Healthcare ICs
Volume 9, Issue 8 YOUR SEMICONDUCTOR SOLUTIONS RESOURCE

Tightly Integrated, Low Cost Solutions for Heart Rate Monitors Increase Accuracy and Reliability

A heart rate monitor may be part of a complete health monitoring platform, including activity sensing, body fat analysis, and temperature monitoring, or a standalone consumer grade device worn on the body or integrated into a piece of exercise equipment. Those worn on the body must operate off a coin cell battery. Regardless of the end product, the heart rate monitor must function well under harsh environments where environmental, electrophysiological, magnetic, and electronic noise can affect the accuracy and reliability of signal measurement. All electronics required for signal processing and display must fit typically within one square inch or less, and the design must be highly cost efficient. Any system communication must be compliant with industry standards (USB or low power Bluetooth).

Solution
ADI offers low power precision amplifier and converter technologies for cost-sensitive heart rate monitoring devices used for health and wellness programs. These devices accommodate various electrodes and body sensors and meet low power, small size, and high accuracy requirements. ADI amplifiers and converters integrate tightly with additional technologies and functionality including MEMS accelerometers, RF transceivers, touch control interface sensors, and temp sensors, enabling flexible front-end electronic design that will support various HRM applications.

Smaller than the tip of a pencil, the AD8235 instrumentation amplifier draws only 40 µA (max) of supply current, yet features 6 nA shutdown current and 1 pA input bias current. It is ideally suited for power efficient, portable, lightweight medical devices, and consumer health products, including heart rate monitors and activity monitors where a small size and long battery life are critical. The AD8235 is available in a 1.6 mm × 2.0 mm WLCSP package. Pricing: $1.59.

The AD7798 ADC is a low power, complete analog front end that contains a low noise, 16-bit Σ-Δ ADC with three differential analog inputs. The on-chip, low noise instrumentation amplifier means that signals of small amplitude can be interfaced directly to the ADC. On-chip features include a low-side power switch, reference detect, programmable digital output pins, burnout currents, and an internal clock oscillator. The part operates with a power supply from 2.7 V to 5.25 V and consumes a current of 300 µA typical. It is available in a 16-lead TSSOP package. Pricing: $3.85.

The AD8619 quad micropower op amp is a cost efficient option for HRM designs particularly when combined with the AD8235 in-amp and AD7798 ADC. The AD8619 is fully specified to operate from 1.8 V to 5.0 V single supply and combines 22 nV/√Hz noise, 1 pA max input bias current, and draws 38 µA of supply current. It is available in 14-lead TSSOP and 14-lead SOIC packages. Pricing: $1.11.

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Heart Rate Monitors

Complementary Components:

  • ADR36x and ADR42x families of low power voltage references. Pricing: starting at $0.78.
  • ADXL345: 3-axis, ultralow power accelerometer with high resolution measurement at up to ±16 g. Pricing: $3.04.
  • ADF7023: low power transceiver. Pricing: $2.88.

Continua Health AllianceADI is a member of Continua Health Alliance, a coalition of technology, medical devices, and health and fitness leaders dedicated to enabling interoperable healthcare products and solutions worldwide. www.continuaalliance.org.

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