of the various sub-circuits and modules into a single, compact PCB will require working with more advanced design technologies. These include high-density interconnects (HDI), embedded components, and other compact components such as multi-chip modules (MCM) or three-dimensional ICs (3D-ICs). Make your board even more compact with multilayer PCBs.

Ensure that the form factor of the PCB is set and agreed on. Specifically, talk with the mechanical engineer and product designer to ensure that the manufacturer has the capability to assemble and produce your design. Component placement becomes even more critical, as specific parts of the PCB may be susceptible to mechanical flexes. This is where a flex design might come in handy.

Flex Design

You may also have mechanical limitations in your design, which might be able to be solved with flex or rigid-flex boards, an ever-increasing popular alternative to standard rigid PCBs. Specifically, instead of having a standard rigid PCB that connects to a sensor with a complex wiring harness or high-density interconnects (HDIs), the PCB components, interconnects, and sensors can be placed on the flex PCB. This reduces the amount of interconnects and wires, which helps miniaturize your device.

SPICE Simulations

Utilizing a SPICE tool during your design and production process will allow you to regulate your design’s power and usability. As with most consumer electronics, designing for manufacturability and product yield is crucial in creating successful boards.

With SPICE simulations, you'll be able to get your tolerances set based on manufacturing yields and reliability standards. SPICE simulation can also help you keep track of power efficiencies and design vulnerabilities as well as analyze for impedance and determine form factor limitations. SPICE libraries will also have easy-to-access component parameter integration and modeling, with templates to build custom models.

Cadence’s PSpice program gives you access to over 33,000 components, making it easy to ensure component yield and reliability, validate electrical performance, and further optimize your design before production.