CGM Industry Solutions

Continuous Glucose Monitoring (CGM) Device Principles and Electromagnetic Compatibility Solutions

CGM Product Working Principle

Core Working Logic

Continuous glucose monitoring (CGM) devices are medical devices that monitor blood glucose levels in real time. They detect the glucose concentration in interstitial fluid through a subcutaneous glucose sensor, indirectly reflecting the body’s blood glucose level. Compared to traditional finger-prick blood sampling, CGM offers advantages such as real-time, continuous, and painless monitoring, providing comprehensive blood glucose data for diabetic patients and aiding in blood glucose management.

Its core relies on the enzymatic electrochemical principle of biosensors: glucose oxidase within the sensor oxidizes glucose to generate hydrogen peroxide. The hydrogen peroxide undergoes an electrochemical reaction at the electrodes, generating a current signal. The signal strength is directly proportional to the glucose concentration, thus converting blood glucose concentration into an electrical signal.

The converted electrical signal is amplified, filtered, and then transmitted wirelessly via Bluetooth or other technologies to terminals such as smartphones or dedicated receivers. The terminal converts the signal into blood glucose values, presenting them in graphical and numerical form, allowing users to intuitively understand blood glucose trends.

Circuit Composition and Functions

A typical CGM circuit comprises four core components: a sensor circuit, a signal processing circuit, a wireless transmission circuit, and a power supply circuit. These modules work together to achieve the device’s blood glucose monitoring and signal transmission functions:

1. Sensor Circuit: Performs the basic conversion from glucose concentration to an electrical signal;

2. Signal Processing Circuit: Equipped with an AFE IC containing ADC and SPI, it amplifies, filters, and performs analog-to-digital conversion on the weak electrical signal output from the sensor, adapting it to the processing requirements of subsequent circuits;

3. Wireless Transmission Circuit: Relying on an MCU containing SPI and ANT, it transmits the processed signal externally;

4. Power Supply Circuit: Provides a stable and continuous power supply for the entire device system.

Electromagnetic Compatibility (EMC) Standards for CGM Products

Electromagnetic compatibility refers to the ability of a device to operate normally in its own electromagnetic environment without causing unacceptable electromagnetic interference to other objects in the environment. The formulation of relevant standards aims to ensure the operational stability of the device in its electromagnetic environment while avoiding interference with other devices. As a medical device, the CGM must comply with multiple international and domestic standards.

International Standards

1. International Electrotechnical Commission (IEC) Standard: IEC 60601-1-2, which clearly defines the electromagnetic compatibility (EMC) requirements for medical electrical equipment, covering two main dimensions: equipment immunity and self-disturbance suppression. It includes test requirements and limits for various immunity parameters such as electrostatic discharge, radio frequency electromagnetic field radiation, and electrical fast transient/burst.

2. Relevant Standards from the European Telecommunications Standards Institute (ETSI): These standards are designed for the EMC of telecommunications equipment, imposing strict requirements on radio frequency emissions and immunity to ensure CGM’s compliance in the European market and guarantee its stable operation in complex electromagnetic environments without interfering with other communication equipment.

Domestic Standards

1. Registration Classification: Belongs to the category of dynamic blood glucose/glucose monitoring devices in the Medical Device Classification Catalog, subject to dual regulatory requirements for implantable sensors and active medical devices;

2. National Standard: GB9706.102-2021, based on IEC60601-1-2, and combined with domestic actual needs, clarifies the electromagnetic compatibility requirements and test methods for medical electrical equipment including CGM;

3. Industry Standard: Referencing relevant clinical application guidelines for blood glucose monitoring, focusing on calibration algorithms, signal stability, alarm thresholds, etc., while complying with the electromagnetic compatibility requirements of the YY0505 series of medical electrical equipment.

Common Operational Problems of CGM Products

Signal Interference Problems

In complex electromagnetic environments (such as near large medical equipment or electronic communication base stations), the device is susceptible to external electromagnetic signal interference, leading to inaccurate blood glucose data, abnormal fluctuations, and even close contact between a mobile phone and the device can cause deviations in the displayed blood glucose value. The core reason is that the device’s signal transmission frequency is close to that of common electromagnetic interference sources, easily causing resonance or signal superposition. Simultaneously, internal circuit design defects, such as inadequate shielding and improper signal line layout, further increase the risk of interference.

Power Supply Stability Issues

Unstable power supply can cause sudden shutdowns, restarts, or the device to stop working despite a normal power level display. During charging, slow charging or failure to fully charge may also occur. This is mainly due to quality issues with power circuit components, such as battery aging, charger malfunctions, and capacitor leakage. Furthermore, insufficient performance of the power management chip and unreasonable power control software algorithms can also lead to inaccurate battery status detection and charging control failure.

Sensor Failure Issues

Sensors are prone to problems such as increased measurement errors, shortened lifespan, signal interruption, or inability to start, resulting in significant deviations between monitored and actual blood glucose values. On the one hand, sensors are in prolonged contact with human skin and subcutaneous interstitial fluid, making them susceptible to corrosion and contamination by biological fluids, affecting performance. On the other hand, poor sensor manufacturing processes and substandard material quality, such as oxidation of electrode materials after long-term use, can obstruct signal transmission.

Software System Failures

The device’s operating system or supporting applications are prone to crashes and freezes, preventing users from viewing blood glucose data correctly. Data storage and transmission errors also exist, such as data loss, incomplete transmission, or delays. The core cause is software programming vulnerabilities and data processing algorithm defects. For example, low algorithm efficiency when processing large amounts of blood glucose data can lead to excessive memory usage and freezes. Furthermore, poor software compatibility with different receiving devices can also cause abnormal data transmission.

