VV6850 View Datasheet(PDF) - Vision

Part Name

Description

View to exact match

VV6850

High resolution CMOS Image Sensor with support for external FPN cancellation and serial interface control, available in colour (6850) and monochrome (5850) versions

Vision 

Video Output

Black Reference Lines

There are six lines at the bottom of the pixel array that are covered with opaque masking. These

black reference lines have their own reset shift register. A four to one multiplexer, controlled by

Control Register bits CR[4] and CR[3], selects the input to this shift register (FBCK), and hence

the operating mode. The four modes of operation are:

1. Permanent Reset - By setting FBCK low, the black lines are permanently reset to VRT.

2. Minimum Integration - FBCK follows the field read pulse, FR; the black reference lines are

held in minimum exposure.

3. Integration - FBCK follows the field read pulse, FI; the black reference lines therefore have the

same exposure time as the array.

y 4. Permanent integration; the reference lines continue to integrate until reset as in 1.

r Option 1. is the most stable as it does not depend on either the quality of the black shield above

the black pixels or any light incident on the pixels. However it is also the least accurate as it does

a not allow for dark current or the breakthrough of the falling edge of the pixel reset signal onto the

pixel capacitance. The resulting reference value will be ‘blacker’ than black due to the above

errors.

Option 2. is more accurate than option 1. as the effect of the pixel reset signal breakthrough is

included, but the effect of total dark current is not included since the black reference pixels are not

n integrating for the same time as the image section of the pixel array. The reference is, also, now

i sensitive to the effects of light reaching the black line pixels.

Option 3. includes the effect of dark current since the black reference pixels are integrating for the

same time as the image section of the pixel array. The validity of the reference is, however, now

even more sensitive to the effects of light reaching the pixel.

m Option 4. in combination with option 1 allows the exposure time for the black reference lines to be

i controlled independently of the exposure of the rest of the image.

l Note: For best results, it is recommended that the average of the four central lines of the black

reference line group is used to characterise ‘Black’ for the frame.

r e Exposure Control

Exposure control is achieved either electronically by varying the FI pulse duration, or directly by

P means of a shutter arrangement (mechanical, electro-mechanical, electro-optical, and so on). The

correct exposure level for any scene can be assessed by processing a ‘trial exposure’ of the

scene, or by utilising the ‘Accumulate’ or ‘Parallel Integration’ operating mode.

See: OPERATING MODES for a full description of exposure control.

16/06/97

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