THS7303 Datasheet, PDF (28/43 Pages) Texas Instruments – 3-Channel Low Power Video Amplifier with I2C Control, Selectable Filters, 6-dB Gain, SAG Correction, 2:1 Input MUX, and Selectable Input Bias Modes

THS7303
SLOS479 – OCTOBER 2005
www.ti.com
APPLICATION INFORMATION (continued)
As with the dc output mode of operation, each line should have a 75-Ω source termination resistor in series with
the ac-coupling capacitor. If 2 lines are to be driven, it is best to have each line use its own capacitor and resistor
rather than sharing these components as shown in Figure 65.This helps ensure line-to-line dc isolation and other
potential problems. Using a single 1000-µF capacitor for 2-lines can be done, but there is a chance for ground
loops and interference creation between the two receivers.
3.3 V
DAC /
Y’
Encoder
(THS8200)
HDTV
480i
576i
P’_B
480p
576p
720p
1080i
P’_R
1080p
Y’
P’_B
P’_R
R
R
R
0.1 mF
75 W
1 mF
75 W
1 mF
75 W
DC + 135 mV
1 NC
NC 20
DC + 135 mV
DC + 135 mV
AC STC
AC Bias
AC Bias
2 CH.1 IN A
3 CH.2 IN A
4 CH.3 IN A
5 _{CH.1 IN B}
6 CH.2 IN B
7 CH.3 IN B
CH.1 OUT 19
CH.1 SAG 18
CH.2 OUT 17
CH.2 SAG 16
CH.3 OUT 15
CH.3 SAG 14
8 I2C-A1
SCL 13
9 I2C-A0
SDA 12
10 GND
VS+ 11
0.01 mF
3.3 V
100 mF
2
IC
Controller
470 mF
(See Note A)
+
Y’
Out 1
75 W
470 mF
(See Note A)
+
Y’
Out 2
470 mF
(See Note A)
+
75 W
P’ B
Out 1
75 W
470 mF
P’B
(See Note A) ^{Out 2}
+
75 W
470 mF
(See Note A)
+
P’ _R
Out 1
75 W
470 mF
(See Note A)
+
P’R
Out 2
75 W
75 W
75 W
75 W
75 W
75 W
75 W
External
Input
A. Due to the high frequency content of the video signal, it is recommended, but not required, to add a 0.01-µF capacitor
in parallel with these large capacitors.
Figure 65. Typical Y'P'_BP'_R System Driving 2 AC-Coupled Video Lines
Due to the edge rates and frequencies of operation, it is recommended – but not required – to place a 0.1-µF to
0.01-µF capacitor in parallel with the large 220-µF to 1000-µF capacitors. These large value capacitors are most
commonly aluminum electrolytic. It is commonly known that these capacitors have significantly large equivalent
series resistance (ESR), and their impedance at high frequencies is large due to the associated inductances
involved with their construction. The small 0.1-µF to 0.01-µF capacitors help pass these high frequency (>1 MHz)
signals with lower impedance than the large capacitors. This is especially true when HD and computer R'G'B'
signals are being used. Their associated edge rates and frequency content can reach beyond 30-MHz for HD
signals and can be over 100-MHz for R'G'B' signals – frequencies that typical aluminum electrolytic capacitors
typically cannot pass effectively.
Although it is common to use the same capacitor values for all the video lines, the frequency bandwidth of the
chroma signal in a S-Video system are not required to go as low or as high as the frequency of the luma
channel. Thus, the capacitor values of the chroma line(s) can be smaller – such as 0.1 µF.
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