Continuous glucose monitors (CGMs) have reshaped diabetes management by delivering real-time glucose readings, freeing patients from frequent finger-stick testing. These compact, wearable devices not only enhance quality of life but also allow clinicians to adjust therapy based on accurate, continuous data streams.
Behind this innovation lies a complex engineering challenge: Designers must develop a device that operates safely and reliably on a micro-scale power budget, fits within a compact, body-worn form factor, and maintains precise sensing accuracy in all conditions. Every component, whether analog, digital, power management, or protective, must contribute to long-term reliability and patient comfort. In many designs, even microamp-level leakage or a single mechanical failure point can limit device lifetime or compromise reliability.
Magnetic sensing, particularly tunnel magnetoresistance (TMR) technology, offers a practical approach for implementing sealed, contactless activation and other event-based state-detection functions without materially impacting battery life. This article examines the role of magnetic sensing in CGM architectures, explains the operating principles of TMR switches, and discusses their applications for activation, alignment confirmation, and auxiliary-state detection. Design tradeoffs, implementation considerations, and package-level constraints are also explored to help engineers evaluate when TMR sensing is appropriate in CGM designs.
The role of CGMs in connected healthcare
CGMs are central to modern diabetes care. They measure glucose concentration in interstitial fluid using a sensor inserted beneath the skin, which transmits readings wirelessly to a smartphone, insulin pump, or cloud-based management system.
The benefits of CGMs are well-established: reduced glycemic variability, better HbA1c levels, and fewer hypoglycemic episodes. As the technology matures, CGMs are now prescribed for a wider population, including patients with Type 2 diabetes, gestational diabetes, and even pre-diabetic conditions, expanding their relevance across preventive medicine and chronic care.
From an engineering perspective, these devices embody the broader trend toward connected, always-on healthcare systems, in which safety, data integrity, and energy efficiency are equally critical.
System architecture and design constraints
A typical CGM system includes five key components:
- The glucose sensor and analog front end amplify and condition microvolt-level signals from the biosensor.
- The microcontroller processes data, handles algorithms, and manages wireless communication via Bluetooth Low Energy or proprietary protocols.
- The power-management circuitry regulates energy from a small rechargeable or disposable battery.
- The wireless interface communicates readings to companion devices or cloud platforms.
- Temperature sensing, protection, and activation circuits safeguard operation and enable user interaction.
These modules must function continuously for seven to 14 days on a single charge, all while exposed to motion, sweat, temperature fluctuations, and electrostatic discharge (ESD). Component size, thermal behavior, and power efficiency dictate patient comfort and product usability.
Engineering challenges unique to CGM design
Engineering challenges in CGM design include achieving ultra-low power consumption and extreme miniaturization in limited PCB space while maintaining electrical safety/isolation and environmental resilience. Designs must also meet stringent regulatory compliance requirements:
- Ultra-low power consumption: Every microamp of leakage current reduces battery life. Components must have negligible quiescent draw.
- Miniaturization: Patch-style and implantable CGMs allow only millimeters of PCB space, demanding small-package, high-performance devices.
- Electrical safety and isolation: Circuit faults must be contained quickly to protect the patient and device integrity.
- Environmental resilience: Resistance to sweat, vibration, and humidity ensures consistent operation throughout the wear cycle.
- Regulatory compliance: Designs must comply with IEC 60601, ISO 13485, and 21 CFR 820 requirements for safety, quality, and EMC performance.
Meeting these demands requires careful component selection and system-level integration.
Magnetic activation for sealed, contactless operation
Power-on and reset functions are fundamental in wearable devices. Traditional mechanical pushbuttons introduce contamination paths, wear over time, and complicate waterproofing. The activation circuit keeps energy consumption during the shelf life to a minimum, ensuring the device remains safe to operate after 24 months. Magnetic activation provides a contactless alternative that enhances durability and hygiene.
Three magnetic-switching technologies are available: reed relays, Hall-effect sensors, and TMR switches. Each presents tradeoffs in power consumption, sensitivity, and footprint (see Table 1 for a comparison). In practice, the key differentiator is standby current, whereby TMR operates in the nanoamp range, versus milliamps for typical Hall-effect devices.
TMR sensors offer a highly effective combination of performance characteristics for CGM applications: nanoamp-to-microamp power levels, compact LGA packages, and omnipolar detection for flexible magnet placement.
