Make wearable vital signs monitoring more accurate and easier? You should know these materials from ADI~ | Big names in DK

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After watching the video, let’s briefly summarize ADI’s solutions for healthcare:

The ADPD4100/ADPD4101 is an ideal hub for a variety of electrical and optical sensors in wearable health and fitness devices for heart rate and heart rate variability (HRV) monitoring, blood pressure estimation, stress and sleep tracking, and SpO ₂ measurement. The multiple operating modes of this new multi-parameter VSM AFE can support different sensor measurements in healthcare applications, including but not limited to photoplethysmography (PPG), electrocardiogram (ECG), electrodermal activity (EDA), body composition, respiration, temperature, and ambient light measurement.

The ADPD4100/ADPD4101 is a multimode sensor AFE with 8 analog inputs supporting up to 12 programmable time slots. These 12 time slots support 12 independent measurements in one sampling cycle. The 8 analog inputs can be multiplexed into one channel or two independent channels, enabling the sampling of two sensors simultaneously in a single-ended or differential configuration. The 8 LED drivers can drive up to 4 LEDs simultaneously. These LED drivers are current sinks and are independent of the LED supply voltage and LED type. The chip has two pulse voltage sources for voltage excitation. The signal path of the new AFE includes a transimpedance amplifier (TIA), a bandpass filter (BPF), an integrator (INT), and an analog-to-digital converter (ADC) stage. The digital blocks offer multiple operating modes, programmable timing, general-purpose input/output (GPIO) control, block averaging, and optional second-order to fourth-order cascaded integrator comb (CIC) filters. Data is read directly from the data register or through a first-in, first-out (FIFO) method.

This new AFE is available in two versions. One has an I ² C communication interface and the other has an SPI port. One of its advantages is that it can well support optical measurements. Its excellent automatic ambient light rejection capability is due to the use of pulses as short as 1 µ s in a synchronous modulation scheme combined with a BPF, which eliminates the need for external control loops, DC current subtraction, or digital algorithms. It uses a decimation factor higher than 1 to improve the output SNR. It has a subsampling feature that allows selected time slots to run at a lower sampling rate than the programmed sampling rate, saving power (power consumption is proportional to the sampling rate). It also has a TIA upper limit detection feature that uses a voltage comparator on the TIA output pin to set an interrupt bit when the TIA input exceeds the typical operating limit.

For peripheral blood oxygen saturation (SpO ₂ ) measurement, the new device reduces the design complexity of medical-grade SpO ₂ equipment. Built-in high-performance automatic ambient light suppression reduces the burden of mechanical and electronic design. The device's high dynamic range at low power consumption reduces the number of photodiodes or LED currents in the design to effectively determine slightly changing levels of the subject's SpO ₂ .

Figure 1: High-level block diagram of the ADPD4100 family

Biopotential is an electrical signal caused by the effects of electrochemical activity in the human body. Biopotential measurement applications include electrocardiogram (ECG) and electroencephalogram. Most of them require monitoring very low amplitude signals in frequency bands where there are many interferences. Therefore, before the signal is processed, it must be amplified and filtered. ECG biopotential measurement is widely used in vital sign monitoring, and Analog Devices provides a variety of components to accomplish this task, including the AD8233, an integrated signal conditioning module with low power consumption, suitable for portable devices, which can be combined with the ADuCM3029 (a Cortex-M3-based SoC) to create a complete system.

Bioimpedance is another measurement method that can provide useful information about the state of the body. Impedance measurements provide information about electrochemical activity, body composition, and hydration status. The measurement of each parameter requires a different measurement technique. The number of electrodes required for each measurement technique, as well as the point in time at which the technique is applied, differs depending on the frequency range used. For example, low frequencies (up to 200 Hz) are used when measuring skin impedance, while a fixed frequency of 50 kHz is often used when measuring body composition. Similarly, to measure hydration and correctly assess the amount of fluid inside and outside the cells, different frequencies are used.

Although the technology used may vary from application to application, the same single-ended AD5940 can be used to implement all bioimpedance and impedance measurements. This device provides the excitation signal and the complete impedance measurement chain, generating different frequencies to meet a variety of measurement requirements. In addition, the AD5940 can be used in conjunction with the AD8233 to create a comprehensive bioimpedance and biopotential reading system, as shown in Figure 2.

Other devices that can be used for impedance measurement include the ADuCM35x family of SoC solutions, which, in addition to a dedicated analog front end, offer a Cortex-M3 microcontroller, memory, hardware accelerators, and communication peripherals for electrochemical sensors and biosensors.

The ADP5360 combines a high performance linear charger for single lithium-ion (Li-Ion)/lithium-polymer (Li-Poly) battery charging with a programmable ultralow quiescent current fuel gauge and battery protection circuitry, an ultralow quiescent buck switching regulator, a buck-boost switching regulator, and a supervisory circuit to monitor the output voltage.

The ADP5350 is a PMIC with a buck regulator for battery charging, a programmable boost regulator for LED backlighting, a fuel gauge, and three 150 mA low dropout regulators (LDOs). This PMIC is designed for portable Li-Ion and Li-Ion polymer battery monitoring and charging. The device has a -40°C to +125°C temperature range and is available in a 32-lead (5 mm x 5 mm) LFCSP package. The ADP5350 is ideal for portable Li-Ion battery devices in consumer, medical, and instrumentation applications.

The LTC4124 is a simple, high performance wireless Li-Ion battery charger with low battery disconnect. Pin-selectable charge current (up to 100mA) and charge voltage ensure versatility while minimizing the number of external components required.

Wireless charging using the LTC4124 enables devices to be charged while sealed in a case and eliminates bulky connectors in space-constrained applications. Eliminating exposed conductive connectors also helps create more robust devices and ensures an effortless end-user experience. The LTC4124 has an NTC input for safe and temperature-appropriate charging and a battery disconnect function to prevent battery damage due to over-discharge. With a 2mm x 2mm LQFN package and a very low number of external components, it is ideal for low-power portable applications that require a small solution size.

MEMS sensors can detect gravity acceleration, so they can be used to detect activity and abnormal conditions, such as unstable gait, falls or concussions, or even monitor the posture of a subject while they are resting. In addition, MEMS sensors can also serve as a supplement to optical sensors, as the latter are susceptible to movement artifacts - when this occurs, the information provided by the accelerometer can be used to correct for it. ADXL362 is one of the popular devices in the medical field. It has a programmable measurement range of 2g to 8g and a digital output.

The ADT7422 is ADI’s first ±0.1°C accurate temperature sensor that does not require any external circuitry to operate. It can easily replace more complex and expensive solutions using alternative sensor technologies such as thermistors or RTDs. In addition, the high-precision silicon sensor (IC) is the first choice for a range of emerging applications in the medical market, such as vital sign monitoring instruments for clinical and home use. Its features are as follows:

• ±0.1°C accuracy specification enables end products to achieve temperature measurement accuracy typical of thermistors and RTDs

• No external circuitry required: smaller, lower power, and lower cost than older sensing technologies

• Fully tested and calibrated solution: no system calibration required to achieve required ±0.1°C measurement accuracy

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