Use Advanced Analog Front-Ends and Security to Bring Benefits of AI to Medical Point of Care

Artificial intelligence (AI) is already extracting additional insight from patient tests and trial data, improving diagnoses, and enhancing predictions and trend analysis. The next step is migrating AI-driven medical testing and sample analysis from the laboratory into the physician’s office, the clinic, or the home. This point-of-care (PoC) approach enables rapid assessment of medical conditions, reduced patient burden, and more frequent testing to provide more granular data and identify worrisome trends sooner.

Realizing AI-driven PoC requires versatile, application-optimized ICs with advanced analog front-ends (AFEs) to interface with biosensors for the necessary data-acquisition measurements. These ICs must address the unique attributes of sophisticated electrochemical, biological, and related measurements, including accuracy, low power, and highly integrated functions. They must also be supported by advanced security technology to ensure data privacy.

This article examines the shift to PoC and its design implications. It then describes widely used AFE measurement scenarios and introduces example solutions from Analog Devices to meet PoC measurement and security requirements.

Why now for PoC?

The driving forces for increased PoC testing and sample processing include the demand for more and better medical diagnostics to improve individual health prospects and the need to develop population-based insight into aging, illness, and disease. Regulatory mandates encourage and even demand more tests, and these must be done at a lower cost with reduced test and waiting time. There is also a trend towards more local PoC at a clinic or at home to minimize patient disruption and expense, requiring simple yet powerful instrumentation.

At the same time, AI is rapidly evolving to enable this data to be used for deeper analysis and forecasting.

These combined factors are creating demand and opportunity for sophisticated IC-based circuitry optimized for the unique needs of medical-test data acquisition and management. Such ICs are the front-line interface between patient fluids and the systems needed to capture, record, assess, and report the resultant data from various sensors (Figure 1).

Figure 1: Analog and related electronics provide the critical interface between a patient’s vital signs and fluids and the associated PoC instrumentation and data systems. (Image source: Analog Devices)

Diverse application-focused ICs address challenges

Some examples clearly illustrate this situation:

Example #1: Pulse oximetry and heart-rate monitors:

Blood oxygen saturation level (SpO₂) and heart rate are among the basic critical health measurements. The first parameter provides the most dramatic example of how optics and electronics have changed PoC expectations. Historically, the only way to measure SpO₂ was for a nurse to draw a blood sample and send it to a lab for testing.

Now, using the electro-optical technique perfected a few decades ago, a fingertip LED, photosensor, and algorithms provide a quick do-it-yourself (DIY) reading in seconds. As an added benefit, the same LED-photosensor arrangement provides heart-rate information.

Advances in LED-plus-photosensor systems offer additional performance and capabilities. ICs such as the MAX86171 (Figure 2, top), an ultra-low-power optical data-acquisition system with both transmit and receive channels, are tailored to these applications based on their functionality and specifications. Despite their internal complexity, only a few discrete components are needed in an application (Figure 2, bottom).

Figure 2: The MAX86171 multichannel, ultra-low-power, optical data-acquisition system (top) leverages its high level of internal integration to simplify external wiring complexity and the need for passive support components (bottom). (Image source: Analog Devices)

On the transmitter side, the MAX86171 has nine programmable LED driver output pins connected to three high-current, 8-bit LED drivers. On the receiver side, the MAX86171 has two low-noise, charge-integrating front-ends with ambient light cancellation (ALC) circuits, resulting in a high-performance, highly integrated, optical-based data-acquisition system.

In addition to SpO₂ and heart rate data, the IC can assess heart-rate variability, body hydration, muscle and tissue oxygen saturation (SmO₂ and StO₂), and maximum oxygen consumption (VO₂ max).

Note that the figures of merit and priorities for medical applications differ from those for non-medical situations. As the light levels are usually relatively low, the absolute noise floor of the optical front-ends is the critical parameter rather than the signal-to-noise ratio (SNR).

While bandwidth and sampling rates are very low, since parameters of interest do not vary at multi-kilohertz rates in the biological world, the complex analog nature of patients and the signals mandates different sets of priorities in specifications. These include high sensitivity, wide dynamic range, and low noise to succeed in the changing, non-fixed ambient environment where the patient’s skin and internal organs continually shift to change contact area and force, even slightly. They also do so in the presence of various types of interfering “noise” and variations, further complicating matters.

To meet the application requirements, the MAX86171 features a dynamic range between 91 and 110 decibels (dB) depending on test arrangement, a resolution of 19.5 bits, a dark current noise of less than 50 picoamperes (pA) (RMS), and an ambient light rejection figure of better than 70 dB at 120 hertz (Hz).

Example #2: Potentiometry, amperometry, voltammetry, and impedance measurements:

Electrical engineers are comfortable with measuring voltage, current, and impedance, along with their relationships, by choosing from a wide variety of standard instrumentation. However, these measurements have unique requirements and constraints in a chemical and biological setting and present distinct scenarios:

• Potentiometry: using a potentiostat to measure the electrical potential between two electrodes to determine the concentration of a substance in a solution
• Amperometry: using an amperometric arrangement to detect ions in a solution based on electric current or changes in electric current
• Voltammetry: where a specific voltage profile is applied to a working electrode as a function of time, and the current produced by the system is measured, usually via a potentiostat
• Impedance: measuring the voltage and current relationship of skin and body

To assess these parameters, the AD5940 provides a wide range of functionality and interface options in a 56-ball WLCSP measuring 3.6 × 4.2 millimeters (mm) (Figure 3). This low-power AFE is designed for portable applications that require high-precision electrochemical techniques such as amperometric, voltammetric, or impedance measurements.

