Small, Low Power, Single-Lead Analog Front End for Vital Sign Monitoring Applications

In contrast to similar offerings, which are often derived from existing clinical cardiac monitor solutions, the AD8232 AFE was designed specifically to meet the ECG signal conditioning requirements of emerging fitness, portable/wearable monitoring and remote health monitoring equipment. Unlike the topologies employed in many of today’s integrated solutions, the highly flexible analog filtering configuration of the AD8232 incorporates a two-pole, high-pass filter that is tightly coupled with the IC’s instrumentation amplifier architecture, and an uncommitted operational (gain) amplifier that enables the user to employ multi-pole low pass filtering techniques to remove line noise and other interference.

By performing large-gain and high-pass signal conditioning in a single stage in the analog domain, the AD8232 can accommodate electrode DC offsets while operating on a single supply voltage without sacrificing performance or signal quality. With an analog output, the AD8232 can be paired with either a discrete A/D converter or a microcontroller with an embedded A/D converter, which provides system designers with the flexibility to deliver a new level of value and performance for fitness and healthcare monitoring.

“There is a growing demand for fixed, portable, and even wearable heart-rate monitors that provide vital sign measurements for athletes in training, home fitness equipment or remote health monitoring,” said Patrick O’Doherty, vice president, Healthcare Segment, Analog Devices. “This level of non-diagnostic monitoring is subject to a unique set of design considerations, and ADI believes the AD8232 offers manufacturers a better partitioned, more balanced signal processing architecture with greater flexibility in terms of back-end component selection and filter design. This will translate into system designs that are easier to design, more reliable and more accurate than existing solutions.”

In addition to the instrumentation and gain amplifier, the AD8232 heart-rate monitor AFE incorporates a reference buffer, right leg drive circuit and shutdown function. The AD8232 also includes user-selectable (AC or DC) leads-off detect circuitry that monitors when an electrode is disconnected from the patient or user, providing an alert to the system. This new heart-rate monitor AFE offers an innovative fast-restore mode that quickly and automatically recovers the cardiac signal in the event a user temporarily loses contact with an electrode during exercise, or other activity, greatly improving the quality of the end-user experience.

AD8232 Heart Rate Monitor Key Features:
• Supply current: 180 µA
• 4-mm x 4-mm, 20-pin LFCSP package
• 2-pole adjustable high-pass filter
• 3-pole adjustable low-pass filter and gain amplifier
• AC/DC Leads-off detection and fast-restore mode
• Noise: 20-µVp-p (0.5 Hz to 40 Hz)
• Common-mode rejection ratio: 80 dB (DC to 60 Hz)
• Integrated Right Leg Drive
• 2.0 to 3.5V supply voltage range
• Shutdown function

The AD8232 is sampling now with full production scheduled for August 2012, priced at 1.36 USD per unit in 1,000 quantities. The AD8232 is available in a 4mm x 4mm, 20-pin, LFCSP package.