VG6640 datasheet(81/126 Pages) STMICROELECTRONICS

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VG6640, VD6640

Video system

125

7.3.2

Analog gain model

The selected analog gain applies to all of the sub-images (Long, Medium and Short). When

the Long Exposure is being taken, each pixel is read by two AD Converters simultaneously

of which one has a gain of x1 and the other, a gain of x4. These data pipes are referred to as

Long1 and Long4. These are merged at the end of the Long Integration period to give a

12bit result and stored while the Medium and Short integrations are performed. This means

that the last three analog gain options are outside the normal operating conditions and so,

should not be used.

Figure 24 describes the analog gain register (1 byte) for the image sensor.

Figure 24. Analog gain register format

Table 37 specifies the valid analog gain values for the image sensor.

The dynamic range of the pixels is increased through the capture of three different exposures from each

pixel. Only coarse integration times can be set, in multiples of lines.

Table 36. Integration time limits

Exposure

Long Exposure

Medium Exposure

Short Exposure

Variable Name

INT_LONG_LINE

INT_MED_LINE

INT_SHORT_LINE

Purpose

Coarse Long Integration

Time in Num of Lines

Coarse Med Integration

Time in Num of Lines

Coarse Short Integration

Time in Num of Lines

course_time_long

course_time_medium

course_time_short

Minimum Value (lines)

Maximum Value (lines)

FRAMELENGTH_LINES -

115

Other Limits

<= OFFSET_L-2

<= OFFSET_M-2

<= OFFSET_S-2

Fine Exposure (pixel clks)

812

398

A3 A2 A1 A0

A5 A4

Coarse gain

Not used

Table 37. Analog gain control

Gain value

Coarse gain code [A3:A0]

Analog gain(L1)

Analog gain(L4)

0x00

0000

0.0 dB (x1.00)

0.0 dB (x4.00)

0x01

0001

0.6 dB (x 1.07)

0.6 dB (x 4.28)

0x02

0010

1.2 dB (x1.1)

1.2 dB (x4.4)

0x03

0011

1.8 dB (x1.2)

1.8 dB (x4.8)

0x04

0100

2.5 dB (x1.3)

2.5 dB (x5.2)

0x05

0101

3.3 dB (x1.5)

3.3 dB (x6.0)

0x06

0110

4.1 dB (x1.6)

4.1 dB (x6.4)

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