Figure 3: The AD5940 AFE incorporates the sophisticated functions needed for precise, low-power amperometric, voltammetric, or impedance measurements. (Image source: Analog Devices)

The AD5940 has two excitation loops and one common measurement channel. The first loop consists of a dual-output string, a digital-to-analog converter (DAC), and a low-noise potentiostat, and it can generate signals from 0 Hz to 200 Hz.

One output of the DAC controls the noninverting input of the potentiostat, and the other controls the noninverting input of the transimpedance amplifier (TIA). The second loop consists of a 12-bit DAC capable of generating excitation signals up to 200 kHz.

On the input side, there is a 16-bit, 800 kilosample per second (kS/s) analog-to-digital converter (ADC) with input buffers, an antialias filter, and a programmable gain amplifier (PGA). A multiplexer selects input channels for external current and voltage inputs and internal channels for supply voltages, die temperature, and reference voltages.

The current inputs include two TIAs with programmable gain and load resistors for measuring different sensor types. The first TIA measures low-bandwidth signals, while the second TIA measures high-bandwidth signals up to 200 kHz.

Users of ICs that offer this level of integration and versatility benefit from evaluation kits that go beyond the IC itself. For the AD5940, the EVAL-AD5940BIOZ Electrocardiography (ECG/EKG) Sensor Arduino Platform Evaluation Expansion Board provides a familiar development environment (Figure 4).

Figure 4: The EVAL-AD5940BIOZ electrocardiography (ECG/EKG) sensor Arduino Platform evaluation expansion board simplifies the challenge of using and assessing the AD5490 when making the subtle, low-level measurements it is designed to provide. (Image source: Analog Devices)

Each AD5940 evaluation board targets a particular end-application measurement objective. The Arduino-like board configures and communicates with the AD5940 through the SPI peripheral. A graphical user interface (GUI) tool for measurements with graphing and data-capture capabilities is available for initial evaluation. Many example projects written in embedded C include instructions on how to set the programming environment and run the examples.

Example #3: Data security and authentication:

Data stored in diverse and unsecured locations and transmitted using wireless near-field communication (NFC) links raises serious issues related to data security, authenticity, prevention against hacking, and the risk of reuse, misuse, and counterfeit samples or cartridges.

To address these concerns, the MAX66250 Secure Authenticator (Figure 5, top) provides robust countermeasures, with all stored data cryptographically protected from discovery. It is compatible with NFC-enabled embedded systems (Figure 5, bottom), where the risk of unauthorized access is higher.

Figure 5: The MAX66250 Secure Authenticator (top) provides multiple levels of advanced data security and authentication support; it also incorporates an NFC interface (bottom) for wireless data transfer. (Image source: Analog Devices)

The secure authenticator combines FIPS 202-compliant Secure Hash Algorithm (SHA-3) challenge-and-response authentication with secured EEPROM. The device provides a core set of cryptographic tools derived from integrated blocks, including an SHA-3 engine, 256 bits of secured user EEPROM, a decrement-only counter, and a unique 64-bit ROM identification number (ROM ID). The unique ROM ID is a fundamental input parameter for cryptographic operations and serves as an electronic serial number within the application. The device communicates over an RF interface compliant with ISO/IEC 15693.

Example #4: Motion/motor control:

Many PoC devices and stations require carefully controlled motion to convey a test strip or test tube between stations, combine and transfer reagents, or add or release precise amounts of liquids and perform pipetting. These applications often require precise micro-stepping and smooth stop, start, and ramp generation to provide high-resolution and vibration-free movement for quick, precise, reliable, quiet, reproducible, and energy-efficient motion.

The Trinamic TMC5072-LA-T single/dual-channel stepper-motor controller and driver IC (Figure 6, top) with serial communication interfaces is suited to these applications. When wired for parallel operation, it offers coil-current drive capability of 1.1 A/1.5 A peak per motor and 2.2 A/3 A peak for one motor.

For basic operation, the companion TMC5072-BOB eval kit (Figure 6, bottom), which includes an onboard TMC5072, connects to an Arduino Mega using a single-wire universal asynchronous receiver/transmitter (UART). A graphical user interface (GUI) provides tools for easily setting parameters, visualizing data in real time, and developing and debugging stand-alone applications.

Figure 6: The TMC5072-LA-T single/dual-channel stepper-motor controller and driver IC (top) provides precision performance and smooth operation; it is supported by the TMC5072-BOB eval kit (bottom). (Image source: Analog Devices)

The TMC5072 combines flexible ramp generators for automatic target positioning and offers noiseless operation, maximum efficiency, and high motor torque. The 7 mm × 7 mm IC offers other advanced features:

• StealthChop for extremely quiet operation and smooth motion
• SpreadCycle highly dynamic motor-control chopper
• DCStep for load-dependent speed control
• StallGuard2 high-precision sensorless motor-load detection
• CoolStep current control for energy savings up to 75%

Conclusion

A combination of technological advances has the potential to bring the benefits of AI to localized medical PoC. This requires integrated, application-focused ICs such as advanced AFEs and data security blocks. Analog Devices offers many choices of high-performance, low-power devices optimized for these applications that meet the technical, medical, and regulatory requirements.