Integrated Optical Module with Ambient
Light Rejection and Three LEDs
Data Sheet
Rev. SpA Document Feedback
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FEATURES
2.8 mm × 6.5 mm module with integrated optical components
2 green LEDs located on either side of the photodiode,
1 infrared LED, and 1 photodiode
True 3-channel 250 mA LED driver
Separate LED and AFE settings for each channel
Dual data registers for each LED return signal
14-bit ADC
20-bit burst accumulator enabling 20 bits per sample period
On-board sample to sample accumulator enabling up to
27 bits per data read
Custom optical package made to work under a glass window
Optimized SNR for signal limited cases
APPLICATIONS
Optical heart rate monitoring
Reflective SpO
2
measurement
GENERAL DESCRIPTION
The ADPD174GGI is a complete photometric system designed to
measure optical signals from ambient light and from synchronous
reflected LED pulses. Synchronous measurement offers best-in-
class rejection of ambient light interference, both dc and ac. The
module integrates a highly efficient photometric front end, three
LEDs, and a photodiode (PD). All of these items are housed in a
custom package that prevents light from going directly from the
LED to the photodiode without first entering the subject.
The front end of the ASIC consists of a control block, a 14-bit
analog-to-digital converter (ADC) with a 20-bit burst accumula-
tor, and three flexible, independently configurable LED drivers.
The control circuitry includes flexible LED signaling and synchro-
nous detection. The analog front end (AFE) features best-in-class
rejection of signal offset and corruption due to modulated
interference commonly caused by ambient light. The data
output and functional configuration occur over a 1.8 V I
2
C
interface.
FUNCTIONAL BLOCK DIAGRAM
Figure 1.
For more information about the ADPD174GGI, contact Analog Devices, Inc., at optical_sensors@analog.com.
ANALOG BLOCK
TIME SLOT A
TIME SLOT B
DIGITAL
INTERFACE
AND
CONTROL
AFE CONFIGURATION,
TIME SLOT A
AFE CONFIGURATION,
TIME SLOT B
SDA
SCL
INT
DGND
AGND
VREF
1µF
VDD1
VDD2
ADPD174GGI
14-BIT
ADC
IR
LED3 DRIVER
LED2 DRIVER
LED3 LEVEL AND TIMING CONTROL
LED2 LEVEL AND TIMING CONTROL
LED1 DRIVER
LED1 LEVEL AND TIMING CONTROL
LGND
VLED2
VLED1
LED3/DNC
LED2
LED1/DNC
GREEN
LEDs
AFE: SIGNAL CONDITIONING
TIA
V
BIAS
AMBIENT
LIGHT
REJECTION
AFE
GAIN
13519-001
NOTES
1. DNC = DO NOT CONNECT. DO NOT CONNECT TO THIS PIN WHEN USING INTERNAL LEDs.
PHOTODIODE
CH. 1
DATA
DATA
