THS7303 Datasheet, PDF (22/43 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
APPLICATION INFORMATION (continued)
3.3 V
www.ti.com
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 I 2C-A1
SCL 13
9 I 2C-A0
SDA 12
10 GND
V_S+ 11
0.01 mF
Y’
470 mF _{75 W} ^Out
+
(See Note A)
P’_B
470 mF _{75 W} ^Out
+
(See Note A)
P’ R
470 mF _{75 W} ^Out
+
(See Note A)
+Vs
+
100 mF
2
IC
Controller
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 59. Typical Y'P'_BP'_R Inputs From DC-Coupled Encoder/DAC and
AC-Coupled External Inputs With AC-Coupled Line Driving
INPUT MODES OF OPERATION – DC
The inputs to the THS7303 allows for both ac coupled and dc coupled inputs. Many DAC’s or video encoders
can be dc connected to the THS7303. But, one of the drawbacks to dc coupling is when 0 V is applied to the
input of the THS7303. Although the input of the THS7303 allows for a 0-V input signal, the output swing of the
THS7303 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 THS7303, 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 THS7303 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 60.
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