Datasheet
Photodiode Current
Or
I-V Output Pulses
Ambient Level
(Dark Level)
S
R
,
Sample RED
S
R_amb
,
Sample Ambient
(RED Phase)
S
IR
,
Sample IR
S
IR_amb
,
Sample Ambient
(IR Phase)
Plethysmograph Signal
N
N+2
N+1
N
N+1
Convert Red
Sample N
Convert Ambient
Sample N
Convert IR
Sample N
Convert Ambient
Sample N
Convert Red
Sample N+1
Convert Ambient
Sample N+1
Convert IR
Sample N+1
Convert Ambient
Sample N+1
Convert Ambient
Sample N-1
Sample phase t input current is converted to an analog voltage.
Sample phase width is variable from 0 to 25% duty cycle.
Convert Red
Sample N-1
Convert phase t sampled analog voltage is converted to a digital code.
ADC Conversion time is fixed at 25% duty cycle of PRF.
IR LED
On Signal
RED LED
On Signal
Pulse Repetition Period T = 1 / PRF
T
CONV
t
LED
LED On-Time
d 0.25 T
Rx Sample Time =
t
LED
± Settle Time
0 T
0.25 T
0.50 T
0.75 T
1.0 T
CONV
IR_amb
,
Convert Ambient Sample
(IR Phase)
CONV
R
,
Convert RED Sample
CONV
R_amb
,
Convert Ambient Sample
(RED Phase)
CONV
IR
,
Convert IR Sample
ADC Conversion
AFE4490
www.ti.com
SBAS602F –DECEMBER 2012–REVISED OCTOBER 2013
NOTE: Relationship to the AFE4490EVM is: LED1 = IR and LED2 = RED.
Figure 57. Rx Timing Diagram
Copyright © 2012–2013, Texas Instruments Incorporated Submit Documentation Feedback 27
Product Folder Links: AFE4490