Susie Maestre

user Electronics Engineer

city Innovuze Solutions Inc.

  • Heart Rate Monitor Analog Front End

  • Created: Nov 22, 2016

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Monitoring heart rate is of utmost importance nowadays especially for those that are prone to heart diseases such as hypertension. Also, heart rate monitors are usually used during exercises since heart rate is a useful indicator of the intensity of effort and body's physiological adaptation. Heart rate monitoring is an important component especially in cardiovascular fitness assessment and training programs. Polar heart rate monitors have been developed to measure healthy people’s heart rate and they target to help people exercise safely and effectively. This reference design introduces a heart rate monitor front from Analog Devices.

This reference design is an evaluation board for AD8233 low noise heart rate monitor (HRM) front end IC. This design is conveniently mounted with the necessary components for initial evaluation in fitness applications. This design is also packed with jumpers and switches that are available for setting the input bias voltage, shutdown (SDN), right leg drive shutdown (RLD SDN), fast restore (FR), and AC/DC leads off detection mode. The inputs, outputs, supply, and leads off detection are routed to test pins to simplify connectivity. The LA, RA, and RL terminals are the three electrodes connected to the hands. The RL electrode is connected to the integrated right leg drive (RLD) amplifier of the AD8233. This driven electrode functionality maintains a constant voltage between the patient and the AD8233 which greatly improves common-mode rejection ratio (CMRR). The board configures the RLD amplifier as an integrator, formed by an internal 150kΩ resistor and an external 1nF capacitor (C1). This configuration results in a loop gain of approximately 20 at line frequencies with a crossover frequency of approximately 1kHz.

This design is a good signal-conditioning block for ECG and other biopotential signal acquisition such as in electromyography (EMG). It is also very useful in fitness and activity heart rate monitors, wearable/remote health monitors, and other portable ECG. This design allows an ultralow power analog-to-digital converter (ADC) or an embedded microcontroller to easily acquire the output signal.



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