EPC635 datasheet(51/97 Pages) EPC

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The following terms are used for the formulas:

DTOF sine

Distance in meters [m]

Speed of light e.g. 300'000'000m/s

fLED

LED/LD modulation frequency e.g. 20MHz

DCS0 - DCS3

Sampling amplitude [LSB]

Phase shift caused by the time-of-flight [rad]

DOFFSET

Offset compensation [m]

In the real case of 4x DCS samples used with π-delay matching algorithm, the time of flight calculation will be:

[1]

tTOF sine

[sec ] =

π f

LED

⋅

[π + atan2(DCS2−DCS0, DCS3−DCS1)] + t

OFFSET

then, the distance calculation will be (c is the speed of light):

[2]

DTOF sine

[m] =

2 ⋅

π fLED

⋅

[π + atan2(DCS2−DCS0, DCS3−DCS1)] + D

OFFSET

2π phase wrap-around

If DTOF sine > DUnambiguity:

DTOF = DTOF sine - DUnambiguity,

if DTOF sine < DUnambiguity:

DTOF = DTOF sine + DUnambiguity,

else:

DTOF = DTOF sine

DUnambiguity

[m] =

2 ⋅

f LED

Based on the ideal case of 2x DCS samples (without any offsets), the time of flight may be computed as follows:

[3]

tTOF sine

[sec] =

π f

LED

⋅

[π + atan2(−DCS0, −DCS1)]

then, the distance calculation is:

[4]

DTOF sine

[m] =

2 ⋅

π fLED

⋅

[π + atan2(−DCS0, −DCS1)]

Sine mode: Quality of the measurement result

The epc635 provides information on the quality and the validity of the received optical signal. This reflects the confidence level of the mea -

surement result. The better the received signal, the better and more precise the distance measurement will be.

Each distance measurement of every pixel has its own validity and quality.

The primary quality indicator for the measured distance data is the peak-to-peak amplitude value of the received modulated light

ATOF sine PP. The amplitude is in direct relation ship to the distance noise: Refer to Figure 5.

After each measurement, this needs to be calculated from the DCSx values delivered by the chip. This amplitude value is the feedback pa-

rameter that is used to set the integration time for the next measurement.

[5]

ATOFsinePP =

√(DCS2−DCS0)2

(DCS3−DCS1)

Amplitude ATOF sine PP

Classification

Action

< 25 LSB

Weak illumination

Too less signal for an accurate measurement:

Increase integration time for the next measurement

25 … 100 LSB

Enough signal for a useful measurement

Distance noise approx. 4 times higher than the optimum:

No action necessary. See note below

100 … 2'000 LSB

Good signal strength

No action necessary. See note below

> 2'000 LSB

Overexposed

Decrease integration time for the next measurement.

See note below

Table 28: Signal amplitude versus classification

Note:

Generally, the higher the received signal, the better and more precise the distance measurement will be. However, it is good practice to

control the integration time such that an amplitude value between 200 ... 1'000 LSB is achieved. Higher values will only slow down the ac-

quisition rate due to longer integration times, but are not significantly improving signal to noise ratio.

Characteristics subject to change without notice

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Datasheet_epc635-V1.02

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