CS7620-IQ 查看數據表（PDF） - Cirrus Logic
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CS7620-IQ Datasheet PDF : 70 Pages
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CS7620
4.8 General Black Level
The black loop is a feedback system that causes the ADC output to settle to 64 during the register defined black
pixels. This has the purpose of removing any CCD and system offsets and defining 64 as the known black level.
The loop has an exponential settling response and the time constant of this loop is effected by the black loop gain
and the number of black pixels to accumulate before updating the black accumulator. See Figure 10 for a block
diagram of the black level.
4.9 Black Level Control - Loop Gain, Clamp Length
Default = 0Ah; Read/Write (address 0Fh).
Bit Number
Bit Name
Default
7
blk_gain1
0
6
blk_gain0
0
5
blk_clp_15
0
4
blk_clp_14
0
3
blk_clp_13
1
2
blk_clp_12
0
1
blk_clp_11
1
0
blk_clp_10
0
Bit
Mnemonic
Function
Black Loop Gain Factor: The Black loop gain factor can be set to 1x,2x,4x,or
7
blk_gain1
8x and is simply a multiplying constant to effect the weight of each black pixel
before it is accumulated.
6
blk_gain0
00 - defines a gain of 1x
01 - defines a gain of 2x
10 - defines a gain of 4x
11 - defines a gain of 8x
5
blk_clp_15
Black Loop Clamp Length: The black clamp length effects the loop time con-
4
blk_clp_14
stant and also acts to average out noise in the black level. The larger this val-
3
blk_clp_13
ue the more pixels that are summed before the loop is updated which causes
greater averaging and a smaller settling time constant.
2
blk_clp_12
1
blk_clp_11
Table 11 shows the black loop time constant for various settings of Offset
Range (register 06h, bit 0) and Fixed Gain Settings (register 16h, bits 5-3).
0
blk_clp_10
Fixed Gain
(Register 16h)
not fixed
x1
x2
x4
x8
Offset Range = 1
Offset Range = 0
-1/(ln(1-nK))(1/fu)
-1/(ln(1-nK/8))(1/fu)
-1/(ln(1-nK/4))(1/fu)
-1/(ln(1-nK/2))(1/fu)
-1/(ln(1-nK))(1/fu)
-1/(ln(1-nK/2))(1/fu)
-1/(ln(1-nK/16))(1/fu)
-1/(ln(1-nK/8))(1/fu)
-1/(ln(1-nK/4))(1/fu)
-1/(ln(1-nK/2))(1/fu)
Table 11. Black Loop Time Constant
Where:
K = 1/256*blk_gain
n = Black loop clamp length = blk_clp_l[5:0]
fu = update rate
DS301PP2
33
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