TMC22191 CADEKA [Cadeka Microcircuits LLC.], TMC22191 Datasheet - Page 25

• Manufacturer Part Number: TMC22191
• Description: Digital Video Encoders/Layering Engine
• Manufacturer: CADEKA [Cadeka Microcircuits LLC.]

PRODUCT SPECIFICATION
Gamma Correction
Gamma is built into broadcast television systems as a correc-
tion factor for nonlinearity in image acquisition (nonlinear
conversion of light into current in a vidicon) and at the dis-
play (phosphor nonlinearity in converting current into light).
A Gamma corrector transfer function takes the form of
where a typical Gamma is 2.2 for NTSC, 2.8 for PAL.
Computer systems usually ignore Gamma in driving a dis-
play monitor. Each R, G, and B channel is treated as linear.
When encoding a computer display output to video, the user
must decide whether to apply a gamma correction factor and,
if so, what value. It is a good assumption that, since the digi-
tal video input over the CVBS bus is in composite form, it
has been Gamma corrected.
Gamma correction is applied in the RGB domain. When
operating in YC
601 signal, Gamma should have already been applied.
Gamma correction is readily added to the RGB transfer
equations shown in Table 4.
Video Timing
The TMC22x91 can be programmed to accommodate a wide
range of system timing requirements. With a line locked
pixel rate of 10 to 15 Mpps, the digitally synthesized hori-
zontal waveforms and subcarrier frequency and phase are
determined from 24 registers that are loaded by a controller.
Horizontal Programming
Horizontal interval timing is fully programmable, and is
established by loading the timing registers with the durations
of each horizontal element. The duration is expressed in
PCK clock cycles. In this way, any pixel clock rate between
10 MHz and 15 MHz can be accommodated, and any desired
standard or non-standard horizontal video timing may be
produced. Figure 3 illustrates the horizontal blanking inter-
val with timing register identification.
Horizontal timing parameters can be calculated as follows:
where N is the value loaded into the appropriate timing reg-
ister, and PCK is the pixel clock period.
Horizontal timing resolution is two PXCK periods. PXCK
must be chosen such that it is an even integer multiple of the
horizontal line frequency. This ensures that the horizontal
line period, H, contains an integer number of pixels. The hor-
izontal line comprises the sum of appropriate elements.
When programming horizontal timing, subtract 5 PCK
periods from the calculated values of CBP and add 5 PCK
periods to the calculated value for VA.
Output = k ( Input )
t = N x (PCK period)
H = FP + SY + BR + BU + CBP + VA
= N x (2 x PXCK period)
B
C
R
, for example when encoding a CCIR-
1/
Table 7. Horizontal Timing Specifications
Vertical Programming
Vertical interval timing is also fully programmable, and is
established by loading the timing registers with the durations
of each vertical timing element, the duration expressed in
PCK clock cycles. In this way as with horizontal program-
ming, any pixel rate between 10 and 15 Mpps can be accom-
modated, and any desired standard or non-standard vertical
video timing may be produced.
Like horizontal timing parameters, vertical timing parame-
ters are calculated as follows:
where N is the value loaded into the appropriate timing reg-
ister, and PCK is the pixel clock period.
The Vertical Interval comprises several different line types
based upon H, the Horizontal line time.
The VB and VC lines are added to produce the half-lines
needed in the vertical interval at the beginning and end of
some fields. These must properly mate with components of
the normal lines.
where Equalization HIGH and LOW pulses (EL + EH) = H/2
and the Extended Color Back Porch, XBP = VA + CBP –VB.
XBP begins after the end of burst, BU, taking the place of
CBP in vertical interval UBV lines. Figure 5 shows the verti-
cal sync and equalization pulse detail
Table 8. Vertical Timing Specifications
VB = CBP + VA - XBP = H/2 – CBPVC
Parameter
Parameter
H = (2 x SL) + (2 x SH) [Vertical sync pulses]
t = N x (PCK period)
= N x (2 x PXCK period)
= (2 x EL) + (2 x EH) [Equalization pulses]
= VA – (EL + EH) = VA – H/2
CBP
( s)
BR
BU
EH
SH
FP
SY
VA
EL
SL
H
H
NTSC-M
NTSC-M
52.6556
63.5556
63.5556
29.4778
27.1
( s)
( s)
1.5
4.7
0.6
2.5
1.6
2.3
4.7
PAL-I
51.95
PAL-I
29.65
1.65
2.25
2.55
64.0
2.35
27.3
( s)
( s)
4.7
0.9
4.7
64
TMC22091/TMC22191
PAL-M
51.692
63.492
PAL-M
63.492
29.45
4.95
2.25
4.65
27.1
( s)
( s)
1.9
0.9
1.8
2.3
25