SBAS704B June   2015  – October 2015 OPT8241

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Optical Characteristics
    9. 6.9 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Block
        1. 7.3.1.1 Serializer and LVDS Output Interface
        2. 7.3.1.2 Parallel CMOS Output Interface
      2. 7.3.2 Temperature Sensor
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Presence Detection for Industrial Safety
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Frequencies of Operation
          2. 8.2.1.2.2 Number of Sub-Frames and Quads
          3. 8.2.1.2.3 Field of View (FoV)
          4. 8.2.1.2.4 Lens
          5. 8.2.1.2.5 Integration Duty Cycle
          6. 8.2.1.2.6 Design Summary
        3. 8.2.1.3 Application Curve
      2. 8.2.2 People Counting and Locating
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Frequencies of Operation
          2. 8.2.2.2.2 Number of Sub-Frames and Quads
          3. 8.2.2.2.3 Field of View (FoV)
          4. 8.2.2.2.4 Lens
          5. 8.2.2.2.5 Integration Duty Cycle
          6. 8.2.2.2.6 Design Summary
        3. 8.2.2.3 Application Curve
      3. 8.2.3 People Locating and Identification
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
          1. 8.2.3.2.1 Frequencies of Operation
          2. 8.2.3.2.2 Number of Sub-Frames and Quads
          3. 8.2.3.2.3 Field of View (FoV)
          4. 8.2.3.2.4 Lens
          5. 8.2.3.2.5 Integration Duty Cycle
          6. 8.2.3.2.6 Design Summary
        3. 8.2.3.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 MIX Supply Decapacitors
      2. 10.1.2 LVDS Transmitters
      3. 10.1.3 Optical Centering
      4. 10.1.4 Image Orientation
      5. 10.1.5 Thermal Considerations
    2. 10.2 Layout Example
    3. 10.3 Mechanical Assembly Guidelines
      1. 10.3.1 Board-Level Reliability
      2. 10.3.2 Handling
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

ToF cameras provide the complete depth map of a scene. In contrast with the scanning type light detection and ranging (LIDAR) systems, the depth map of the entire scene is captured at the same instant with an array of ToF pixels. A broad classification of applications for a 3D camera include:

  • Presence detection,
  • Object location,
  • Movement detection, and
  • 3D scanning.

The OPT8241 ToF sensor, along with TI's OPT9221 ToF controller, forms a two-chip solution for creating a 3D camera. The block diagram of a complete 3D ToF camera implementation using the OPT8241 is shown in Figure 8.

OPT8241 3d_tof_camera_sbas704.gif Figure 8. 3D ToF Camera

The TI ToF estimator tool can be used to estimate the performance of a ToF camera with various configurations. The estimator allows control of the following parameters:

  • Depth resolution
  • 2D resolution (number of pixels)
  • Distance range
  • Frame rate
  • Field of view (FoV)
  • Ambient light (in watts × nm × m2 around the sensor filter bandwidth)
  • Reflectivity of the objects
For more details on how to choose the above parameters, see the white paper on the ToF system design.

8.2 Typical Applications

8.2.1 Presence Detection for Industrial Safety

Processing 3D information and a separate foreground from the background is computationally less intensive when compared to using color information from a reg, green, blue (RGB) camera. 3D information can also be used to extract the form of the object and classify the object detected as being a human, robot, vehicle, and so forth, as shown in Figure 9.

OPT8241 prsnce_detection_eg_sbas704.png Figure 9. Industrial Safety

8.2.1.1 Design Requirements

Table 3. Industrial Safety Requirements

SPECIFICATION VALUE UNITS COMMENTS
Depth resolution 7.5 Percentage of distance Temporal standard deviation of measured distance without the use of any software filters
Frame rate 30 Frames per second For reactions fast enough to trigger a machine shut down
Field of view 74.4 × 59.3 Degrees (H × V) Example only, requirements may vary
Minimum distance 1 Meters Example only, requirements may vary
Maximum distance 5 Meters Example only, requirements may vary
Minimum reflectivity of objects at which the depth resolution is specified 40 Percentage Assuming Lambertian reflection
Number of pixels 320 × 240 Rows x columns Using a full array
Ambient light 0.1 W × nm × m2 around 850 nm Low-intensity diffused sunlight
Illumination source Laser — Laser + diffuser for diffusing light uniformly through the scene

8.2.1.2 Detailed Design Procedure

Using the TI ToF estimator tool, the ToF camera design requirements can be input and the power numbers required for achieving the desired specifications can be obtained. The choice of inputs to the estimator tool is explained in the following section.

