ST Packs the Power and Connectivity Strengths of STM32 Into a Wireless MCU Module

January 07, 2021 by Dr. Steve Arar

Designing a transceiver and antenna is no small feat. A new module from ST is designed to help small companies to spend less time on the hardware and more time on the Bluetooth LE, Zigbee, or Thread application itself.

STMicroelectronics recently announced a compact module based on the STM32WB55 wireless MCU that addresses the challenges of creating a Bluetooth LE, Zigbee, or Thread application.


STM32 module


In this article, we’ll take a look at these challenges and discuss how the new module may help small companies to spend less time on the hardware and more time on the applications they are working on. 


RF Challenges of an IoT Sensor Node

The block diagram of a typical IoT wireless sensor node is shown below.


Typical IoT wireless sensor node


The MCU collects and processes the sensor data while also running a radio frequency (RF) protocol stack. This stack sends the collected data through a radio transceiver to gateways where heavier processing and data transmission occurs. 

Designing a transceiver and antenna can impose serious challenges for a company that has little or no experience in RF design. Still, the antenna design can have a significant impact on the overall system performance and whether or not the system can pass certification testing.

Optimizing the transceiver can also be as challenging as the antenna tuning. To address these issues, many small teams usually have to outsource the process. In addition to design complexity, there is another major obstacle to adding wireless connectivity to a product: the certification cost.

Many lab tests need to be conducted to guarantee the compliance of a product with the required standards. This is a costly and time-consuming process. Spending tens or even hundreds of thousands of dollars in testing and filing can be discouraging for a small team trying to produce a low-volume product.


A Wireless MCU Can Help

A wireless MCU integrates the radio transceiver with the MCU. This significantly simplifies the design process because the designer doesn’t have to worry about connecting the MCU to the radio.

In addition to simplifying the board design and reducing the bill of materials, such an integrated approach makes the design less susceptible to interference because it employs shorter connections between the transceiver and the MCU.

Moreover, with a wireless MCU, the designer can benefit from the fact that a large portion of the design has gone through the certification tests. This allows small companies to save a lot of time and money. 


ST’s Wireless MCU: STM32WBx5

The STM32WBx5 family is essentially an STM32L4 MCU running at 64 MHz (as the application processor) and a 2.4 GHz radio implemented on a Cortex_M0+ running at 32 MHz (the network processor). While the network processor handles the wireless operations of the 2.4 GHz radio, the Cortex-M4 processor can run an application in real-time.

The STM32WBx5 family supports Bluetooth LE 5.2, IEEE 802.15.4 Zigbee, Thread and concurrent wireless standards. Moreover, this MCU family offers a number of I/Os, up to 1 MB of Flash, a Floating Point Unit (FPU), and the power saving modes that can help meet the low-power requirements of an application. 


Block diagram of the STM32WB55xx

Block diagram of the STM32WB55xx. Image used courtesy of STMicroelectronics


The FPU allows 32-bit floating-point operations in hardware. This simplifies the calculations because designers no longer need to check the overflows, which is required when using a fixed-point processor. One example application where the FPU of a Cortex-M4 based 32-bit MCU can be useful is when combining GPS, accelerometer, and gyro measurements to improve location accuracy.

In addition to the processing cores discussed above, the STM32WBx5 MCUs include the wireless IP and the balun. Another important advantage of this family is that the package is compatible with a two-layer PCB that can enable a cost-effective solution depending on the product requirements. 


ST Aims to Simplify the Process Even Further

STMicroelectronics has recently announced a compact module based on the STM32WB55 wireless MCU. The new module, STM32WB5MMG, includes a miniature antenna along with the required matching circuitry between the antenna and the receiver.


Block diagram of the STM32WB5MMG module

Block diagram of the STM32WB5MMG module. Image used courtesy of STMicroelectronics


It also incorporates built-in switched-mode power supply (SMPS) circuitry as well as frequency-control components. Integrating everything up to the antenna, the new module is said to even further accelerate the market introduction of new Bluetooth LE and 802.15.4-based IoT devices. With the STM32WB5MMG module, access to certification is even further simplified.

Addressing both the design complexity and certification cost challenges allows small teams to more easily create a Bluetooth LE, Zigbee, or Thread application. 


Optimized Footprint

The STM32WB5MMG, housed in a 7 mm x 11.3 mm package, places the pins for the main features on an external ring around the package. This makes the package compatible with a low-cost two-layer PCB when only the main features are required. As depicted below, the pads for the additional features are in the middle of the package.  



Image used courtesy of STMicroelectronics

Cyber Protection Features

Benefiting from all features of the STM32WB55 wireless MCU, the STM32WB5MMG offers secured software updates including Over-The-Air (OTA) for brand protection and device integrity, customer key storage and Proprietary Code Readout Protection (PCROP) to protect developers’ intellectual property, and Public Key Authentication (PKA) support for cryptographic protection of code and connections.  



Do you work on a small team prototyping new connected devices? What design and manufacturing challenges do you face? Share your experiences in the comments below.