ADV7301AKST Analog Devices Inc, ADV7301AKST Datasheet - Page 44

• Manufacturer Part Number: ADV7301AKST
• Description: IC DAC VIDEO HDTV 6-12BIT 64LQFP
• Manufacturer: Analog Devices Inc
• Type: Video Encoderr

Specifications of ADV7301AKST

• Rohs Status: RoHS non-compliant
• Applications: DVD, Set-Top Boxes
• Voltage - Supply, Analog: 2.37 V ~ 2.63 V
• Voltage - Supply, Digital: 2.37 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 64-LQFP
• Number Of Dac's: 6
• Adc/dac Resolution: 12b
• Screening Level: Commercial
• Package Type: LQFP
• Pin Count: 64
• Lead Free Status / RoHS Status: Compliant

ADV7300A/ADV7301A
Gamma Correction
[Subaddresses 21h–37h for HD;
Subaddresses 66h–79h for SD]
Gamma correction is available for SD and HD video. For each
standard there are twenty 8-bit wide registers. They are used to
program the Gamma Correction Curves A and B. HD Gamma
Curve A is programmed at Addresses 24h–2Dh and HD
Gamma Curve B at 2Eh–37h. SD Gamma Curve A is pro-
grammed at Addresses 66h–6Fh, and SD Gamma Curve B at
Addresses 70h–79h.
Generally, gamma correction is applied to compensate for the
nonlinear relationship between signal input and brightness level
output (as perceived on the CRT). It can also be applied wher-
ever nonlinear processing is used.
Gamma correction uses the function:
where
Gamma correction is performed on the luma data only. The
user has the choice to use two different curves, Curve A or
Curve B. At any one time only one of these curves can be used.
The response of the curve is programmed at 10 predefined
locations. In changing the values at these locations, the gamma
curve can be modified. Between these points, linear interpola-
tion is used to generate intermediate values. Considering the
curve to have a total length of 256 points, the 10 locations are
at: 24, 32, 48, 64, 80, 96, 128, 160, 192, and 224. Locations 0,
16, 240, and 255 are fixed and cannot be changed.
For the length of 16 to 240, the gamma correction curve must
be calculated as:
where y = gamma corrected output, x = linear input signal, and
To program the gamma correction registers, the values for y
must be calculated using the formula:
where x
32, 48, 64, 80, 96, 128, 160, 192, or 224; y
along the y-axis, which has to be written into the Gamma Cor-
rection Register.
*Rounded to the nearest integer
= the gamma power factor.
(n–16)
equals the gamma power factor.
= the value for x along the x-axis at points n = 24,
y
n
=



Signal
240 16
x
(
n
−
−
16
OUT
)
y

 ×

=
=
γ
(
x
Signal
γ
(
240 16
IN
−
)
γ
n
)
= the value for y
+
16
–44–
Example:
The gamma curves shown in Figures 61 and 62 are examples.
Any user-defined curve is acceptable in the range of 16–240.
Figure 61. Signal Input (Ramp) and Signal Output
for Gamma 0.5
300
250
200
150
100
50
0
0
y
y
y
y
y
y
y
y
y
y
128
160
192
24
32
64
80
96
224
48
=
=
=
=
=
=
=
=
=
=
























SIGNAL OUTPUT












50


































224
224
224
224
224
224
16
48
64
80
112
224
144
224
176
224
208
224
32
8
SIGNAL INPUT






























0 5
0 5
0 5
0 5
0 5
0 5
.
.
.
.
.
0 5
0 5
0 5
0 5
.
100
.
.
.
.
×
×
×
×
×
×
×
×
×
×
LOCATION
224
224
224
224
224
224
224
224
224
224








































150
+
+
+
+
+
+
+
+
+
+
16
16
16 120
16 136
16 150
16 101
16 174
16
16
0.5
16
=
=
=
=
=
=
=
= =
=
=
58
76
195
214
232
200
*
*
*
* *
*
*
*
*
*
*
250
REV. A