The PL-C720's operate with a 25 MHz input clock to the sensor. The internal clocking of the sensor is managed by the sensor’s internal PLL and in the end, the sensor provides pixels over 4 LVDS channels at an aggregate rate of 10 ns per pixel. However, there is more to consider when calculating the readout time, frame time, and frame rate:
Between each row, there is a Row Overhead Time.
Between each frame, there is a Frame Overhead Time
Readout of each image begins with the sensor reading black pixels for its Auto-Black Level corrections. These black pixels are only used internally by the sensor and are not output.
Currently, the sensor does not allow readout of an image while exposing the next.
frameTime = integrationTime + frameOverheadTime + readoutTime
integrationTime is set by the user.
frameOverheadTime is 230.64 us (t9 in the Sensor Timing Spreadsheet)
readoutTime = imageHeight/decimation * (rowTime) + NUM_BLACK_LINES * (blackRowTime)
rowTime = imageWidth/decimation * 10 ns + rowOverheadTime
NUM_BLACK_LINES = 3
blackRowTime = 1280/decimation * 10 ns + rowOverheadTime
PL-C721 = rowOverheadTime = 3 us
PL-C722 = rowOverheadTime = us
(Note, decimation can equal 1 or 2 for this Sensor. If Binning, Averaging, or Resampling are chosen, decimation = 1)
For example, full array readout (1280 x 1024, no decimation) takes
rowTime = 1280 * 10 ns + 2678.4 ns = 15.4784 us
blackRowTime = 1280 * 10 ns + 2678.4 ns = 15.4784 usreadoutTime = 1024 * (15.4784 us) + 3 * (15.4784 us) = 15.896316 ms
For example, with an 640 x 480 ROI decimated by 2 takes
rowTime = 640/2 * 10 ns + 2678.4 ns = 5.8784 us
blackRowTime = 1280/2 * 10 ns + 2678.4 ns = 9.0784 us
readoutTime = 480/2 * (5.8784 us) + 3 * (9.0784 us) = 1.4380512 ms
While the frameTime formula presented above allows us to determine the maximum frame rate the sensor will provide given the ROI, decimation, and integration time, the USB2 bus may not be capable of sustaining the bandwidth required to achieve those frame rates.