Changes To Check The Value Of Each Coefficient Section - Analog Devices Advantiv ADV7619 Hardware User's Manual

UG-237
The ranges of the three equations are shown in Table 44.
Table 44. Equation Ranges
Equation Minimum Value
Y 0 + 0 + 0 = 0
Pb (−0.34) + (−0.17) = −0.51
Pr (−0.43) + (−0.08) = −0.51
As can be seen from this table, the range for the Y component fits into the CSC operating range. However, the Pb and Pr ranges slightly
exceed the range. To bring all equations back into the supported range, they should be scaled back by 1/1.02.
If equations fall outside the supported range, overflow or underflow can occur and undesirable wrap around effects (large number
overflowing to small ones) can happen.
. 0 59 0 3 .
= × + ×
Y G R
. 1 02 . 1 02
− −
. 0 34 . 0 17
= × +
Pb G
. 1 02 . 1 02
−
. 0 43 . 0 51
= × + ×
Pr G
. 1 02 . 1 02
Note that the scaling of the dynamic range does not affect the static offset.
Check the Value of Each Coefficient
The maximum value for each coefficient on its own can only be within the range of −4096/+4096 to 4095/4096, which
equals [1... +0.999755859375]. Values outside this range do not fit into the 12-bit fixed point format used to program the
coefficients.
If the value of one or more coefficients after scaling of the overall equation exceeds the supported coefficient range, the CSC_SCALE[1:0]
should be set.
With the CSC_SCALE[1:0] set high, all coefficients must be scaled by half, which makes them fit into the given coefficient range. The
overall outputs of the CSC are gained up by a fixed value of two, thus compensating for the scaled down coefficients.
In the preceding example, each coefficient on its own is within the range of
−
4095 4095
≤ ≤
Coeff
4096 4096
Therefore, all coefficients can be programmed directly and the CSC_SCALE[1:0] bit should be set to 0.
Notes
•
To achieve a coefficient value of 1.0 for any given coefficient, CSC_SCALE should be set high and the coefficient should actually be
programmed to a value of 0.5. Otherwise, the largest value would be 4095/4096 = 0.9997, which is not exactly 1. While this value
could be interpreted as a 1, it is recommended to use the value of 0.5 and the CSC_SCALE bit for maximum accuracy.
•
For very large coefficient values, for example, 2.58, a combination of CSC_SCALE[1:0] and equation scaling should be used.
•
Set CSC_SCALE high (2.58/2 = 1.29) and scale the overall equation by slightly more than 1.28 (coefficient falls within the supported
range of [−0.999 ... +0.999]).
. 0 11
+ × = × + ×
B . 0 58 G . 0 29
. 1 02
. 0 51
× + × + = −
R B 2048 . 0 33
. 1 02
−
. 0 08
+ × + = −
R B 2048 . 0 42
. 1 02
Maximum Value
0.59 + 0.3 + 0.11 = 1
0.51
0.51
+ ×
R . 0 11 B
× − × + × +
G . 0 17 R 0 5 . B 2048
× + × − × +
G 0 5 . R . 0 08 B 2048
Rev. A | Page 114 of 204
Hardware User Guide
Range
[0 ... 1] = 1
[−0.51 ...+ 0.51] = 1.02
[−0.51 ... +0.51] = 1.02