ADPD4200 datasheet(36/93 Pages) AD

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Data Sheet

ADPD4200

APPLICATIONS INFORMATION

analog.com

Rev. 0 | 36 of 93

DIGITAL INTEGRATION MODE

The ADPD4200 supports a digital integration mode to accommo-

date sensors that require longer pulses than can be supported

in the typical analog integration modes. Digital integration mode

allows the system to use a larger LED duty cycle than the analog

integration modes, which may result in the highest achievable

levels of SNR.

Figure 33. Signal Path for Digital Integration Mode

In digital integration mode, the BPF is bypassed and the integrator

is configured as a buffer, resulting in the signal path shown in

Figure 33. Digital integration regions are configured by the user

and separated into lit and dark regions. The LED is pulsed in the

lit region, and the LED is off in the dark region. ADC samples are

taken at 1 μs intervals within the lit and dark regions and are then

digitally integrated. The integration of the ADC samples from the

dark region is subtracted from the integration of the ADC samples

from the lit region and the result is written into the relevant signal

output data registers. The sum of the samples from just the dark

region is available in the dark output data registers. Both signal and

dark values can be written to the FIFO.

The ADPD4200 support one-region and two-region digital integra-

tion modes. In one-region digital integration mode, an equal number

of dark and lit samples are taken where all of the dark samples are

taken in the dark region just prior to the lit region. One-region digital

integration mode is illustrated in the timing diagram in

Figure 34. In two-region digital integration mode, an equal number

of dark and lit samples are taken. However, the dark region is split

such that half of the samples are taken in the dark region prior to

the lit region, and the other half is taken in the dark region following

the lit region. The two-region digital integration mode results in

higher ambient light rejection than the one-region digital integration

mode in situations with a varying ambient light level. A timing

diagram for two-region digital integration mode is shown in

Figure 35.

Table 22 shows the relevant register settings for the digital integra-

tion modes of operation. Note that only a single channel can be

used in digital integration mode. Two channels are not supported

for digital integration mode of operation. The MIN_PERIOD_x bits

must also be manually set with the correct period because the

minimum period is not automatically calculated in digital integration

mode.

Figure 34. One-Region Digital Integration Mode Timing Diagram

Figure 35. Two-Region Digital Integration Mode Timing Diagram

ADPD4200 Datasheet(PDF) 36 Page - Analog Devices

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