TC281

1036-

× 1010-PIXEL CCD IMAGE SENSOR

SOCS058B – JUNE 1996 – REVISED MAY 1999

7

POST OFFICE BOX 655303

advanced lateral overflow drain (continued)

Application of a negative 2-V pulse during the parallel transfer is recommended to prevent possible artifacts 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. When the sensor is to be used in a single-shot mode and is dormant for a long period

of time, it is necessary to 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 gate. Binning of multiple pixels within a column together to

increase the device sensitivity is possible 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 structure, 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 and 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, therefore, eliminating the

need for the CDS post processing. Other advantages are high speed and a very low noise.

Emitter-follower output buffering is recommended for the TI image sensors. Also, it is recommended 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.