TDA8722 Philips Semiconductors, TDA8722 Datasheet - Page 5

• Manufacturer Part Number: TDA8722
• Description: I2C-bus programmable modulator for negative video modulation and FM sound
• Manufacturer: Philips Semiconductors

Philips Semiconductors
PINNING
FUNCTIONAL DESCRIPTION
The TDA8722 is a programmable modulator which can be
divided into two main blocks:
The video part of the modulator consists of a clamping
circuit which sets the internal reference voltage to the
bottom of the synchronizing pulse, followed by a white clip
which avoids over modulation in case the video signal is
too strong. Typically, the IC starts to clip the video signal
when the voltage at the video input (pin 19) is
>560 mV (p-p) while the normal voltage at the video input
is 500 mV (p-p). This clipping function ensures that the
video modulation depth is not too high. The modulation
depth is adjusted in the application between at least
65 and 90% by changing the resistor value between pin 17
1998 Jun 23
SYMBOL PIN
AUDIO
SOSCA
SOSCB
UOSCB
OGND
UOSCA
AMP
CP
XTAL
DGND
V
SCL
SDA
P0
RFB
RFA
ADJUST
AGND
VIDEO
V
DDD
DDA
A modulator for negative video modulation and
FM sound TV standards
A programmable PLL frequency synthesizer.
I
negative video modulation and FM sound
2
C-bus programmable modulator for
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12
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14
15
16
17
18
19
20
11
1
2
3
4
5
6
7
8
9
audio input
sound oscillator A
sound oscillator B
UHF oscillator B
RF oscillator ground
UHF oscillator A
tuning amplifier output
charge pump output
crystal oscillator
digital ground
digital supply voltage
serial clock input (I
serial data input (I
NPN open-collector output Port
asymmetrical RF output B
asymmetrical RF output A
modulation depth and picture-to-sound
distance adjustment pin
analog ground
video input
analog supply voltage
DESCRIPTION
2
2
C-bus)
C-bus)
5
and ground (R17). The value can change between 47 k
and infinite (R17 removed); see Fig.10.
The video part also contains a test pattern signal generator
to simplify the adjustment of the receiving channel of the
TV set to the required channel of the modulator. The
pattern consists of a synchronization pulse and two
vertical white bars on screen (see Fig.3).
The audio part of the modulator contains an FM sound
modulator. The frequency of the sound subcarrier is set in
the application by external components (C3, L3 and R3).
The difference between the video carrier level and the
sound subcarrier level is adjusted in the application by
changing the value of the capacitor between pin 17 and
ground (C17). The value can change between
0 and 47 pF. The distance between the video carrier and
the sound subcarrier can be adjusted between at least
handbook, halfpage
10 and 18 dB (see Fig.11).
UOSCB
UOSCA
SOSCA
SOSCB
AUDIO
OGND
DGND
XTAL
AMP
CP
Fig.2 Pin configuration.
10
1
2
3
4
5
6
7
8
9
TDA8722
MBE394
20
19
18
17
16
15
14
13
12
11
Product specification
V DDA
VIDEO
AGND
ADJUST
RFA
RFB
P0
SDA
SCL
V DDD
TDA8722