1997 Jan 06
10
Philips Semiconductors
Preliminary specication
Digital Video Encoder (ConDENC)
SAA7120; SAA7121
Fig.7 Teletext timing.
handbook, full pagewidth
tTTXWin
tTTX
tPD
tFD
CVBS/Y
TTX
TTXRQ
textbit #:
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10 11
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18 19 20
21
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MBH788
Analog output voltages
The analog output voltages are dependent on the
open-loop voltage of the operational amplifiers for
full-scale conversion (typical value 1.35 V), the internal
series resistor (typical value 2
), the external series
resistor and the external load impedance.
The digital output signals in front of the DACs under
nominal conditions occupy different conversion ranges, as
indicated in Table 1 for a 100
100 colour bar signal.
Values for the external series resistors result in a 75
load.
Input levels and formats
The ConDENC expects digital Y, Cb, Cr data with levels
(digital codes) in accordance with
“CCIR 601” (see
Tables 2 and 3).
For C and CVBS outputs, deviating amplitudes of the
colour difference signals can be compensated by
independent gain control setting, while gain for luminance
is set to predefined values, distinguishable for 7.5 IRE
set-up or without set-up.
Reference levels are measured with a colour bar,
100% white, 100% amplitude and 100% saturation.
Table 1
Digital output signals conversion range
Table 2
“CCIR 601” signal component levels
CONVERSION RANGE (peak-to-peak) (digits)
CVBS, SYNC
TIP-TO-PEAK CARRIER
Y (VBS) SYNC
TIP-TO-WHITE
1016
881
COLOUR
SIGNALS
YCb
Cr
White
235
128
Yellow
210
16
146
Cyan
170
166
16
Green
145
54
34
Magenta
106
202
222
Red
81
90
240
Blue
41
240
110
Black
16
128