Rolling Shutter vs. Global Shutter0 pages

TECHNICAL NOTE

Rolling Shutter vs. Global Shutter

Preamplier

Serial Register

A/D

Pixels

Output
Node
Single Digitization
Point is Rate
Limiting Step

Pixels

Figure 1. Basic schematics of
CCD (above) and CMOS (left)
sensor architectures.

CDS

CDS

CDS

CDS

A/D

A/D

A/D

A/D

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CCD and CMOS
Sensor Architecture
and Readout Modes
Two image sensor types widely used in cameras for microscopy
are scientific grade Charge Coupled Devices (CCD) and scientific
Complementary Metal Oxide Semiconductors (CMOS or sCMOS).
There is a number of similarities between the two technologies,
but one major distinction is the way each sensor reads the signal
accumulated at a given pixel. This Tech Note will explain how
the differences in readout modes impact the exposure timing,
illumination, and triggering of cameras and light sources in
microscopy experiments.
While many readout modes exist, CCD cameras popular in
microscopy often use interline transfer CCDs in a Global
Shutter mode. In Global Shutter mode, every pixel is exposed
simultaneously at the same instant in time. This is particularly
beneficial when the image is changing from frame to frame. The
CCD however has an inherent disadvantage when it comes to
frame rate. When the exposure is complete, the signal from each
pixel is serially transferred to a single Analog-to-Digital Converter
(A/D). The CCD’s ultimate frame rate is limited by the rate that
individual pixels can be transferred and then digitized. The more
pixels to transfer in a sensor, the slower the total frame rate of
the camera.
A CMOS chip eliminates this bottleneck by using an A/D for every
column of pixels, which can number in the thousands. The total
number of pixels digitized by any one converter is significantly
reduced, enabling shorter readout times and consequently faster
frame rates. While there are many parallel A/D’s sharing the
workload, the entire sensor array must still be converted one
row at a time. This results in a small time delay between each
row’s readout.

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