Datasheet

+
-
75 Ω
75 Ω
1.24 kΩ1.24 kΩ
5 V
Input Range
= 1 V to 2.25 V
Output Range
= 2 V to 4.5 V
R
T
V
O
Range
= 0 V to 1.25V
470 µF
+
-
75 Ω
75 Ω
1.24 kΩ1.24 kΩ
5 V
Input Range
= 1 V to 2.25 V
Output Range
= 2 V to 4.5 V
R
T
V
O
Range
= 0 V to 1.25V
22 µF
1.24
kΩ
22 µF
+
−
75 Ω
75 Ω
1.24 kΩ1.24 kΩ
5 V
Input Range
= 1 V to 2.25 V
Output Range
= 2 V to 4.5 V
R
T
V
O
Range
= 1 V to 2.25 V
SN10501
SN10502
SN10503
SLOS408B – MARCH 2003 – REVISED JANUARY 2009 .................................................................................................................................................. www.ti.com
Similar performance is observed for negative video
signals. In practice, similar performance is achieved
even with three video loads as shown in Figure 37
due to the linear high-frequency output impedance of
the SN1050x. This circuit is suitable for driving video
cables, provided that the length does not exceed a
few feet. If longer cables are driven, the gain of the
SN1050x can be increased to compensate for cable
loss.
Configuring the SN1050x for single-supply video
applications is easily done, but attention must be
given to input and output bias voltages to ensure Figure 39. AC-Coupled Output Single-Supply
Video Amplifier
proper system operation. Unlike some video
amplifiers, the SN1050x input common-mode voltage
range does not include the negative power supply,
In some systems, the physical size and/or cost of a
but rather it is about 1-V from each power supply. For
470- µ F capacitor can be prohibitive. One way to
split supply configurations, this is very beneficial. For
circumvent this issue is to use two smaller capacitors
single-supply systems, there are some design
in a feedback configuration as shown in Figure 40 .
constraints that must be observed.
This is commonly known as SAG correction. This
circuit increases the gain of the amplifier up to 3 V/V
Figure 38 shows a single-supply video configuration
at low frequencies to counteract the increased
illustrating the dc bias voltages acceptable for the
impedance of the capacitor placed at the amplifier
SN1050x. The lower end of the input common-mode
output. One issue that must be resolved is that the
range is specified as 1 V. The upper end is limited to
gain at low frequencies is typically limited by the
4 V with the 5-V supply shown, but the output range
power-supply voltage and the output swing of the
and gain of 2 limit the highest acceptable input
amplifier. Therefore, it is possible to saturate the
voltage to 4.5 V / 2 = 2.25 V. The 4.5-V output is
amplifier at these low frequencies if full analysis is not
what is typically expected with a 150- Ω load. It is
done on this system which includes both input and
easily seen that the input and output voltage ranges
output requirements.
are limiting factors in the total system. Both
specifications must be taken into account when
designing a system.
Figure 40. AC-Coupled SAG Corrected Output
Single-Supply Video Amplifier
Figure 38. DC-Coupled Single-Supply Video
Amplifier Many times the output of the video encoder or DAC
does not have the capability to output the 1-V to
2.25-V range, but rather a 0-V to 1.25-V range. In this
In most systems, this may be acceptable because
instance, the signal must be ac-coupled to the
most receivers are ac-coupled and set the black level
amplifier input as shown in Figure 41 . Note that it
to the desired system value, typically 0 V (0-IRE).
does not matter what the voltage output of the DAC
But, to ensure full compatibility with any system, it is
is, but rather the voltage swing should be kept less
often desirable to place an ac coupling capacitor on
than 1.25 V
PP
.
the output as shown in Figure 39 . This removes the
dc-bias voltage appearing at the amplifier output. To
minimize field tilt, the size of this capacitor is typically
470 µ F, although values as small as 220 µ F have
been used with acceptable results.
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