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.