5. Imager operation

5.1. General remarks

The epc901 line imager chip is based on a backside illumination technology (BSI). The image is taken from the backside of the chip,

whereas the electrical circuits and the pins are on the frontside. Thus, the chip must be flip-chip mounted to the PCB in order to expose the

backside to the incoming light.

It is not possible with BSI to shield the photosensitive area with an integrated, electrically controlled shutter when there no light shall be

detected. In other words, the pixel CCD is continuously photo-sensitive and collects charge generated by the detected photons (unwanted

exposure). Thus, the CCD must be flushed or erased by the unwanted charge before an image can be acquired.

READ Pulse - The pulse applied to pin READ_CLK to initiate the read-out of a frame.

READ Clock - The clock applied to pin READ_CLK to read out the frame (after the Read Pulse).

5.2. Image acquisition

After the exposure time defined by the user, the charge collected in the CCD has to be shifted into an area which is not photo-sensitive.

This area is called frame store. The shift process samples the charge collected by the CCD in the frame store. The following diagram

shows this operation.

SHUTTER

CCD operation

T

FLUSH

T

SHIFT

exposure time

DATA_RDY

automatic

CCD flush

automatic

shift to frame

store (FIFO)

exposure to

acquire an

image

(unwanted)

exposure

(unwanted)

exposure

T

FLUSH

flush CCD

CLR_PIX

T

PULSE_CLR_PIX

Figure 7: Image acquisition timing

The acquisition of a frame is controlled by a pulse on pin SHUTTER (see Figure 7). The rising edge of a pulse on SHUTTER triggers the

internal flush operation to erase the CCD from any unwanted electrons prior to the exposure. The exposure starts automatically after the

flush operation is completed. The CCD collects electrons thereafter as long as the SHUTTER pin is high. Upon the falling edge of

SHUTTER, the charge collected in the CCD pixel field is automatically shifted to the CCD frame store which is a photo-insensitive area

(see (1) in Figure 8). As soon as the frame is ready for read-out, the signal DATA_RDY goes high. The image is ready to be readout as

described in section 5.4..

SHUTTER

READ_CLK

T

CDS

T

SHIFT

(1)

(2)

(3)

DATA_RDY

Figure 8: Illustrative example of single-frame acquisition and read-out

© 2016 ESPROS Photonics Corporation

Characteristics subject to change without notice

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