With the development of the times, mobile phones have more and more functions, not only can take beautiful photos, play audio and video streaming files, but also access a variety of services - and now gradually become personal trainers. When equipped with sensors or connected to wearable sensors, these devices can be used to monitor people's daily activities and personal health. Driven by increasing health awareness, people are beginning to focus on measuring vital signs such as heart rate, body temperature, oxygen saturation, blood pressure, activity levels (calorie) and calorie burns—and tracking daily trends in these parameters.
A universal sensor front end with multiple sensors can now monitor these parameters. The bigger challenge is to minimize size and extend battery life. This article will discuss solutions for the rapidly growing market for wearable electronics.
Most important vital signs
Pulse or heart rate is one of the most important parameters to monitor. In addition to the number of beats per minute, you should also check the relationship between cardiac behavior and activity. Heart rhythm is also very important because the rapidly changing heart rate is a sign of heart disease.
Monitoring of heart rate and cardiac activity is usually achieved by measuring electrophysiological signals using an electrocardiogram (ECG). Electrodes connected to the body measure the signal generated by the electrical activity of the heart tissue. The professional diagnostic system is based on this principle, which can connect up to 10 electrodes in the chest and limbs. The ECG provides detailed information about the different components of the heartbeat (P wave, QRS and T waves).
The use of single-lead ECGs in the sports world is becoming more common, using a two-electrode chest strap to measure cardiac activity. Although various ECG waveforms can be detected, most systems only measure heart rate. These chest straps are not comfortable to wear. As a result, the sports and healthcare industries are looking for alternatives, such as integrating electrodes into sweatshirts. The AD8232 single-lead heart rate monitor front end (Figure 1) was developed specifically for such low-power wearable applications. The device incorporates an instrumentation amplifier with a gain of 100V/V and a high-pass filter that blocks the offset voltage generated by the half-cell potential of the electrodes on the skin. The output buffer and low-pass filter suppress high-frequency components (EMG signals) generated by muscle activity. This low-power front-end consumes 170μA and can be used with the 16-bit on-chip meter ADuCM350 for high-performance, single-lead ECG measurements.
Figure 1: The AD8232 single-lead ECG front end.
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