1 Features

1• Synchronized PPG, ECG signal acquisition at

data rates up to 1 kHz

• ECG signal chain:

– Standalone ECG acquisition up to 4 kHz

– Input bias: 1-lead ECG with RLD bias

– Programmable INA gain: 2.15 to 12.92

– Input noise (1 Hz to 150 Hz): 2.5 μVrms at

1 kHz, 1.25 μVrms at 4-kHz data rate

– AC, DC lead-off detect: 12.5-nA to 100-nA

– IEC 60601 Test report available on request

• PPG receiver:

– Supports three time-multiplexed PD inputs

– 24-Bit representation of current from PD

– DC offset subtraction DAC (Up to ±126-μA) at

TIA input for each LED, ambient

– Digital ambient subtraction at ADC output

– Noise filtering with programmable bandwidth

– Transimpedance gain: 10 kΩ to 2 MΩ

– Dynamic range up to 100 dB

– Receiver operates in PPG-only mode at

approximately 1-μA/Hz sampling rate

– Power-down mode: approximately 0 μA

• PPG transmitter:

– Four LEDs in common anode configuration

– 8-Bit LED current up to 200 mA

– Mode to fire two LEDs in parallel

– Programmable LED on-time

– Simultaneous support of three LEDs for SpO2,

or multiwavelength HRM

– Average current of 30 μA adequate for a

typical heart-rate monitoring scenario:

– 20-mA Setting, 60-μs pulse duration,

25-Hz sampling rate

• Clocking using an external or internal clock

• FIFO with 128-sample depth for ECG and PPG

• I2C, SPI interfaces: selectable by pin

• 2.6-mm × 2.1-mm, 0.4-mm Pitch DSBGA package

• Supplies:

– Rx: 1.8 V to 1.9 V (LDO bypass),

2.0 V to 3.6 V (LDO enabled)

– Tx: 3 V to 5.25 V

– IO: 1.7 V to Rx_SUP

2 Applications

• Synchronized PPG, ECG for blood pressure

estimation

• HRM for wearables, hearables

• Heart-rate variability (HRV)

• Pulse oximetry (SpO2) measurements

3 Description

The AFE4900 device is an analog front-end (AFE) for

synchronized electrocardiogram (ECG),

photoplethysmogram (PPG) signal acquisition. The

device can also be used for optical bio-sensing

applications, such as heart-rate monitoring (HRM)

and saturation of peripheral capillary oxygen (SpO2).

The PPG signal chain supports up to four switching

light-emitting diodes (LEDs) and up to three

photodiodes (PDs). The LEDs can be switched on

using a fully integrated LED driver. The current from

the photodiode is converted into voltage by the

transimpedance amplifier (TIA) and digitized using an

analog-to-digital converter (ADC). The ECG signal

chain has an instrumentation amplifier (INA) with a

programmable gain that interfaces to the same ADC.

A right-leg drive (RLD) amplifier set can be used to

the bias for the ECG input pins. AC and dc lead-off

detect schemes are supported. The ADC codes from

the PPG and ECG phases can be stored in a 128-

sample first in, first out (FIFO) block and read out

using either an I2C or a serial programming interface

(SPI) interface.