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.
This article examines how properly selected sensing, protection, and activation components — including miniature magnetic switches and thermistors — help engineers design CGMs that meet demanding performance, safety, and regulatory requirements.
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 a cloud-based management system (see Figure 1).
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 prediabetic 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, where safety, data integrity, and energy efficiency are equally critical.
System Architecture and Design Constraints
A typical CGM system includes:
Glucose sensor and analog front end (AFE): Amplifies and conditions micro-volt-level signals from the biosensor.
Microcontroller (MCU): Processes data, handles algorithms, and manages wireless communication via Bluetooth ® Low Energy or proprietary protocols.
Power-management circuitry: Regulates energy from a small rechargeable or disposable battery.
Wireless interface: Communicates readings to companion devices or cloud platforms.
Temperature sensing, protection, and activation circuits: Safe-guard operation and enable user interaction.
These modules must function continuously for 7–14 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 (see Figure 2).
Engineering Challenges Unique to CGM Design
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 printed circuit board (PCB) space, demanding small-package, high-performance devices.
Electrical safety and isolation. Circuit faults must be contained quickly to protect both the patient and the 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 push buttons introduce contamination paths, wear over time, and complicate waterproofing. Activation circuit keeps energy consumption during shelf life to a minimum to guarantee safe operation of the device after 24 months of shelf life. Magnetic activation provides a contactless alternative that enhances durability and hygiene.
Three magnetic-switching technologies are available: reed relays, Hall-effect sensors, and tunnel magnetoresistance (TMR) switches. Each presents trade-offs in power consumption, sensitivity, and footprint (see Table 1).
TMR sensors offer the optimal combination for CGMs: 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 (see Figure 3).
By eliminating mechanical interfaces, engineers reduce mechanical failure risk, improve sealing, and extend battery life — all critical for patient-worn electronics.
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 the Littelfuse 0803-KR, 0603-RB, and 1206-LR series, offer ±5 percent 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 power cell 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 prequalified 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 both safety and performance. Table 2 shows the most relevant for 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 reduction in device size, longer lifetimes, multi-sensor integration, and cloud-connected analytics. Each evolution places even greater emphasis on power efficiency and electrical safety.
Emerging directions include:
Integration of multi-parameter sensors (glucose, lactate, temperature, and hydration).
Use of energy-harvesting or inductive-charging technologies to extend operating life.
Implementation of advanced protection monitoring, such as built-in diagnostics for ESD or fuse status.
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.
Conclusion
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, safer, and longer-lasting — empowering patients with accurate, connected monitoring and enabling clinicians to deliver more responsive, data-driven care.
This article was written by Dr. Marco Doms, Sr. Manager, Business Development New Platforms at Littelfuse, Inc., Chicago, IL. In his current role, he is responsible for several platforms with entirely new products or product features that require additional internal and customer coordination. For more information, visit here .
