Teledyne Photometrics Everywhereyoulook KINETIX, Manual, Page: 20 / 41

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58-723-004 Rev A00
was increased to 3.749µsec to lower noise, the image sensor can still be read in 12ms (for a
maximum 83fps).
Of course, there are many challenges to obtaining the same analog performance from each
of the Kinetix
’s 10.2 million pixels. Whereas a CCD has a single, common output node
resulting in a uniform response. The most common problems are pixel-to-pixel non-
uniformity in gain and offset, random telegraph noise (RTN), and defective pixels with
abnormal noise or dark current characteristics (hot pixels).
Often solutions to these challenges are found in the digital domain, where Kinetix
’s
advanced real time signal processing corrects each pixel for gain and offset variation using
calibration at the factory. To address RTN and other pixel defects, real-time digital filters are
used. These corrections are described further in this manual.
Gain Combining
and Bit-Depth
As discussed in the previous sections, the column ADCs present in scientific CMOS devices
have limited dynamic range. This is addressed by making two measurements of the
accumulated charge in each pixel
– the first with very high sensitivity but limited to a
maximum signal of approximately 1000 electrons, and the second with reduced sensitivity
but capable of measuring signals up to the pixel’s 20,000 electron full well capacity.
Combining the two measurements into a single 16-bit value is the function of the digital
“gain combiner.” This mathematical operation is performed on the cameras FPGA. The
result is a single gain of approximately 0.3 e-/ADU.
In practice, the Kinetix offers both a combined ADC 16-bit output as well as 12-bit and 8-bit
single ADC output. The combined gain takes two measurements of a pixel for the combined
ADC 16-bit output. The 12-bit and 8-bit modes are able to sample 2 rows simultaneously as
only a single sample is required resulting in an increase in frame rate.
Rolling and
Global Shutter
Readout
Rolling Shutter and Global Shutter are the two primary operating modes of CMOS image
sensors. In Global Shutter readout, a global charge clearing mechanism begins the exposure
period for all pixels. Each pixel accumulates signal charge until the exposure period ends. At
this point, the accumulated charge is transferred and converted to a voltage in the pixels
output node, ending the exposure.
The strength of the Global Shutter approach is that all pixels are exposed at the same
instant in time
– an important attribute when imaging fast moving objects. The downside
of this approach is the sensor has two phases, an active image accumulation phase and a
subsequent readout phase. As the phases are not overlapped in time, the maximum
achievable frame rate is lower.