Key Features:

Analog & Mixed-Signal Front End

• 24-bit delta-sigma ADC with biopotential AFE integrated with bottom-layer exposed ENIG dry electrodes for 2-channel ECG acquisition.

• A discrete SpO₂ analog front end, Maxim MAX86141, for pulse oximetry

• The IMU tracks the patient's exact physical movement in real-time, allowing the MCU to mathematically subtract motion-induced noise from the sensitive ECG and SpO₂ signals while providing info on the user's physical state like waking, running, resting, etc.

Filtering

• High CMRR (100+) biopotential AFE to reject common mode noise

• Digital Notch filter to remove 60Hz AC hum

• Hardware LPF with common mode cut-off frequency of 19.74KHz and a differential cut-off of 9.87KHz on ECG electrodes to filter RF noise

• Digital LPF of 40 Hz cut-off frequency to remove EMG noise in ECG signals

• Active RLD (Right Leg Drive) and low PGA (To prevent saturation) to remove dry electrode DC offset and Common mode noise from ECG

Power Management

• A high-end PMIC specifically designed for wearables - Maxim MAX77654 SIMO PMIC

• Specifications of PMIC are a 1S LiPo BMS and charger, 2 buck rails, 1 boost rail and 1 ultra-low noise LDO

• Buck-LDO cascade for biopotential AFE for stable and low noise power rail

PCB Design

• Targeting 30mm * 30 mm 6-layer high-density PCB

• Using packages like BGA, VGA, QFN, etc. as much as possible for space efficiency.

• Using small sizes like 0201 for passives

• Stackup target - At least two internal GND planes, GND pours on rest of the layers, one power plane and three SIG layers

• Noise reduction techniques such as via shielding, proper return path tracking and physical isolation of Analog/Digital/Power/RF sections