TC246 Datasheet, PDF (6/30 Pages) Texas Instruments – 680 x 500 PIXEL IMPACTRON™ COLOR CCD IMAGE SENSOR

TC246
SOCS096 – JULY 2010
www.ti.com
DETAILED DESCRIPTION
The TC246 consists of five basic functional blocks: The image-sensing area, the image-storage area, the serial
register, the charge multiplier, and the charge detection node with buffer amplifier. The location of each of these
blocks is identified in the functional block diagram.
Image Sensing and Storage areas
As light enters the silicon in the image-sensing area, electrons are generated and collected in potential wells of
the pixels. Color is accomplished by on-chip color mosaic filter. (see the sensor topology diagram for a mapping
of the color filter) Applying a suitable DC bias to the antiblooming drain provides blooming protection. The
electrons that exceed a specific level, determined by the ODB bias, are drained away from the pixels. After the
integration cycle is completed by applying a PD-cell readout pulse to IAG2, charge is transferred from the PD-cell
into the V-cell and then quickly transferred into the storage cell where it waits for readout. TC246CYM-B0
enables 2 lines to sum together to implement the pseudo-interlace scan.
Additionally, 4 dark lines, located between the image sensing area and the image-storage area, were added to
the array for isolation.
Advanced Lateral Overflow Drain
Each pixel is constructed with the advanced lateral overflow drain structure. By varying the DC bias of the
anti-blooming drain it is possible to control the blooming protection level and trade it for well capacity.
Electronic Exposure Control
Precise exposure control timing on a frame-by-frame basis is possible. The integration time can be arbitrarily
shortened from its nominal length by clearing residual charge from the PD-cell. To do this, apply a PD-cell clear
pulse to IAG2, which marks the beginning of integration.
Serial Register and Charge Multiplier
The serial register of TC246 image sensor consists of only poly-silicon gates. It operates at high speed, being
clocked from 0 V to 8 V. This allows the sensor to work at 30 frames/s. The serial register is used for transporting
charge stored in the pixels of the memory lines to the output amplifier. The TC246 device has a serial register
with twice the standard length. The first half has a conventional design that interfaces with the memory as it
would in any other CCD sensor. The second half, however, is unique and includes 400 charge multiplication
stages with a number of dummy pixels that are needed to transport charge between the active register blocks
and the output amplifier. Charge is multiplied as it progresses from stage to stage in the multiplier toward the
charge detection node. The charge multiplication level depends on the amplitude of the multiplication pulses
(approximately 15 V to 22 V) applied to the multiplication gate. Due to the double length of the register, first two
lines in each field or frame scan do not contain valid data and should be discarded.
Charge Detection Node and Buffer Amplifier
The last element of the charge detection and readout chain is the charge detection node with the buffer amplifier.
The charge detection node is using a standard Floating Diffusion (FD) concept followed by an on-chip,
dual-stage, source-follower buffer. Applying a pulse to the RST pin resets the detection node. Pixel charge
summing function can be easily implemented by skipping the RST pulses. To achieve the ultimate sensor
performance it is necessary to eliminate kTC noise. This is typically accomplished by using CDS (correlated
double sampling) processing techniques. IMPACTRON devices have the potential for detecting single electrons
(photons) when cooled sufficiently.
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