Vital-sign monitoring is a task that puts high demands on front ends, signal conditioning, and more. With the MAX86178 evaluation kit, Analog Devices / Maxim Integrated provides a turnkey solution that can also be used in small-series applications.

From a technical point of view, the evaluation board provides various input jacks that permit the direct connection of sensors for vital parameters. Data transmission is handled via a dedicated evaluation board processor, which Analog Devices used in various other designs in the past.

MAX86178 - An Analog Front End for The Medical Market

The core of the evaluation board at hand is Maxim Integrated’s MAX86178. This is an analog front-end chip completely dedicated to the needs of the medical industry. In particular, the specifications claim the following performance features for the PPG and ECG channels:

PPG
     Dual-Channel Optical Data-Acquisition System-
     115dB SpO2 System SNR; 112dB SNR at 16µA
ECG
     Clinical Grade ECG Acquisition System
      15.3 ENOB with 0.72μVRMS (0.05Hz to 40Hz)
      230fARMS Input-Current Noise (0.05Hz to 40Hz, +25°C)

One interesting special feature involves the chip's capability to analyze bio impedance. This capability - Maxim refers to it via the nickname BIOZ - is described as following in the datasheet:

BIOZ
     High Performance BioZ Data Acquisition System
     Low-Noise BioZ Receive Channel (17 ENOB, 0.16μVRMS)
     Sine-Wave, Square-Wave, Current and Voltage Stimulus; 16Hz to 500kHz BIA/BIS 
     Measurement with High Absolute Resistance and Reactance Accuracy

While much of the documentation for the MAX86178, such as the datasheet, is only available under NDA, the URL https://www.analog.com/en/resources/reference-designs/maxrefdes282.html provides a freely-accessible reference design. It informs the user that the communication between the microcontroller and the medical front end is handled via the SPI bus.

MAXSENSOR BLE EVKIT - A Versatile Bluetooth Communication Module

Even though the MAX86178 evaluation board has a USB port, this is used only to provide power to the system. Data communication always takes place via Bluetooth—explicitly even when the evaluation board is connected to a PC or workstation. For this, a Maxim-designed module called MAXSENSOR BLE EVKIT is used. It has an Arduino Nano-like form factor and erects a Bluetooth connection between the analog medical front end and an accompanying piece of software on the PC.

Developers who start fresh are provided with a USB Bluetooth dongle on some of the SKUs of the evaluation board. This means that work does not require the presence of Bluetooth - while most laptops have Bluetooth, Bluetooth availability on workstations remains patchy. As in the case of the stand-alone chip, the MAX86178EVKIT is also under NDA. However, the bio impedance front end is also available on the separate evaluation board called MAX30009EVKIT. Its documentation is publicly available, and much applies to this part.

Conclusion

If an embedded system needs to collect all kinds of medical information, the MAX86178 front end ensures a quick and easy design of the certification-relevant parts of the system. For small-series applications, the MAX86178EVKIT evaluation board can also be used—it provides a completely turnkey solution that is highly useful in all kinds of medical electronics applications.