1 Features

• Supports simultaneous and synchronized

acquisition of up to 24 PPG and a single-lead ECG

signal.

• Flexible allocation of 8 LED, 4 PD in each phase

• ECG signal chain:

– 1-lead ECG signal acquisition up to 2 kHz

– RLD output to drive a third electrode

– Input noise : 0.7 μV-rms

– Supports up to ±0.65 V differential DC offset

and +/-0.55 V common mode range

– Programmable INA gain: 11, 21

– High-pass filter with quick saturation recovery

– Integrated 300 Hz anti-aliasing low pass filter

– AC, DC lead-off detect: 2.9 nA to 92.5 nA

– Low power continuous lead-on detection

• Impedance signal chain

– Continuous low-power monitoring of impedance

between 2 electrodes

– 7 MΩ range

– 300 Ω noise on 620 kΩ

• PPG Transmitter:

– 8-Bit Programmable LED Current with range

adjustable from 25 mA to 250 mA

– Mode to fire two LEDs in parallel

– Support of 8 LEDs in Common Anode

configuration for SpO2, Multi-Wavelength HRM

• PPG Receiver:

– 2 parallel receivers (two sets of TIA/ filter)

– Supports 4 Time-Multiplexed Photodiode Inputs

to each Receiver

– 8-bit Ambient Offset subtraction at each TIA

input with 256 μA range

– 8-bit LED Offset Subtraction DAC with 64 μA

range

– Automatic ambient cancellation and dynamic

LED DC cancellation at TIA input

– Ambient rejection close to 100 dB up to 10 Hz

– Noise filtering with programmable bandwidth

– Trans-impedance Gain: 3.7 kΩ to 1 MΩ

• Accurate, Continuous Heart-Rate Monitoring:

– System SNR up to 109-dB at 16 μA PD current

– Low Current for Continuous Operation on a

Wearable Device with a Typical Value: 15-μA

for an LED, 20-μA for the Receiver

• External clock and internal oscillator modes

• Acquire data synchronized with system master

clock

• FIFO with 256-sample Depth

• SPI, I2C interfaces: Selectable by pin

• 2.6-mm × 2.5-mm DSBGA, 0.4-mm Pitch

• Supplies: Rx:1.7-1.9V (LDO Bypass); 1.9-3.6V

(LDO Enabled), Tx:3-5.5V, IO:1.7-RX_SUP

2 Applications

• Optical Heart-Rate Monitoring (HRM) for

Wearables, Hearables

• High performance ECG signal acquisition

• Synchronized PPG, ECG for BP estimation

• Heart-rate variability (HRV)

• Pulse oximetry (SpO2) measurements

3 Description

The AFE4950 device is an analog front-end (AFE)

for synchronized signal acquisition of PPG and ECG

signals. The device can also be used for optical biosensing

applications, such as heart-rate monitoring

(HRM) and saturation of peripheral capillary oxygen

(SpO2). The ECG signal chain supports 2- and 3-

electrode configurations and has an integrated Right

leg drive (RLD) buffer. The ECG signal chain can also

be used to do a continuous, low-power monitoring of

the impedance between pair of electrodes.