TMD2621 datasheet(9/59 Pages) OSRAM

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[v4-00] 2023-Apr-12

TMD2621 − Detailed Description

Proximity

The proximity system consists of an IR VCSEL and its driver

generating periodic IR pulses which are reflected and received

by the proximity photodiode and modulator sub-system. The

reflected energy is measured by integrating the photodiode

current and translating it to an ADC input voltage. The presence

of a reflective object at some distance can be extracted as a

function of ADC output data which represents the reflected

signal intensity.

Proximity results are affected by three fundamental factors: the

integrated IR VCSEL emission, IR reception (signal + crosstalk),

and environmental factors, including target distance and

surface reflectivity. The IR reception signal path begins with IR

detection from a photodiode and ends with the 14-bit

proximity result in PDATA register. Signal from the photodiode

is amplified, and offset adjusted to optimize performance.

Offset correction or crosstalk compensation is accomplished by

adjustment to the POFFSET register. The analog circuitry of the

device applies the offset value as a subtraction to the signal

accumulation, therefore a positive offset value has the effect of

decreasing the PDATA value. The integrated offset calibration

feature performs this crosstalk compensation.

The proximity IR VCSEL emission is designed to be able to

synchronize to the display VSYNC signal with a delay time

defined by PSD when PVSYNC_EN=1. PTIME defines the

duration of one proximity sample. PTIME needs to be

programmed to a value greater than the sample integration

time, otherwise it will be ignored. Using PTIME, proximity

sample timing can be programmed to skip VSYNC periods. The

device hardware allows to collect and average multiple

proximity samples for a single proximity measurement result

by programming the PROX_DATA_AVG register. Device

temperature is measured and updated in the TDATA register

after every proximity measurement cycle when TEN=1 and

ENAB_TEMP_SENSOR =1. PWTIME provides the ability to add

wait time and defines the repetition period of one proximity

measurement cycle. The subsequent proximity cycle will occur

on the first VSYNC after the end of the PWTIME period, plus the

delay defined by PSD.

Figure 10 shows an example of proximity integration and data

sampling for the TMD2621.

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