Maxim senses breathing, pulse, blood oxygen and more for wearables


Maxim bio sensing

In particular, its chips are aimed at wearables that meets US Fedral Drug Administration (FDA) sensing specifications – so far, said Maxim, no wearables have achieved FDA approval.

MAX68141 pulse heart oxymetreMAX86141 is an autonomous dual-channel (for two photodiodes) optical pulse oximeter plus heart rate sensor, measuring PPG (photoplethysmography) signals on the wrist, finger, and ear to detect heart rate, heart rate variability, and pulse oximetry.

According to Maxim healthcare v-p Sui Shieh, the chip has sufficient signal-to-noise ratio (91dB) to make accurate blood oxygen measurements at the wrist – something that defeats many detectors – fingertip measurements are the norm.

On the transmitter side, the chip has three programmable LED drivers that can be configured to drive up to six LEDs, or two linked chips can drive twelve.

On the receiver side, the optical readout channels can operate simultaneously, and each includes an analogue front-end (AFE) including a 19bit ADC, an ambient light cancellation circuit (75dB), digital noise cancellation, and a ‘picket fence event’ detection algorithm. This last item is intended to detect when the wearer is moving past repetitive light and shade in the environment – such as when walking past a fence – which might cause ambient light modulation to mimic reflective returns due to blood pulses.

Supply is 1.8V, plus 3.1-5.5V for the LEDs. Interface is SPI-compatible interface, backed by a 128-word FIFO memory.

It comes in a 2 x 1.8mm 20pin wafer-level package and operate over -40 to +85°C.

If only one channel is needed, MAX86140 has only one 19bit ADC, with associated noise cancellation.

MAX30001 ECG and BoZMAX30001 is an analogue front-end for bio-potential electrocardiogram (ECG) and bio-impedance (BioZ), measuring these on the chest or wrist to detect heart rate, respiration (BioZ) and arrhythmias – detecting anomalies sufficiently well to prompt the user to get a medical-grade multi-electrode ECG, said Shieh. It meets IEC60601 clinical ECG standards.

It also includes pacemaker edge detection, to determine if a pacemaker is in use.

“Both channels [ECG and BioZ] also have high input impedance, low noise, high CMRR [common-mode rejection], programmable gain, various low-pass and high-pass filter options, and a high resolution ADC,” said the firm. “The bio-potential channel is DC coupled, can handle large electrode voltage offsets, and has a fast recovery mode to quickly recover from overdrive conditions, such as defibrillation and electro-surgery. The bioimpedance channel includes integrated programmable current drive, works with common electrodes, and has the flexibility for 2 or 4 electrode measurements.”

This comes in a 28pin TQFN or 30bump WLP (2.7mm x 2.9mm) and operates over 0-70°C.

Evaluation kits are available for MAX86141 and ..140 (same kit) and MAX30001.



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