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MT9P401 Arkusz danych(PDF) 33 Page - ON Semiconductor |
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MT9P401 Arkusz danych(HTML) 33 Page - ON Semiconductor |
33 / 45 page MT9P401 CONFIDENTIAL AND PROPRIETARY NOT FOR PUBLIC RELEASE www.onsemi.com 33 scans. Each row is exposed for the same duration, but at slightly different point in time, which can cause a shear in moving subjects. Whenever the mode is changed to an ERS mode (even from another ERS mode), and before the first frame following reset, there is an anti−blooming sequence where all rows are placed in reset. This sequence must complete before continuous readout begins. This delay is: tALLRESET = 16 × 2004 × tACLK Global Reset Release The GRR modes attempt to address the shearing effect by starting all rows’ exposures at the same time. Instead of the first scan used in ERS mode, the reset to each row is released simultaneously. The second scan occurs as normal, so the exposure time for each row would different. Typically, an external mechanical shutter would be used to stop the exposure of all rows simultaneously. In GRR modes, there is a startup overhead before each frame as all rows are initially placed in the reset state (tALLRESET). Unlike ERS mode, this delay always occurs before each frame. However, it occurs as soon as possible after the preceding frame, so typically the time from trigger to the start of exposure does not include this delay. To ensure that this is the case, the first trigger must occur no sooner than tALLRESET after the previous frame is read out. Exposure The nominal exposure time, tEXP, is the effective shutter time in ERS modes, and is defined by the shutter width, SW, and the shutter overhead, SO, which includes the effect of Shutter_Delay. Exposure time for other modes is defined relative to this time. Increasing Shutter_Delay (SD) decreases the exposure time. Exposure times are typically specified in units of row time, although it is possible to fine−tune exposures in units of tACLKs (where tACLK is 2 × tPIXCLK). tEXP = SW × tROW – SO × 2 × tPIXCLK where: SW = max(1, (2 × 16 × Shutter_Width_Upper) + Shutter_Width_Lower) SO = 208 × (Row_Bin + 1) + 98 + min(SD, SDmax) – 94 SD = Shutter_Delay + 1 SDmax = 1232; if SW < 3 1504, otherwise The exposure time is calculated by determining the reset time of each pixel row (with time 0 being the start of the first row time), and subtracting it from the sample time. Under normal conditions in ERS modes, every pixel should end up with the same exposure time. In global shutter release modes, or in row binning modes, the exposure times of individual pixels can vary. In global shutter release modes (described later) exposure time starts simultaneously for all rows, but still ends as defined above. In a real system, the exposure would be stopped by a mechanical shutter, which would effectively stop the exposure to all rows simultaneously. Because this specification does not consider the effect of an external shutter, each output row’s exposure time will differ by tROW from the previous row. Global shutter modes also introduce a constant added to the shutter time for each row, because the exposure starts during the global shutter sequence, and not during any row’s shutter sequence. For each additional row in a row bin, this offset will increase by the length of the shutter sequence. In Bulb_Exposure modes (also detailed later), the exposure time is determined by the width of the TRIGGER pulse rather than the shutter width registers. In ERS bulb mode, it is still a multiple of row times, and the shutter overhead equation still applies. In GRR bulb mode, the exposure time is granular to ACLKs, and shutter overhead (and thus Shutter_Delay) has no effect. Operating Modes In the default operating mode, the MT9P401 continuously samples and outputs frames. It can be put in “snapshot” or triggered mode by setting snapshot, which means that it samples and outputs a frame only when triggered. To leave snapshot mode, it is necessary to first clear Snapshot then issue a restart. When in snapshot mode, the sensor can use the ERS or the GRR. The exposure can be controlled as normal, with the Shutter_Width_Lower and Shutter_Width_Upper registers, or it can be controlled using the external TRIGGER signal. The various operating modes are summarized in Table 15. Table 15. OPERATING MODE Mode Settings Description ERS Continuous Default Frames are output continuously at the frame rate defined by tFRAME. ERS is used, and the exposure time is electronically controlled to be tEXP ERS Snapshot Snapshot = 1 Frames are output one at a time, with each frame initiated by a trigger. ERS is used, and the exposure time is electronically controlled to be tEXP ERS Bulb Snapshot = 1; Bulb_Exposure = 1 Frames are output one at a time, with each frame’s exposure initiated by a trigger. ERS is used. End of exposure and readout are initiated by a second trigger GRR Snapshot Snapshot = 1; Global_Reset = 1 Frames are output one at a time, with each frame initiated by a trigger. GRR is used. Readout is electronically triggered based on SW GRR Bulb Snapshot = 1; Bulb_Exposure = 1; Global_Reset = 1 Frames are output one at a time, with each frame initiated by a trigger. GRR is used. Readout is initiated by a second trigger 1. In ERS bulb mode, SW must be greater than 4 (use trigger wider than tROW x 4). |
Podobny numer części - MT9P401_17 |
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Podobny opis - MT9P401_17 |
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