TC281_03 Datasheet, PDF (7/18 Pages) Texas Instruments – PIXEL CCD IMAGE SENSOR

TC281
1036- × 1010-PIXEL CCD IMAGE SENSOR
SOCS058D – JUNE 1996 – REVISED MARCH 2003
advanced lateral overflow drain (continued)
Applying a 10-V pulse for a minimum duration of 1 µs above the nominal dc bias level causes the charge in the
image area to be completely cleared. This feature permits a precise control of the integration time on a
frame-by-frame basis. The single-pulse clear capability also reduces smear by eliminating accumulated charge
from the pixels before the start of the integration (single-sided smear).
Application of a negative 2-V pulse during the parallel transfer is recommended to prevent possible artifacts
resulting from slight column-to-column pixel well capacity variations.
storage area
A metal light shield covers the storage area to prevent a further integration of charge when charge is being
stored before readout. To use the sensor in a single-shot mode after being dormant for a long period of time,
you must perform multiple storage area clears to ensure the complete charge removal (see Figure 4).
serial register
The serial register shifts the data out of the sensor area at a maximum rate of 40 MHz, thus achieving a
1000 x 1000 pixel readout with the frame rate of 30 frames per second. The data is shifted to the BCD node
on the falling edge of the SRG clocking pulses.
The data can also be transferred out of the serial registers in a parallel direction to the clear drain. This allows
partial line readouts. The timing for this operating mode consists of transferring the next row from the storage
into the serial register while also clocking the TRG. Binning of multiple pixels within a column to increase the
device sensitivity can be performed by multiple line transfers into the serial register prior to the register readout.
The timing for this mode of operation is shown in Figure 5. Care must be taken not to exceed the well capacity
of the serial register by transferring too many lines into it. Horizontal binning is also possible in this sensor. It
can be accomplished in the BCD detection node by a suitable skipping of the reset pulses.
bulk charge detection node and output amplifier
The TC281 image sensor uses a patented TI charge detection device called the bulk charge detection node.
In this node, the signal electron packets are transferred under a uniquely designed p-channel MOS transistor
where they modulate the transistor threshold voltage. The threshold voltage changes are then detected; they
represent the desired output signal. After sensing is completed, charge is removed from the node by applying
a reset pulse. One of the key advantages of the BCD charge detection concept is that charge is sensed
nondestructively. The nondestructive readout does not generate reset noise, eliminating the need for the CDS
post processing. Other advantages are high speed and low noise.
Emitter-follower output buffering is recommended for the TI image sensors. TI also recommends that the
emitter-follower be ac coupled to the rest of the signal processing chain. ac coupling eliminates problems with
the sensor output dc stability and the sensor-to-sensor dc output level variations.
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