EPC635 datasheet(49/97 Pages) EPC

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6. Measurement Modes

6.1. Distance measurement modes (3D TOF)

The distance measurement modes use the on chip LED driver and the external IR-LED/LD to provide modulated light on the target. Modu -

lation control signals to the LED driver are provided by the programmable modulator (see chapter 6.1.1.).

6.1.1. Modulator

The modulator (see Figure 26) generates all signals to modulate the external IR-LED/LD via the LED driver and simultaneously all demod -

ulation signals to the pixel-field for performing a measurement. Sine and grayscale mode with all the variants are generated here.

The mode selection takes place by the modulation table registers (refer to Table 40). More details to these modes are listed in following

the chapters and in Table 32. The registers can be updated via I2C bus between the frame acquisitions. The application must take care

that the last frame's integration phase is completed before modifying these registers on the fly. This time can be detected by the applica -

tion by waiting for the falling-edge of VSYNC or the first falling-edge of HSYNC signal after SHUTTER = 1 was applied. This allows to run

continuously at the maximum frame rate. For a full-frame readout, the margin is a 3.6ms to alter these registers via I2C on the fly. This mar-

gin scales linearly with the number of row readouts.

6.1.2. Sine mode (sinusoidal modulation)

The epc635's default modulation mode is the sinusoidal modulation. After reset, all internal register values are default to operate the chip:

at 4MHz XTAL/external clock input, multiplied up to 80MHz at the PLL output, clocks the modulator with 80MHz internal mod_clk, modu-

lates LED/LD with 20MHz and acquires 4 successive DCS frames (0 ... 3) using 25.6µs integration time.

DCS2: mga 180°, mgb 0°

mod_clk

led_mod

mga

mgb

DCS3: mga 270°, mgb 90°

mod_clk

led_mod

mga

mgb

DCS0: mga 0°, mgb 180°

mod_clk

led_mod

mga

mgb

DCS1: mga 90°, mgb 270°

mod_clk

led_mod

mga

mgb

LED

= 50ns

Figure 47: Sine mode 4x DCS modulation/demodulation waveforms (mod_clk = 80MHz)

With the application of the shutter trigger pulse (HW SHUTTER = 1 or SW shutter_en = 1 via I2C), the chip performs 4 successive DCS

(Difference Correlation Sample) frame acquisitions. Each one of the 4 DCS frame types has a different phase relation between modulation

(led_mod) and demodulation (mga, mgb) signals which makes phase-to-distance calculation possible. In case of DCS0, led_mod is phase-

shifted by 0º and 180º with respect to mga and mgb, respectively. In case of DCS1, led_mod is phase-shifted by 90º and 270º. For DCS2,

the phase shifts are 180º and 0º and for DCS4, the phase shifts are 270º and 90º (see Figure 47). Note that for DCS2 and DCS3, the de-

modulation signals mga and mgb are simply swapped with respect to DCS0 and DCS1, respectively.

By programming dcs_sel = 01 (see MOD_Control register in Table 41, Modulator/demodulator registers), shutter trigger initiates 2 suc-

cessive DCS frame acquisitions (see Figure 48).

Characteristics subject to change without notice

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