8.2.1.2.1 Frequencies of Operation

The frequencies of operation are limited by the sensor bandwidth because the illumination source is a laser. Frequencies around 75 MHz can be used to obtain a good demodulation figure of merit. Two frequencies are used to implement de-aliasing and extend the unambiguous range because frequencies around 75 MHz provide a very short unambiguous range. The two frequencies chosen for de-aliasing are 70 MHz and 80 MHz. The unambiguous range is now given by Equation 1.

Equation 1. OPT8241 uambgos_rng1_eq_sbas704.gif

For the purpose of power requirement calculations, the average frequency of 75 MHz can be used in the estimator tool.

8.2.1.2.2 Number of Sub-Frames and Quads

In this example, two sub-frames and six quads are used to obtain good dynamic range and account for wide ranges of reflectivity and distance. Also, six quads (minimum) are required for implementing de-aliasing. A depth resolution of 5% instead of the requirement of 7.5% is used as the resolution input to the estimator tool to allow for margins resulting from the additional noise when using de-aliasing.

8.2.1.2.3 Field of View (FoV)

Field of view in the horizontal direction is 74.4 degrees. The diagonal FoV can be calculated using Equation 2.

Equation 2. OPT8241 fov1_eq_sbas704.gif

The ratio of 5/4 is used to represent the ratio of the diagonal length to the horizontal length of the sensor.

8.2.1.2.4 Lens

A lens with a 1/3” image circle must be chosen. The FoV of the lens must match the requirements (that is, the FoV must be equal to 87 degrees, as calculated in Equation 2). A lower f.no is always better. For this example, use an f.no of 1.2.

8.2.1.2.5 Integration Duty Cycle

An integration duty cycle of less than 50% is chosen to keep the sensor cool in an industrial housing with no airflow. Choosing an even lower integration duty cycle can result in a marked increase in the peak illumination power. Higher peak illumination power results in a higher number of illumination elements and, thus, an increase in system cost.

8.2.1.2.6 Design Summary

A screen shot of the system estimator tool is shown in Figure 10.

OPT8241 systm_estmator_tool1_sbas704.png Figure 10. Screen Shot of the Estimator Tool

The illumination peak optical power of 1.98 W can be supplied using one high-power laser.

8.2.1.3 Application Curve

OPT8241 D014_SBAS704.gif
ρ represents object reflectivity
Figure 11. Example Industrial Safety Object Distance vs Depth Resolution

8.2.2 People Counting and Locating

Locating and tracking people is a complex problem to solve using regular RGB cameras. With the additional information of distance to each point in the scene, the algorithmic challenges become more surmountable, as shown in Figure 9.

OPT8241 grp_prsnce_detection_sbas704.png Figure 12. People Counting

8.2.2.1 Design Requirements

Table 4. People Counting Requirements

SPECIFICATION VALUE UNITS COMMENTS
Depth resolution 200 mm For basic identification of shapes
Frame rate 15 Frames per second Reasonable update rate for moderate object movement speeds
Field of view 100.0 × 83.6 Degrees (H × V) Higher FoVs are better for more coverage but are worse from a power requirement point of view
Minimum distance 1 Meters Example only, requirements may vary
Maximum distance 6 Meters Example only, requirements may vary
Typical reflectivity of objects 40 Percentage Assuming objects reflect very little infrared light and assuming Lambertian reflection.
Number of pixels 320 × 240 Rows × columns Using a full array
Ambient light 0 W × nm × m2 around 850 nm Indoor lighting conditions
Illumination source LED — LED + lens optics

8.2.2.2 Detailed Design Procedure

Using the TI ToF estimator tool, the ToF camera design requirements can be input and the power numbers required for achieving the desired specifications can be obtained by following the procedures discussed in this section.

8.2.2.2.1 Frequencies of Operation

The frequencies of operation are limited by the LED bandwidth because the source of illumination is an LED. Frequencies around 24 MHz can be used to obtain a good demodulation figure of merit if a fast-switching infrared (IR) LED is used. The unambiguous range is given by Equation 3.

Equation 3. OPT8241 uambgos_rng2_eq_sbas704.gif

8.2.2.2.2 Number of Sub-Frames and Quads

In this example, one sub-frame and four quads are used to minimize the effects of the sensor reset noise.

8.2.2.2.3 Field of View (FoV)

Field of view in the horizontal direction is 74.4 degrees. The diagonal field of view can be calculated using Equation 2.

Equation 4. OPT8241 fov2_eq_sbas704.gif

The ratio of 5/4 is used to represent the ratio of the diagonal length to the horizontal length of the sensor.

8.2.2.2.4 Lens

A lens with a 1/3” image circle must be chosen. The field of view of the lens must match the requirements (that is, the FoV must be equal to 112.3 degrees, as calculated in Equation 4 ). A lower f.no is always better. For this example, use an f.no of 1.2.

