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参数资料
| 型号： | THS7303PWRG4 |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 3 CHANNEL, VIDEO AMPLIFIER, PDSO20 |
| 封装： | GREEN, PLASTIC, TSSOP-20 |
| 文件页数： | 27/60页 |
| 文件大小： | 1980K |
| 代理商： | THS7303PWRG4 |
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+
-
Signal
Internal
Circuitry
1 kW
878 W
150 W
675 W
Out
SAG
75 W
470 F
(Optional)
m
Video
Out
R
G
75 W
Gain (V/V) = 2.553 +
1268
150 + R
G
or
R ( ) =
G
W
- 150
1268
Gain (V/V)
2.553
-
SLOS479B
– OCTOBER 2005 – REVISED MARCH 2011
INCREASING GAIN
The gain of the THS7303 can easily be increased by using the SAG pin. As a result of the resistor configuration,
a T-network in the feedback path is formed. This feedback path allows for the SAG function to work properly, but
at the same time it allows for higher gains than the default 2 V/V (6 dB). Figure 68 shows how gain is easily
increased for each channel. Be sure to keep the RG resistor as close as possible to the SAG pin to minimize any
stability concerns.
Figure 68. Increasing Output Gain of the THS7303
The formula for the gain becomes:
For example, if the desired gain is 5.6 V/V, then RG should be 267 . Note that the internal resistors do have
tolerances associated with the respective absolute values. Because of the silicon process, resistor-to-resistor
matching is very tight when looked at as a ratio to each other. Compared to an external resistor, however, there
is a greater variation in the gain of the system.
There are a few drawbacks when implementing this feature. One concern is that the SAG functionality no longer
can be used. A second drawback is that the offset voltage increases proportionally with the gain. For example, if
DC + Shift mode is used (normally, this mode has approximately 290-mV offset with 2-V/V gain), then with
5.6-V/V gain the output offset voltage becomes 145 mV
× 5.6 V/V = 812 mV. As a result of this higher offset and
the potential risk of clipping of the signal on the high side, using a higher supply voltage, such as 5 V, is
recommended.
One possible option if a 3.3-V supply is desired is to use dc-only input without the level shift. The output offset is
nominally 35 mV
× Gain (V/V); or, for this example, 35 mV × 5.6 V/V = 196 mV. Even with a 100%
color-saturated CVBS signal, there should be no clipping on the high side.
One benefit of using the THS7303 for higher gain versus using the THS7353 device is the gain bandwidth
product (GBP) of the output amplifier; this characteristic becomes more important with the THS7353 because the
THS7353 is unity gain while the THS7303 is specified with a 2-V/V gain. For example, the THS7303 has a
bypass mode bandwidth of 190-MHz with a gain of 2 V/V. If the gain is increased to 4 V/V, then the bandwidth
should decrease to approximately 95 MHz. This increase should have minimal impact on any of the filter
characteristics. In comparison, the THS7353 has a bypass mode bandwidth of 150 MHz. If the THS7353 is
configured for a gain of 4 V/V, the bandwidth drops to approximately 37.5 MHz, and has an impact on the
performance of the 35-MHz filter.
Copyright
2005–2011, Texas Instruments Incorporated
33
Product Folder Link(s): THS7303
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