SBAS883A February 2018 – June 2018 OPT3101
PRODUCTION DATA.
In this mode, the sequencer switches between two illumination driver currents to extend the dynamic range, depending on the signal saturation and lower amplitude threshold. The principle of operation is explained in Figure 18. When the illumination driver current is high and the amplitude exceeds the saturation threshold, HDR_THR_HIGH, the illumination driver is switched to the lower current. When the illumination driver current is low and the measured amplitude is below the lower threshold, HDR_THR_LOW, the illumination driver is switched to the higher current.
Figure 19 shows the frame timing diagram for HDR mode. In this mode, the first sub-frame information is used to make a decision about the validity of the output. If the first sub-frame output is valid, the same illumination DAC is used for the rest of the frame, otherwise the illumination driver is switched to the second illumination DAC current.
Amplitude thresholds for the HDR mode should be chosen according to Equation 3. Choice of the two illumination driver DAC currents depends on the end application.
HDR_THR_HIGH is the saturation threshold for the HDR switching, and should be set slightly below the actual saturation amplitude (HDR should trigger before the AFE analog path saturates). HDR_THR_LOW is the accuracy threshold, the amplitude below which the distance accuracy is poor. Figure 20 shows an illustration of the HDR operation with distance. At a distance close to the sensor, the lower illumination DAC current is used. As the object moves away from the sensor, ILLUM_DAC switches to a higher value once the amplitude falls below the lower threshold (HDR_THR_LOW). At the switching point, non-saturation is ensured by choosing the DAC currents according to Equation 3. As the object moves towards the sensor, ILLUM_DAC switches to the lower value once the amplitude reaches the saturation level (HDR_THR_HIGH). At this transition, the amplitude with ILLUM_DAC_L is above HDR_THR_LOW.
PARAMETER | ADDRESS | DESCRIPTION |
---|---|---|
EN_ADAPTIVE_HDR | 2Ah[15] | Enable adaptive HDR mode.
Minimum number of sub-frames in a frame in this mode is 2 (NUM_SUB_FRAMES = 1) |
SEL_HDR_MODE | 2Ah[16] | Chooses which current to use when EN_ADAPTIVE_HDR = 0.
0 – ILLUM_DAC_L | 1 – ILLUM_DAC_H |
HDR_THR_HIGH | 2Bh[15:0] | Saturation amplitude threshold of the auto HDR for high DAC current (ILLUM_DAC_H)
Write a value of 27000 |
HDR_THR_LOW | 2Ch[15:0] | Accuracy threshold of the auto HDR for low DAC current (ILLUM_DAC_L)
= HDR_THR_HIGH × (ILLUM_DAC_L / ILLUM_DAC_H) × (1 / 1.2) |
ILLUM_DAC_L_TX0 | 29h[4:0] | ILLUM_DAC_L of TX0 channel |
ILLUM_DAC_H_TX0 | 29h[9:5] | ILLUM_DAC_H of TX0 channel |
ILLUM_DAC_L_TX1 | 29h[14:10] | ILLUM_DAC_L of TX1 channel |
ILLUM_DAC_H_TX1 | 29h[19:15] | ILLUM_DAC_H of TX1 channel |
ILLUM_DAC_L_TX2 | 29h[23:20], 2Ah[23] | ILLUM_DAC_L of TX2 channel |
ILLUM_DAC_H_TX2 | 2Ah[22:18] | ILLUM_DAC_H of TX2 channel |