Connectivity chipset or module for IoT systems: solving the dilemma

According to Stastita, by 2025 IoT devices are expected to number more than 75 billion, far outnumbering the UN’s forecast of 8.1 billion people on Earth by that year. IoT is probably one of the biggest drivers for technology companies. Probably the most important feature of an IoT device is that it is connected.

Wireless connected devices have an RF radio, antenna and associated circuit to convert electrical signals in electromagnetic waves and vice versa. Designers have two options to implement this circuit: a) use RF chipset and design associated RF section and b) use a module with RF chipset and associated RF section already mounted. In this article we will compare both approaches and help designers to make an informed decision.

RF section using chipset and module

Implementation of an RF section using the chipset approach consists of an RF IC, antenna, balun and filters, matching networks, crystals and other passive elements. Figure 1 is the reference schematic of the implementation using STMicroelectronics’ BlueNRG BLE SoCs.

Figure 1: BlueNRG-2 reference schematic. For a clearer image, click here.

Implementation using the module approach is much simpler. The same circuit as in Figure 1 can also be implemented using a readily available module. Figure 2 is the pinout and internal block diagram of BlueNRG-M2SA module from STMicroelectronics. The module is implemented using BlueNRG-2 SoC and associated circuit.

Figure 2: BlueNRG-M2SA pinout and internal blocks. For a clearer image, click here.

Comparison between chipset and module approach

There are three main aspects to be considered while selecting a right approach: a) time to market, b) certification and c) cost. We will review each of these aspects to arrive at a logical understanding.

Time to market

Some steps to design an RF section using a chipset are as follows:

1. Designing schematic and layout
2. Developing PCB from PCB maker
3. Mounting PCB
4. Fine-tuning values of passives for optimised performance
5. Ordering all the components of the module and manufacturing it
6. RF tests and certifications

Designing an RF section with chipset can take 3–6 months. It also requires multiple resources such as RF designers, supply chain and multiple service partners such as PCB makers and EMS companies. This approach is suitable for a very high volume production, but is not desirable for prototyping and low-volume production.

Modules are designed for fast time to market. Adding connectivity using modules does not require any prior RF expertise. Wireless connectivity is easy, like a modular drop-in add-on; as the designers get a readily available RF section, the implementation using modules is very quick. So designers can bring their product into market very quickly. This is particularly very important for prototyping and low-volume production.

Certification

Virtually any electronic device undergoes general emission testing. Besides, devices that have RF sections are also treated as intentional radiators. So they require additional certification to ensure they do not emit more power than allowed, or disturb other devices or frequency bands. There is no global certification, and every country or region has their own standards. Often the standards are similar, but they still require an application and associated processes.

Most of the RF technologies such as BLE, Wi-Fi and GPRS comply with a standard defined by those specific organisations. So they go under those certifications also.

Let us understand certification aspect using the devices under consideration — BlueNRG SoCs and BlueNRG-M2SA module from STMicroelectronics.

A Bluetooth Low Energy enabled device needs to be certified by Bluetooth SIG — a governing body of Bluetooth — to use the Bluetooth logo. It also needs to get RF certification from different countries and regions. Certification defined by some of the countries and regions includes FCC (US), RED (Europe), WPC (India), IC (Canada), SRCC (China) and Type (Japan).

As modules are already tested and certified as radiated devices, designs implemented using modules do not require further radiated device certification and will be treated as yet another electronic device. Table 1 includes a comparison of cost using chipset and module.

Table 1.

The process of certification is time-consuming, tedious and costly. If the volume of production is large the cost can be amortised by economy of scale, but not efficiently by small-scale production.

Cost

Some of the elements of cost have already been discussed in this article, with examples including:

• Cost of circuit design
• Cost of designers, supply chain and production
• Cost of certification
• Cost of opportunity

In general, these costs are justified if volume of production is above 100–150K pcs per year, or the product form factor does not allow a dedicated module to be incorporated.

Conclusion

Chipset approach should be adopted if the end device form factor cannot adjust module or production volume is very large to justify cost of design, production and certification. Modules should be preferred if a company wants to focus on its core competencies and avoid hassles of RF design. Modules are also preferred for prototyping and low-volume production.

STMicroelectronics is a leader in low-power RF technologies and provides a wide range of chipsets and modules for a range of usage scenarios as discussed in this article. Many of the company’s chipsets and modules come with 10 years of longevity commitment, meaning that if a company utilises these components in their design then STMicroelectronics will continue to supply those components for 10 years from the launch of the products or offer pin2pin replacements.

Top image credit: ©denisismagilov/Dollar Photo Club

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