TDA8722 View Datasheet(PDF) - Philips Electronics
Part Name
Description
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TDA8722 Datasheet PDF : 28 Pages
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Philips Semiconductors
I2C-bus programmable modulator for
negative video modulation and FM sound
Product specification
TDA8722
PINNING
SYMBOL PIN
DESCRIPTION
AUDIO 1 audio input
SOSCA 2 sound oscillator A
SOSCB 3 sound oscillator B
UOSCB 4 UHF oscillator B
OGND
5 RF oscillator ground
UOSCA 6 UHF oscillator A
AMP
7 tuning amplifier output
CP
8 charge pump output
XTAL
9 crystal oscillator
DGND 10 digital ground
VDDD
SCL
SDA
11 digital supply voltage
12 serial clock input (I2C-bus)
13 serial data input (I2C-bus)
P0
14 NPN open-collector output Port
RFB
15 asymmetrical RF output B
RFA
16 asymmetrical RF output A
ADJUST 17 modulation depth and picture-to-sound
distance adjustment pin
AGND
18 analog ground
VIDEO 19 video input
VDDA
20 analog supply voltage
handbook, halfpage
AUDIO 1
SOSCA 2
20 VDDA
19 VIDEO
SOSCB 3
18 AGND
UOSCB 4
17 ADJUST
OGND 5
UOSCA 6
16 RFA
TDA8722
15 RFB
AMP 7
14 P0
CP 8
13 SDA
XTAL 9
12 SCL
DGND 10
11 VDDD
MBE394
Fig.2 Pin configuration.
FUNCTIONAL DESCRIPTION
The TDA8722 is a programmable modulator which can be
divided into two main blocks:
• A modulator for negative video modulation and
FM sound TV standards
• A programmable PLL frequency synthesizer.
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
and ground (R17). The value can change between 47 kΩ
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
−10 and −18 dB (see Fig.11).
1998 Jun 23
5
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