An ECG measures the voltage generated by a heartbeat. The signal conditioning challenges inherent in this application are primarily due to the small signal of only 0.2 mV to 2 mV peak-to-peak, the 0.05 Hz to 150 Hz bandwidth, and the 50 Hz/60 Hz interference. Analog Devices offers a wide range of solutions to help design engineers overcome these challenges.
For signal acquisition challenges in this application, an instrumentation amplifier (in-amp) offers the ability to reject common-mode signals. The AD8220 is a JFET in-amp with low input bias current of 10 pA and high CMRR at dc and ac with RFI immunity. It operates from a single 5 V supply–ideal for a portable application. The AD8220 is available in an 8-lead MSOP.
ECG applications require a small footprint and uncompromised ADC performance at low power per conversion. The AD7980 provides 16-bit resolution, samples up to 1 MSPS, and achieves ±22 ppm INL max–all at only 7 mW power consumption. It is available in a 10-lead LFCSP.
The serial output of the AD7980 is easily isolated from the system with the ADuM240x iCoupler® digital isolator. iCoupler products, based on chip-scale microtransformer isolation, eliminate design difficulties commonly associated with optocouplers that employ LEDs and photodiodes. Typical optocoupler concerns include uncertain current transfer ratios, nonlinear transfer functions, and temperature and lifetime effects–none of which are issues for iCoupler devices that have simple digital interfaces and stable performance characteristics. The ADuM240x is compliant with IEC 60601-1 for working voltages up to 250 V rms and is available in a 16-lead SOIC wide-body package.