The past decade has seen tremendous progress in mobile phones, wearables, and digital health. In particular, with the continuous development of electronic technology and new breakthroughs in technologies such as cloud computing, artificial intelligence (AI), the Internet of Things (IoT), and 5G, digital health has expanded and been adopted rapidly. Some vital signs monitoring (VSM) functions have been built into mobile phones, watches, and other smart wearable devices, making them available to a wider range of people. People’s growing awareness of health has triggered the demand for small but highly accurate devices that can measure various vital signs and health indicators such as body temperature, heart rate, respiratory rate, blood oxygen saturation (SpO2), blood pressure, and body composition. The COVID-19 pandemic has led to a surge in demand for multi-parameter vital signs (including body temperature, SpO2, and heart rate) monitoring devices for hospitals and homes. The demand for small and convenient health tracking devices, preferably smart wearables, has reached a new high.
Adding multiple sensing functions to such a small device is challenging because it requires a smaller form factor, lower power consumption, and significantly improved performance of multi-parameter functions. However, these challenges can now be met with a single analog front end (AFE) solution. This new AFE can be used as a multi-parameter vital signs monitoring center, supporting simultaneous measurements. Its low noise, high signal-to-noise ratio (SNR), small size, and low power consumption can significantly improve medical devices, especially wearable technology. For doctors, patients, and consumers, it makes vital signs monitoring easier than before and provides higher performance, longer battery life, and higher accuracy without the annoyance and discomfort caused by multiple devices. This article discusses some of the breakthrough functions and features of this single analog front-end solution.
Overview of the New Analog Front-End
ADPD4100/ADPD4101 is a multimode sensor AFE with 8 analog inputs and supports up to 12 programmable time slots. These 12 time slots support 12 independent measurements in one sampling cycle. The 8 analog inputs are multiplexed into one channel or two independent channels, which can sample two sensors simultaneously in single-ended or differential configurations. 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 transimpedance amplifier (TIA), bandpass filter (BPF), integrator (INT), and analog-to-digital converter (ADC) stages. The digital blocks offer multiple operating modes, programmable timing, general-purpose input/output (GPIO) control, block averaging, and selectable 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.
There are two versions of this new AFE. One has an I2C communication interface and the other has an SPI port. One of the advantages of the ADPD4100/ADPD4101 is related to optical measurement. Its excellent automatic ambient light rejection capability is due to the use of pulses as short as 1 µs in a synchronous modulation scheme combined with a BPF, which eliminates the need for external control loops, dc current subtraction, or digital algorithms. A decimation factor higher than 1 is used 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 limits.
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 SpO2 measurement. The multiple operating modes of this new multi-parameter VSM AFE can accommodate 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.
Post time: Jul-04-2025