For example, Littelfuse TMR magnetic switches detect flux changes as low as 9 Gauss and draw only 160 nA in low-speed mode. Their contactless operation enables features such as automatic power-on when the device is applied to the skin or activation during packaging removal. Because they have no moving parts, TMR switches are immune to vibration and moisture, providing a lifetime of tens of billions of switching cycles.
By eliminating mechanical interfaces, engineers reduce mechanical failure risk, improve sealing, and extend battery life—all critical for patient-worn electronics. This approach makes TMR switches particularly attractive for designs in which activation must remain available throughout storage and use without impacting overall system power budgets.
Thermal monitoring and patient safety
Temperature sensing plays multiple roles in CGM design:
- Electronic safety monitoring detects abnormal heat buildup from circuit faults or battery degradation.
- Patient protection prevents surface temperatures that could irritate or burn the skin.
- Sensor compensation adjusts for temperature-dependent enzymatic reactions that influence glucose readings.
Compact NTC thermistors, such as Littelfuse’s 0803-KR, 0603-RB, and 1206-LR series, offer ±5% accuracy in packages as small as 1.6 × 0.8 × 1.0 mm. Engineers often use multiple thermistors: one near the biosensor for reaction compensation and another near the battery or power-management circuitry for thermal safety monitoring.
Precise thermal feedback not only protects users but also enhances measurement accuracy, contributing directly to clinical reliability.
The number, location, and role of temperature sensors vary by CGM architecture, but designers generally distinguish between temperature sensing for safety monitoring and temperature sensing used for measurement compensation.
Integrating protection and sensing for reliable operation
Effective CGM design blends protection, sensing, and activation elements into a cohesive system. Integration offers several key benefits:
- Extended battery life through ultra-low leakage protection and sensing components
- Improved mechanical reliability by eliminating moving parts and exposed contacts
- Simplified certification when using pre-qualified components compliant with medical standards
- Enhanced user confidence through consistent, failure-free performance
When these design principles are applied, engineers can focus on refining algorithms, connectivity, and patient-experience features rather than troubleshooting hardware faults.
Regulatory and compliance considerations
Every CGM must meet stringent international standards to ensure safety and performance. Table 2 outlines the most relevant to electronic subsystems.
Choosing electronic components with existing documentation for these standards can streamline risk management files and accelerate regulatory review.
Future trends in CGM and wearable design
As wearable healthcare expands, designers are targeting a reduction in device size, longer lifetimes, multi-sensor integration, and cloud-connected analytics. Each evolution places an even greater emphasis on power efficiency and electrical safety.
Emerging technology trends include:
- The integration of multi-parameter sensors (glucose, lactate, temperature, and hydration)
- The use of energy-harvesting or inductive-charging technologies to extend operating life
- The implementation of advanced protection monitoring, such as built-in diagnostics for ESD or fuse status
- The development of biocompatible, flexible electronics to further improve patient comfort
Component suppliers that offer medically focused design support and validated protection portfolios will play a crucial role in accelerating these innovations.
CGMs exemplify the convergence of biomedical science and advanced electronics. To achieve reliable, always-on operation in a body-worn form factor, engineers must carefully manage power, protection, and sensing interactions at every design level.
By integrating TMR magnetic switches for contactless activation, NTC thermistors for safety and compensation, low-leakage ESD/TVS diodes for transient protection, and miniature medical-grade fuses for fault isolation, developers can meet the strict performance and safety requirements of modern medical devices.
The result is a new generation of CGMs that are smaller, more power-efficient, and more reliable, meeting the practical constraints of wearable system design while enabling accurate, continuous monitoring.
About the author
Marco Doms is a senior manager of business development new platforms at Littelfuse Inc. Doms studied electrical engineering and holds a Ph.D. in MEMS. He was the head of R&D at two other sensor companies before joining Littelfuse in 2022. Doms has a long history in position sensors (especially xMR) and managing R&D and Innovation teams—from chip to system level. At Littelfuse, he started as an innovation manager, led the EBU Advanced Development team, and introduced an Innovation/Idea Management process. In his current role, Doms is responsible for several platforms with entirely new products or product features that require additional internal and customer coordination.
Marco Doms is senior manager of business development for new platforms at Littelfuse Inc.
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