8.2.2.2.5 Integration Duty Cycle

An integration duty cycle of 60% is chosen to keep the peak illumination power requirements low. Higher peak illumination power results in a higher number of illumination elements and, thus, an increase in system cost.

8.2.2.2.6 Design Summary

A screen shot of the system estimator tool is shown in Figure 13.

OPT8241 systm_estmator_tool2_sbas704.png Figure 13. Screen Shot of the Estimator Tool

The illumination peak optical power of 2.0 W can be supplied using a single high-power LED.

8.2.2.3 Application Curve

OPT8241 D015_SBAS704.gif
ρ represents object reflectivity
Figure 14. Example People-Counting Object Distance vs Depth Resolution

8.2.3 People Locating and Identification

A skeletal structure can be used to classify identified shapes (such as humans, machines, pets, and so forth). Other possibilities include classification of people (such as children and elderly). Even identification of humans by matching the shape and movement to an existing database is possible. Such information can lend itself for use in a variety of retail solutions, home safety, security, and public and private surveillance systems, as shown in Figure 15.

OPT8241 grp_prsnce_detection_sbas704.png Figure 15. People Counting and Identification

8.2.3.1 Design Requirements

Table 5. People Counting and Identification Requirements

SPECIFICATION VALUE UNITS COMMENTS
Depth resolution 1.5 Percentage of distance To obtain skeletal structure and gait accurately and identify humans from other objects.
Frame rate 15 Frame per second Reasonable update rate for moderate object movement speeds
Field of view 100.0 x 83.6 Degrees (H X V) Higher FoVs are better for more coverage but worse from a power requirement point of view
Minimum distance 1 Meters Example only, requirements may vary
Maximum distance 6 Meters Example only, requirements may vary
Typical reflectivity of objects 40 Percentage Assuming objects reflect very little infrared light and assuming Lambertian reflection
No of pixels 320 x 240 Rows x columns Using full array
Ambient light 0 W × nm × m2 around
850 nm		 Indoor lighting conditions
Illumination source Laser — Laser + diffuser for diffusing light uniformly through the scene

8.2.3.2 Detailed Design Procedure

Using the TI ToF estimator tool, the ToF camera design requirements can be input and the power numbers required for achieving the desired specifications can be obtained. The choice of inputs to the estimator tool is explained in the following section.

8.2.3.2.1 Frequencies of Operation

The frequencies of operation are limited by the sensor bandwidth because the illumination source is a laser. Frequencies around 75 MHz can be used to obtain a good demodulation figure of merit. Two frequencies are used to implement de-aliasing and extend the unambiguous range because frequencies around 75 MHz provide a very short unambiguous range. The two frequencies chosen for de-aliasing are 70 MHz and 80 MHz. The unambiguous range is now given by Equation 5.

Equation 5. OPT8241 uambgos_rng3_eq_sbas704.gif

For the purpose of power requirement calculations, the average frequency of 75 MHz can be used in the estimator tool.

8.2.3.2.2 Number of Sub-Frames and Quads

In this example, one sub-frame and six quads are used to minimize the effects of the sensor reset noise. A depth resolution of 1% instead of the requirement of 1.5% is used as the resolution input to the estimator tool to allow for margins resulting from the additional noise when using de-aliasing.

8.2.3.2.3 Field of View (FoV)

Field of view in the horizontal direction is 74.4 degrees. The diagonal FoV can be calculated using Equation 6.

Equation 6. OPT8241 fov3_eq_sbas704.gif

The ratio of 5/4 is used to represent the ratio of the diagonal length to the horizontal length of the sensor.

8.2.3.2.4 Lens

A lens with a 1/3” image circle must be chosen. The FoV of the lens must match the requirements (that is, the FoV must be equal to 112.3 degrees, as calculated in Equation 6). A lower f.no is always better. For this example, use an f.no of 1.2.

8.2.3.2.5 Integration Duty Cycle

An integration duty cycle of 70% is chosen to keep the peak illumination power requirements low. Higher peak illumination power results in a higher number of illumination elements and, thus, an increase in system cost.

8.2.3.2.6 Design Summary

A screen shot of the system estimator tool is shown in Figure 16.

OPT8241 systm_estmator_tool3_sbas704.png Figure 16. Screen Shot of the Estimator Tool

The illumination peak optical power of 3.54 W can be supplied using two high-power lasers.

8.2.3.3 Application Curve

OPT8241 D013_SBAS704.gif
ρ represents object reflectivity
Figure 17. Example People Identification Object Distance vs Depth Resolution