Version 1.0 rev 14 Aug 2019
30
Balor
4.5.2 g
lobal
s
HUtteR
Global Shutter mode, which can also be thought of as a ‘snapshot’ exposure mode, means that all pixels of the array are
exposed simultaneously. In most respects, Global Shutter can be thought of as behaving like an Interline CCD sensor.
Before the exposure begins, all pixels in the array will be held in a ‘keep clean state’, during which charge is drained
into the anti-bloom structure of each pixel. At the start of the exposure each pixel simultaneously begins to collect
charge and continues to do so for the duration of the exposure time. At the end of exposure each pixel transfers charge
simultaneously to its readout node. Importantly, Global Shutter can be configured to operate in 100% duty cycle mode
(analogous to Interline CCD), whereby an exposure can proceed as soon as the previous exposure has ended. This
results in optimal time resolution and photon collection efficiency.
Exposure Start
Exposure
Exposure End
Figure 6: An illustration of Global Shutter sensor exposure.
However, the mechanism of Global Shutter mode demands that a reference readout is performed ‘behind the scenes’, in
addition to the actual readout of charge from each pixel. Due to this additional reference readout, Global Shutter mode
carries the trade-off of reducing the maximum frame rate that would otherwise have been achieved in Rolling Shutter
mode. In addition, Global Shutter also increases the RMS read noise by a factor of ~1.4 over Rolling Shutter readout.
