TI AFE4420YZR

The AFE4420 is an analog front-end (AFE) designed for optical biosensing applications, such as heart rate monitoring (HRM) and blood oxygen saturation (SpO2) measurement. This device supports up to four switchable light-emitting diodes (LEDs) and four photodiodes. Up to 16 signal phases can be defined, and signals can be acquired from each phase in a synchronous manner and stored in a 128-sample first-in, first-out (FIFO) block. The FIFO can be read via the I2C or SPI interface. This AFE is also equipped with a fully integrated LED driver with 8-bit current control. The device features wide dynamic range transmit and receive circuits, which help detect ultra-small signal levels.

• Up to 16-phase signal acquisition with flexible LED and PD assignment within each phase
• Accurate, continuous heart rate monitoring with up to 100dB dynamic range
• Low-current continuous operation on wearables — typical values: 15μA for LED, 20μA for receiver
• Common-anode LED configuration support
• 8-bit programmable LED current, adjustable from 50mA to 200mA
• Parallel dual-LED illumination mode
• Programmable LED on-time
• Simultaneous support for 4 LEDs — optimized for SpO2, HRM, or multi-wavelength HRM
• Programmable control signals for up to 8 LEDs using external SPDT switches
• 4-channel time-division multiplexed photodiode input support
• Independent DC offset cancellation DAC at TIA input — per LED and ambient light phase, 7-bit control with range up to ±254μA
• Transimpedance gain: 10kΩ to 2MΩ
• Digital ambient cancellation at ADC output for ambient noise suppression
• Noise filter with programmable bandwidth
• External clock and internal oscillator mode support
• Auto Ambient Cancellation Mode (AACM) for increased receiver dynamic range
• Two programmable GPIO pins with flexible interrupt generation
• FIFO with 128-sample depth
• I²C and SPI interface — pin-selectable
• Operating temperature range: -40℃ to +85℃
• 2.6mm × 2.1mm DSBGA package, 0.4mm pitch
• Rx: 1.7V to 1.9V (LDO bypass), 1.9V to 3.6V (LDO enabled)
• Tx: 3V to 5.5V
• IO: 1.7V to RX_SUP

• Optical heart rate monitoring (HRM) for wearables and ear-worn devices
• Heart rate variability (HRV) analysis
• Pulse oximetry (SpO2) measurement
• Maximum oxygen uptake (VO2 Max)
• Calorie expenditure