MC44002 MC44007
17
MOTOROLA ANALOG IC DEVICE DATA
calibration gate (CAL) and integrated by an external
capacitor on Pin 11. The resulting voltage VEXT is then
transformed to generate the ADJUST control voltage
removing from the loop range most of the variations due to
internal RC products and temperature.
Color Difference Stages
This stage accepts luminance and color difference
signals, together with external R,G,B and Fast Commutation
inputs and carries out various functions on them, including
clamping, blanking, switching and matrixing. The outputs,
consisting of processed R,G,B signals, are then passed to
the Auto Gray Scale section.
A block diagram of this stage is shown in Figure 10. The
Y2, R-Y, B-Y together with R, G and B are all external inputs
to the chip. The Y1 signal comes from the decoder section.
Each of the signals is back-porch clamped and then blanked.
The Y2 and R,G,B inputs have their own simple sync
separators, the output from which may be used as the
primary synchronization for the chip by means of commands
from the MCU.
The Fast Commutation is an active high input used to drive
a high speed switch; for switching between the Y and color
difference inputs and the R,G,B (text) inputs.
After blanking, the Y1 and Y2 channels go to the Luma
Selector which is controlled by means of 2 bits from the MCU.
From here the selected luma signal goes to the RGB matrix.
The two color difference signals pass through the saturation
control. From here they go to a matrix in which G-Y is
generated from the R-Y and B-Y, and lastly, to another matrix
where Y is added to the three color difference signals to
derive R,G,B.
Control bits (via the I2C bus) allow the matrix coefficients
to be adjusted in order to suit different requirements,
particularly in NTSC. Table 1 shows the theoretical
demodulation angles and amplitudes and the corresponding
matrix coefficient values for each of the 4 selectable modes.
(The A mode corresponds to the standard PAL/SECAM/NTSC
mode). Although primarily intended for NTSC, this feature can
also act on PAL/SECAM or external RGB signals.
The R,G,B inputs may take one of two different paths.
They may either go straight to the output without further
processing, or via a separate matrix and the saturation
control. The path taken is controlled in software. When the
latter route is selected, the R,G,B signals undergo a matrix
operation to derive Y. From this, R-Y and B-Y are easily
derived by subtraction from R and B; the derived color
difference signals are then subjected to saturation control.
This extra circuitry allows another feature to be added to the
TV set, namely the ability to adjust the color saturation of the
RGB inputs. After the saturation control the derived signals
are processed as before.
Table 1. Matrix Modes Coefficients
A
B
C
C
RR
1.0
1.577
1.539
1.556
RB
0
–0.156
–0.248
–0.251
GR
–0.513
–0.443
–0.462
–0.504
GB
–0.187
–0.168
–0.150
–0.125
BB
1.0
1.0
1.0
1.0
BR
0
0
0
0
Rm
0.562
0.9
0.9
0.91
Gm
0.344
0.3
0.3
0.31
Ra
90
100
106
106
Ga
237
236
240
246
NOTE:
BB = Gain of (Bout/(B–Y)in) = 1 (reference). BR = Gain of (Bout/(R–Y)in) = 0 (theoretically).
Figure 9. SECAM Decoder (MC44002 only)
Squarer
SECAM
I/P
VA1 Adjust
RC-T
Compensation
Ident
Out
De-emphasis
Tuning Offsets
Output Interface
PHIG
IRC
Fbk
ICOMP
CAL
11
SECAM
Cal
Loop
ICAL
AGC
A1
A2
CAL
X2
Timing Signals
SECAM Out
(R-Y/B-Y Sequen.)
FLL Demodulator
Phase
Detector
FLL Tracking
Filter
Loop
Filter
Cloche Filter
H
H Clamp
Calibration
Switch
Adjust
4.43MHz
Limiter
VTun