Fermion TMF8801 ToF Distance Ranging Sensor (20-2500mm) - Datasheet

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TMF8801
Application Information
Datasheet PUBLIC
DS000648 v8-00 • 2021-Jul-08
69 57
9.2 Reference SPAD, TDC and Histogram
There is an internal reference SPAD with associated TDC and histogram. This is used to determine
the start time of each pulse. The reference SPAD is processed during calibration. The reference
channel processing occurs internal to the device with no user interaction required.
All histograms can be processed inside the TMF8801 and/or readout through the I²C interface. As the
readout is constrained by the I²C speed and the I²C bus utilization (TMF8801 can support I²C speed
up to 1 MHz), it is recommended to readout the histograms only for debugging purposes.
Figure 114 shows a histogram obtained from TMF8801. The x-axis is scaled in bins, where the
nominal bin size is 100 ps per bin and each TDC has 256 bins. The y-axis is scaled in counts
represented by 16-bit values. The green line shows the reference histogram from TDC0 and its peak
marks the reference or zero distance. The other four lines (blue, cyan, red and violet) are the
histograms obtained from TDC1 to TDC4. A target at 20 cm is used to generate the peak around
bin 25.
Figure 114:
Histogram
(1) The above histogram is used for general device information only. The actual histogram differ due to different bin size
and modes used.