Datasheet
ADPD1080/ADPD1081 Data Sheet
Rev. B | Page 46 of 74
PULSE CONNECT MODE
In pulse connect mode, the photodiode input connections are
pulsed according to the timing set up in the LED pulse timing
registers. In this mode, if the LED pulse timing is set up to provide
a 2 µs LED pulse, the device pulses the connection to the photo-
diode input for 2 µs instead of providing a 2 µs LED pulse. This
mode is an alternate to TIA ADC mode, allowing the entire
signal path, including the BPF and integrator, to measure ambient
light as well as other types of measurements with different types
of sensors (for example, electrocardiogram (ECG)).
To enable pulse connect mode, the device is configured identically
to normal mode, except that Register 0x14, Bits[3:2] = 0 for
Time Slot B, and Register 0x14, Bits[1:0] = 0 for Time Slot A.
SYNCHRONOUS ECG AND PPG MEASUREMENT
USING TIA ADC MODE
In wearable devices developed for monitoring the health care of
patients, it is often necessary to have synchronized measurements
of biomedical signals. For example, a synchronous measurement
of patient ECG and PPG can determine the pulse wave transit
time (PWTT), which can then estimate blood pressure.
The circuit shown in Figure 51 shows a synchronous ECG and
PPG measurement using the AD8233 and the ADPD1080. The
AD8233 implements a two-pole high-pass filter (HPF) with a
cutoff frequency at 0.3 Hz, and a two-pole low-pass filter (LPF)
with a cutoff frequency of 37 Hz. The output of the AD8233 is
fed to one of the current inputs of the ADPD1080 through a
200 kΩ resistor to convert the voltage output of the AD8233
into a current.
The ADPD1080 is configured to alternately measure the
photodiode signal and the ECG signal from the AD8233 on
consecutive time slots to provide fully synchronized PPG and
ECG measurements. Data can be read out of the on-chip FIFO
or straight from data registers. The ADPD1080 channel used to
process the ECG signal is set up in TIA ADC mode, and the input
bias voltage must be set to the 0.90 V setting using Bits[5:4] of
Register 0x42 if the ECG signal is on Time Slot A, or Register 0x44
on Time Slot B. The TIA gain setting can be set to optimize the
dynamic range of the signal path. The channel used to process
the PPG signal is configured in its normal operating mode.
Figure 50 shows a plot of a synchronized ECG and PPG
measurement using the AD8233 with the ADPD1080.
6000
6500
7000
7500
8000
8500
9000
9500
10000
50000
50500
51000
51500
52000
1
19
37
55
73
91
109
127
145
163
181
199
217
235
253
271
289
307
325
343
ECG (LSBs)
PPG (LSBs)
PPG
ECG
SAMPLE RATE (ms)
16110-049
Figure 50. Plot of Synchronized ECG and PPG Waveforms
RL
RA
LA
1.8V
1.8V
+IN
–IN
HPDRIVE
+V
S
HPSENSE
IAOUT
REFIN
GND
FR
AC/DC
SDN
LOD
RLD
RLDFB
OUT
OPAMP+
OPAMP–
REFOUT
SW
AD8233
6.8nF
1MΩ
1MΩ
250kΩ
2.7nF
100kΩ
180kΩ
180kΩ
1MΩ
10MΩ
10MΩ 0.1µF
10MΩ
1nF
10MΩ
10MΩ
0.1µF
360kΩ
4.7µF
TO DIGITAL
INTERFACE
4.7µF
RLD SDN
1.8V
50kΩ
PD5
PD1
PDC
LEDX1
VLED
VREF
1µF
AGND
DGND
LGND
0.1µF
0.1µF
DVDD
AVDD
1.8V
10kΩ 10kΩ
1.8V
SCL
SDA
GPIO0
GPIO1
TO DIGITAL
INTERFACE
ADPD1080
16110-048
Figure 51. Synchronized PPG and ECG Measurement Using the ADPD1080 with the AD8233
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