Insufficient Anti-static Capacity

Static electricity generated by the human body in a dry environment (such as from friction from synthetic clothing) can cause display flickering, data errors, and device restarts when it comes into contact with the device. This is because the device’s casing and internal circuitry lack anti-static design and effective electrostatic shielding and grounding measures are not implemented. Accumulated static charge can damage internal electronic components, causing device malfunction.

Electromagnetic Compatibility Testing Requirements for CGM Products

To ensure the electromagnetic compatibility performance of CGM equipment, multi-dimensional immunity and interference emission tests are required. Each test item targets different electromagnetic interference scenarios to verify the equipment’s operational stability and electromagnetic interference control capabilities:

1. Electrostatic Discharge Immunity Test: Simulating electrostatic discharge from a human body/object to the equipment, a specified voltage is applied to the equipment casing and interfaces through contact and air discharge methods. The test observes whether the equipment exhibits data errors, crashes, or other abnormalities, verifying its operational stability under electrostatic shock.

2. Radio Frequency Electromagnetic Field Radiation Immunity Test: Placing the equipment in a radio frequency electromagnetic field, gradually increasing the electromagnetic field strength and frequency, and testing whether the blood glucose monitoring function is affected and whether the data display is accurate, verifying the equipment’s resistance to radio frequency interference.

3. Electrical Fast Transient/Bulk Immunity Test: Injecting electrical fast transient/burst immunity into the equipment’s power and signal ports, checking whether the equipment can maintain normal operation under short-term pulse interference, without malfunctions or equipment damage.

4. Surge Immunity Test: Simulates surge impacts from lightning strikes and electrical switch operations, applying specified surge voltages and currents to power and signal ports to verify the equipment’s ability to withstand surge impacts and whether the circuit remains intact and functions normally after an impact;

5. Conducted Interference Test: Measures electromagnetic interference signals emitted by the equipment through power and signal lines, ensuring signal strength is within standard limits to avoid interference with the power and signal lines of other equipment;

6. Radiated Interference Test: Detects electromagnetic interference signals radiated by the equipment into the surrounding space, assessing its impact on the surrounding electromagnetic environment and ensuring that the equipment does not interfere with other nearby electronic equipment during normal operation.

CGM Product Electromagnetic Compatibility (EMC) Solution

Addressing the electromagnetic compatibility issues of CGM equipment, solutions are developed from two dimensions: hardware design optimization and software algorithm improvement, taking a two-pronged approach to enhance the equipment’s anti-interference capability and electromagnetic compatibility.

Hardware Design Optimization

1. Basic Circuit and Structure Optimization

– Circuit Layout Optimization: Plan the circuit board layout rationally, separating sensitive circuits such as sensor circuits from interference-prone circuits such as wireless transmission circuits to reduce signal crosstalk; optimize signal line routing, shortening transmission paths as much as possible to reduce signal attenuation and the possibility of interference introduction;

– Shielding Design: Use a metal shielding shell or cover to comprehensively shield the internal circuits of the equipment, while separately shielding key circuit modules. The shielding layer must be well grounded to effectively block external electromagnetic interference from entering and prevent internal electromagnetic interference from leaking outwards;

– Filtering Circuit Design: Install low-pass, high-pass, and band-pass filter circuits at the power input port and signal transmission lines. For example, use a π-type filter circuit formed by connecting inductors in series and capacitors in parallel on the power lines to filter out high-frequency or low-frequency interference signals, ensuring the purity of power supply and signals.

2. Critical Interface ESD Protection
Dedicated electrostatic discharge (ESD) protection devices are configured for critical interfaces such as the lithium battery, sensors, and Bluetooth antenna. All devices utilize DFN1006 packages to provide surge and electrostatic protection, ensuring stable operation of core interfaces:

– Lithium Battery Interface: Utilizes a 3V nominal voltage, 2V discharge termination voltage coin cell lithium battery. Its voltage output is stable, with an annual capacity decay rate of ≤2%. Its small size and light weight make it suitable for precision instruments. The power interface is equipped with a dedicated ESD device for surge and electrostatic protection.

– CGM Sensor Interface: The sensor’s working electrode potential is controlled at +0.4V~+0.8V, and the reference electrode potential is stabilized at +0.197V~+0.222V, providing an electronic circuit for the electrodes. The sensor interface is equipped with a dedicated ESD device to resist surge and electrostatic interference.

– Bluetooth Antenna Interface: The Bluetooth antenna converts electrical signals into electromagnetic waves for short-range wireless data transmission. The Bluetooth module is powered by 3.3V. Dedicated ESD devices are configured for antenna-related power interfaces to provide surge and electrostatic protection.

Software Algorithm Improvements

1. Anti-interference Algorithm: An anti-interference algorithm is embedded in the device software system to perform real-time analysis and processing of the collected blood glucose signals, accurately identify and remove noise signals generated by electromagnetic interference, such as using digital filtering algorithms to optimize blood glucose monitoring data, improve data accuracy and stability, and make the displayed blood glucose values ​​more realistic;

2. Data Verification and Error Correction: During data storage and transmission, verification and error correction algorithms such as CRC (Cyclic Redundancy Check) and Hamming codes are introduced to perform real-time data verification. When data errors occur, they are detected and corrected in a timely manner to ensure data integrity and accuracy, and avoid equipment failure or medical accidents caused by data errors.

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