ADPD4100 datasheet(40/101 Pages) AD

40 / 101 page

ADPD4100/ADPD4101

Data Sheet

Rev. 0 | Page 40 of 101

DIGITAL INTEGRATION MODE

The ADPD4100/ADPD4101 support a digital integration mode

to accommodate 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, at the expense of lower

ambient light rejection.

TIA

TIA_VREF

INx

VCx

BUF

ADC

Figure 45. 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 45. 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 are available

in the dark output data registers. Both signal and dark values

can be written to the FIFO.

The ADPD4100/ADPD4101 support one-region and two-

region digital integration 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 46. 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 47.

Table 24 shows the relevant register settings for the digital

integration 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.

PRECONDITION

LED

START OF TIME SLOT

PRECONDITION

PRE_WIDTH_x

LED_OFFSET_x

DARK1_OFFSET_x

ADC

CONVERSIONS

LIT_OFFSET_x

LED_WIDTH_x

MIN_PERIOD_x (MUST BE SET,

NOT AUTOMATICALLY CALCULATED)

NUM_INT_x

NUM_REPEAT_x

NUM_INT_x

Figure 46. One-Region Digital Integration Mode Timing Diagram

PRECONDITION

LED

START OF TIME SLOT

PRECONDITION

PRE_WIDTH_x

LED_OFFSET_x

DARK1_OFFSET_x

ADC CONVERSIONS

LIT_OFFSET_x

DARK2_OFFSET_x

LED_WIDTH_x

MIN_PERIOD_x (MUST BE SET,

NOT AUTOMATICALLY CALCULATED)

NUM_INT_x

2 × NUM_INT_x

NUM_REPEAT_x

Figure 47. Two-Region Digital Integration Mode Timing Diagram

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