What does the trigger pin do on a CMOS image sensor?
Asked 1/12/2016
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Some CMOS image sensors expose a pin labeled "trigger." What is this pin used for in a camera system? Is it related to exposure/integration time, frame timing, or synchronizing multiple cameras? For example, on sensors like the AR0330, can the trigger pin be used to synchronize frame start between sensors, and does that make the sensor behave like a global shutter?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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If we are talking about AR0330, as specified by you in the comments, what we find in that very PDF are following:
11. If the TRIGGER or OE_BAR pins or pads are not used, then they should be tied to DGNDReceives slave mode VD signal for frame rate synchronization and trigger to start a GRR frame- (page 53)
The slave mode feature of the AR0330 supports triggering the start of a frame readout from a VD signal that is supplied from an external ASIC. The slave mode signal allows for precise control of frame rate and register change updates. The VD signal is input to the trigger pin. Both the GPI_EN (R0x301A[8]) and the SLAVE_MODE (R0x30CE[4]) bits must be set to “1” to enable the slave mode.
Originally by user26160. Source · Licensed CC BY-SA 4.0
user26160
10y ago
0
Generated from our catalog & community — verify before relying on it.
On CMOS sensors, a "trigger" pin is typically a hardware timing input, not a generic exposure-control pin by itself. Based on the AR0330 documentation quoted in the community answer, that pin can be used in slave mode to receive an external VD signal that triggers the start of frame readout and supports frame-rate synchronization. In other words, yes: it can be used to synchronize frame timing between multiple cameras or to an external controller, provided the sensor and its registers are configured for that mode.
That does not automatically make the sensor a true global-shutter device. Synchronizing frame start/readout is different from exposing every pixel simultaneously. Whether the sensor behaves as rolling shutter or global reset/readout depends on the sensor’s architecture and supported modes.
So, in a camera, the trigger pin is generally used for external timing/sync control. If unused, the datasheet may require tying it to ground, as with the AR0330 example.
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