THS7313 Datasheet, PDF (19/48 Pages) Texas Instruments – 3-Channel Low Power SDTV Video Amplifier with I2C Control, 6-dB Gain, SAG Correction, 2:1 Input MUX, and Selectable Input Bias Modes

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3.3 V
APPLICATION INFORMATION (continued)
THS7313
SLOS483 – NOVEMBER 2005
DAC /
Encoder
CVBS
(THS8200)
R
SDTV
CVBS
Y’
S-Video Y’
S-Video C’
R
480i
576i
G’B’R’
C’
R
CVBS
S-Video Y’
0.1 mF
75 W
0.1 mF
75 W
0.1 mF
DC + 135 mV
1 NC
NC 20
DC + 135 mV
DC + 135 mV
AC STC
AC STC
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 I 2C-A1
SCL 13
9 I 2C-A0
10 GND
SDA 12
V_S+ 11
0.01 mF
470 mF
+
CVBS
75 W ^Out
(See Note A)
75 W
470 mF _{75 W}
+
(See Note A)
S-Video
0.1 mF
+
75 W
+Vs
+
100 mF
2
IC
Controller
Y’
Out
C’
75 W
Out
S-Video C’
External
Input
75 W
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 47. Typical SDTV CVBS/Y'/C' Inputs From DC-Coupled Encoder/DAC and
AC-Coupled External Inputs With AC-Coupled Line Driving
75 W
INPUT MODES OF OPERATION – DC
The inputs to the THS7313 allows for both ac coupled and dc coupled inputs. Many DAC’s or video encoders
can be dc connected to the THS7313. But, one of the drawbacks to dc coupling is when 0 V is applied to the
input of the THS7313. Although the input of the THS7313 allows for a 0-V input signal, the output swing of the
THS7313 cannot yield a 0-V signal. This applies to any traditional single-supply amplifier due to the limitations of
the output transistors. Both CMOS and bipolar transistors cannot go to 0 V while sinking a significant amount of
current. This trait of a transistor is also the same reason why the highest output voltage is always less than the
power supply voltage when sourcing a significant amount of current.
The internal gain is fixed at 6 dB (2 V/V) regardless of the configuration of the THS7313, and dictates what the
allowable linear input voltage range is without clipping concerns. For example, if the power supply is set to 3 V,
the maximum output is about 2.9 V. Thus, to avoid clipping, the allowable input is 2.9 V / 2 = 1.45 V. This is true
for up to the maximum recommended 5-V power supply that allows about a 4.9 V / 2 = 2.45 V input range while
avoiding clipping on the output.
The input impedance of the THS7313 in this mode of operation is >1 MΩ. This is due to the input buffer being
configured as a unity gain amplifier as shown in Figure 48.
19