Good afternoon,
We are curious about the timing of the trigger with respect to the DMD refresh when in pattern mode. According to the documentation, the DMD takes 230 us to update the next bit within an image. We have the "internal trigger" and "pattern exposure" set to 693 us. We receive the trigger from the 4500 and are not sure what state the DMD is in. Is it updating or is it finished updating, or is it somewhere in between.
To determine the state of the DMD we measure the intensity of light coming from the system by integrating the response of a photodiode for x us within the 694 us period. We know that 230 us are supposed to be used up by the updating of the DMD, so we should be able to integrate for 460 us. Taking data for 3 white 3 bits followed by 1 black bit will tell us if we are integrating while the DMD is changing from white to black. We are able to change the timing of when we take an intensity measurement. We would expect, if the pattern is fully updated, the 3 white points would have the same intensity as no pixels would be black.
Now here are our results. If we integrate over the entire time we obtain a response where the first white point is low, the second is high, and the third is low. This indicates that the DMD is changing states during the integration. If we stop integrating earlier, say by 100 us, the first point is low, the second point is high, and the third point is high. This seems to indicate that the DMD is changing before the trigger. When we start integrating 100 us after the trigger, and stop integrating 100 us before the next trigger, all three points are high. So it seems that the DMD is updating while the trigger is sent.
Our analysis seems contrary to what the documentation states. However, it is not clear from the documentation what the trigger timing is when the two timings, internal trigger and pattern exposure, are set equal.
Can you please tell us when the trigger is sent with respect to the state of the DMD when the two timings are set equal? From the forums it seems that it should be either when the DMD is fully parked or before the DMD has begun to change to the next bit. Our data, however, suggests otherwise.
Thank you again for all of your help, we really appreciate it.
Justin