Cortex-M3 is good news for medical systems – ON Semi

High levels of accuracy are paramount in medical sensing applications and processor cores such as ARM’s Cortex-M3 enable easier modification of established designs, writes Jakob Nielsen, senior manager, consumer health at ON Semiconductor

Through employment of lightweight portable electronic devices, it is possible for blood glucose, pulse oximetry, electrocardiogram and various other forms of physiological data to be acquired and subsequently analyzed remotely. Non-invasive monitoring of a patient’s ongoing condition can be carried out from the comfort of their home, ensuring against any added distress to the patient, as well as curbing costs associated with such activities.

High levels of accuracy are paramount in medical sensing applications as any deviation from this could have dire consequences for the patient involved. More rapid evolution of product technology and advances in measurement techniques also mean that the time between new models being introduced (and therefore chip re-spins) has been shortened significantly.

Processor cores such as ARM’s Cortex-M3 (first introduced in 2004) enable easier modification of established designs.

ON Semiconductor developed the Q32M210 precision mixed-signal microcontroller (MCU), specifically for portable sensing applications requiring high accuracy, predictable operation, and power efficiency.

The small form-factor MCU integrates a programmable 32-bit Cortex-M3 core, complemented by a high-precision analog front-end, two true 16-bit low-noise analog-to-digital converters, high-accuracy voltage reference and three 10-bit digital-to-analog converters.

The Q32M210 MCU consumes less than 1mA when the analog front end is active and the core is running at a speed of 1MHz. While in standby mode it requires just 26µA, and in sleep mode, with the real-time clock active, this is reduced further still to less than 750nA.

The Cortex-M3 core processing architecture offers 256kbyte of flash memory for program/user data storage, plus 48kbyte of SRAM for storing intermediate data during operation. To maintain the integrity of the program code and logged patient data, error checking/correction circuitry can be incorporated on-chip, allowing single-bit errors on the Flash memory to be corrected and triggering of alerts if errors of two-bits or greater occur.

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Figure 1: Q32M210 Functional Block Diagram

Application in Blood Glucose Monitors
It is estimated that there will be close to 438 million people suffering with diabetes by 2030 (according to the World Diabetes Foundation). Blood glucose monitors are consequently seeing greater uptake. These generally work on the principle of a blood droplet being applied to a test strip and assessment of the droplet’s electrical characteristics determining glucose levels. As the chemistry utilized by strips vary, it is important that monitors can be quickly and easily re-configured. System-on-chip (SoC) microcontrollers like Q32M210 achieve this through their fully programmable cores.

By combining such cores with software configurable analog front-ends, solution flexibility is further improved. A blood glucose monitor only needs to be in full operation for a few minutes each day, so having active, standby and sleep modes incorporated into the monitor’s MCU means it will not draw power unnecessarily. In a typical blood glucose monitoring application, with the core running for 5 mins/day, the Q32M210 microcontroller enables the monitor to operate for nearly two years on a single battery.
The use of an SoC approach also results in smaller form factors, benefiting the patient, as carrying the monitor around will not be as great an inconvenience. Integration of a wide range of analog and digital functions in a single chip reduces overall component count and lowers bill of materials cost for device manufacturers.

The software re-configurability aspect that the Cortex-M3 processor possesses facilitates full code portability, so that a broader range of different strip chemistries can be addressed through one semiconductor platform, plus new features can be added as required.

Furthermore, Q32M210’s on-chip power supervision with dedicated brownout protection circuitry and low battery detection, mean that predictable operation is maintained under all battery conditions. These attributes will help to improve the quality of life of those suffering with afflictions such as diabetes.

The flexibility, scalability and portability of precision mixed-signal MCUs based on the proven, widely used programmable Cortex-M3 cores allow the requirements of portable medical applications like blood glucose monitoring to be met. A highly adaptable measurement solution can be created so that a range of products covering different price/performance criteria can stem from one generic platform. Equipping the MCU with multiple operating modes leads to considerable power savings being realized and battery life being extended.

Tags: ARM, Cortex, healthcare, medical, ON, processors

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