TDA8822 Datasheet, PDF (6/28 Pages) NXP Semiconductors – Universal I2C-bus programmable RF modulator

Philips Semiconductors
Universal I²C-bus programmable RF
modulator
Preliminary specification
TDA8822
FUNCTIONAL DESCRIPTION
The TDA8822 is a programmable RF modulator which can
be divided into the following parts:
• Video part
• Audio part
• RF part.
The TPSG is activated in two ways:
– Forcing the pin TPSG to DGND in the application
(see Fig.8)
– Setting the TPSG bit to 1 via the I²C-bus, then the
TPSG pin acts as an output port, sinking current to
allow the indication of the use of the TPSG in the
application e.g. with an LED (see Fig.9).
Video part
The video part provides the following:
• The video part includes a clamping circuit which sets the
internal reference voltage to the bottom of the
synchronizing pulse. The modulation depth is adjusted
using 3 bits of the I²C-bus programming, called MD2,
MD1 and MD0. These 3 bits make 8 different values for
the modulation depth possible (see Table 1).
• After the modulation depth is set, the signal is fed
through a clip control circuit that clips the video signal to
avoid that the modulation depth becomes higher than
100%.
• The video part also contains a TPSG. This TPSG
generates a pattern that helps to tune the TV set to the
programmed channel of the modulator. The pattern
consists of a sync pulse and two vertical white bars on
the screen (see Fig.3)
Table 1 Modulation depth setting (typical values)
MD
SETTING
0
1
2
3
4
5
6
7
MD2
0
0
0
0
1
1
1
1
BIT
MD1
0
0
1
1
0
0
1
1
MD0
0
1
0
1
0
1
0
1
MODULATION
DEPTH (%)
72.5
75.0
77.5
80.0
82.5
85.0
87.5
90.0
handbook, full pagewidth
MGE675
0
5
10 15 20 25 30 35 40 45 50 55 60 65
t (µs)
Fig.3 Test pattern signal.
1997 Jan 08
6