ADI’s Latest Analog Front End Measures Vitals in Its Smallest Package Yet
Embedded in a wearable system, ADI's new analog front end is designed to level up bioimpedance monitoring—a way to monitor various medical conditions and help doctors come to a more precise diagnosis.
Analog Devices, Inc. (ADI) recently released a low-power, high-performance analog front end (AFE) built for wearable bioimpedance monitoring. Bioimpedance analysis is a non-invasive, low-cost analysis essential to diagnose renal, cardiac, neural, pulmonary, and infectious diseases. Medical professionals are currently exploring this approach for body composition measurements required for disease diagnosis.
Integrated into wellness wearables and medical-grade patches, the recently-released low-power, high-performance BioZ (bioimpedance) analog front end (AFE) MAX30009 promises clinical-grade vital sign measurements for patient assessment.
A simplified block diagram of MAX30009.
This article explores the capabilities of this product from ADI, highlighting some design-level specifications of the device. We'll also compare the new release with an existing AFE from ADI released a few months ago.
MAX30009 for Bioimpedance Analysis
The low power capability of the MAX30009, down to 250 µW at 1.8V AVDD, reduces its draw on tiny batteries, extending its operational life. Additionally, ADI says the MAX30009 comes in a smaller size and offers higher performance than existing BioZ devices; MAX30009 offers up to a 30% smaller design due to high-level design integration, reducing its size to 2.03 mm x 2.03 mm and significantly improving patient comfort.
Example of the BioZ AFE in a medical-grade chest patch.
The MAX30009 has the ability to measure from both I and Q channels simultaneously. It also comes in two-electrode and four-electrode configurations and offers sample rates and frequencies up to 4 ksps and 891 kHz, respectively. Other key features of the MAX30009 BioZ include:
- High-resolution analog-to-digital converters (ADCs)
- High impedance of over 1GΩ for ultra-low common to differential-mode conversion
- High input AC dynamic range exceeding 1000mVP-P
- Programmable sine-wave stimulus
Designers can incorporate the MAX30009 BioZ into various wearable medical devices for a range of applications, including bioimpedance analysis/spectroscopy (BIA/BIS) and automatic external defibrillation (AED). Other applications include multi-frequency body composition analysis, respiration rate monitoring, body composition and fluid analysis, and impedance cardiography/plethysmography (ICG/IPG).
Key Design-level Specifications
Some key design-level specifications for the MAX30009 BioZ include a current stimulus circuit-incorporated transmit channel, a component-integrated receive channel, a high-precision calibration port, and an advanced modification capability. ADI says the availability of injected body currents is useful for applications such as BIA/BIS, ICG, and IPG, by incorporating an independent current stimulus circuit into the transmit channel of the MAX30009 BioZ.
The stimulus circuit comes in four-electrode (tetrapolar) and two-electrode (bipolar) options, providing a programmable current within the wide frequency and magnitude ranges of 16 Hz to 806 kHz and 16nARMS to 1.28mARMS, respectively.
Stimulus generator for the MAX30009 BioZ.
ADI also asserts that the MAX30009 offers a high-input impedance and a low-noise receive channel, which includes a high common-mode rejection ratio (CMRR) programmable gain, high-resolution analog-to-digital converters, and several low- and high-pass filter options. As mentioned, the transmit channel also offers a simultaneous I and Q measurement that provides reactance and resistance measurements.
The receive channel of the MAX30009 BioZ.
The four-wire external precision reference resistance-based calibration port of the MAX30009 is built for accurate BIA/BIS and AED body impedance measurements. Although this four-wire calibration port supports multiple calibration resistances, designers can also opt for internal trimmed load resistors for calibration. However, these load resistors may be less accurate than the MAX30009's external reference resistor.
Programmable resistor load.
The MAX30009 also offers designers high flexibility in wearable designs with its easily adjustable software registers. ADI fosters this flexibility by allowing digital data storage into a 256-word FIFO, which allows engineers to connect the MAX30009 to a microcontroller or processor through a shared I2C or serial peripheral interface (SPI) bus.
MAX30009 vs. MAX86178
ADI previously released the MAX86178 AFE in September 2021. The MAX86178 AFE promised to significantly simplify the design of wearable remote patient monitoring (RPM) devices and offer low-cost and improved healthcare delivery. Although both AFE releases perform similar vital sign measurement and monitoring-related functions, they differ in several areas, including package size, power consumption, and specific applications.
While the MAX86178 AFE comes in a 49-bump wafer-level package (WLP), measuring 2.77 mm x 2.57 mm, the MAX30009 comes in a 2.03 mm x 2.03 mm, 25-bump WLP. Moreover, the MAX86178 AFE integrates optical, electrocardiogram (ECG) and bio-impedance measurement systems to measure four common vital signs, including blood-oxygen saturation (SpO2), electrocardiogram, respiration rate, and heart rate. The MAX30009, on the other hand, is designed for a wider range of bioimpedance applications, including BIA/BIS, ADE, ICG, galvanic skin response/electrodermal activity, and non-invasive hemodynamic monitoring.
With a minimum supply voltage (VSUPPLY(min)) of 1.1 V and a maximum supply voltage (VSUPPLY(max)) of 3.6 V, MAX30009 offers lower power consumption than MAX86178 with VSUPPLY(min) and VSUPPLY(max) of 2.3 V and 5.5 V, respectively.
All images used courtesy of Analog Devices.