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參數資料
| 型號： | HA9P5020-5ZX96 |
| 廠商： | INTERSIL CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 100MHz Current Feedback Video Amplifier With Disable |
| 中文描述： | 1 CHANNEL, VIDEO AMPLIFIER, PDSO8 |
| 封裝： | ROHS COMPLIANT, PLASTIC, MS-012AA, SOIC-8 |
| 文件頁數： | 11/23頁 |
| 文件大小： | 572K |
| 代理商： | HA9P5020-5ZX96 |
11
FN2845.11
June 5, 2006
Referring to Figure 7, it can be seen that R
6
will act as a pull-up
resistor to +V
CC
if the DISABLE pin is left open. In those cases
where the enable/disable function is not required on all circuits
some circuits can be permanently enabled by letting the
DISABLE pin float. If a driver is used to set the enable/disable
level, be sure that the driver does not sink more than 20
μ
A
when the DISABLE pin is at a high level. TTL gates, especially
CMOS versions, do not violate this criteria so it is permissible to
control the enable/disable function with TTL.
Typical Applications
Two Channel Video Multiplexer
Referring to the amplifier U
1A
in Figure 8, R
1
terminates the
cable in its characteristic impedance of 75
, and R
4
back
terminates the cable in its characteristic impedance. The
amplifier is set up in a gain configuration of +2 to yield an
overall network gain of +1 when driving a double terminated
cable. The value of R
3
can be changed if a different network
gain is desired. R
5
holds the disable pin at ground thus
inhibiting the amplifier until the switch, S
1
, is thrown to
position 1. At position 1 the switch pulls the disable pin up to
the plus supply rail thereby enabling the amplifier. Since all
of the actual signal switching takes place within the amplifier,
it’s differential gain and phase parameters, which are 0.03%
and 0.03° respectively, determine the circuit’s performance.
The other circuit, U
1B
, operates in a similar manner.
When the plus supply rail is 5V the disable pin can be driven
by a dedicated TTL gate as discussed earlier. If a multiplexer
IC or its equivalent is used to select channels its logic must be
break before make. When these conditions are satisfied the
HA-5020 is often used as a remote video multiplexer, and the
multiplexer may be extended by adding more amplifier ICs.
Low Impedance Multiplexer
Two common problems surface when you try to multiplex
multiple high speed signals into a low impedance source
such as an A/D converter. The first problem is the low source
impedance which tends to make amplifiers oscillate and
causes gain errors. The second problem is the multiplexer
which supplies no gain, introduces all kinds of distortion and
limits the frequency response. Using op amps which have an
enable/disable function, such as the HA-5020, eliminates the
multiplexer problems because the external mux chip is not
needed, and the HA-5020 can drive low impedance (large
capacitance) loads if a series isolation resistor is used.
Referring to Figure 9, both inputs are terminated in their
characteristic impedance; 75
is typical for video
applications. Since the drivers usually are terminated in their
characteristic impedance the input gain is 0.5, thus the
amplifiers, U
2
, are configured in a gain of +2 to set the circuit
gain equal to one. Resistors R
2
and R
3
determine the
amplifier gain, and if a different gain is desired R
2
should be
changed according to the equation G = (1 + R
3
/R
2
). R
3
sets
the frequency response of the amplifier so you should refer
to the manufacturers data sheet before changing its value.
R
5
, C
1
and D
1
are an asymmetrical charge/discharge time
circuit which configures U
1
as a break before make switch to
prevent both amplifiers from being active simultaneously. If
this design is extended to more channels the drive logic
must be designed to be break before make. R
4
is enclosed
in the feedback loop of the amplifier so that the large open
loop amplifier gain of U
2
will present the load with a small
closed loop output impedance while keeping the amplifier
stable for all values of load capacitance.
The circuit shown in Figure 9 was tested for the full range of
capacitor values with no oscillations being observed; thus,
problem one has been solved. The frequency and gain
characteristics of the circuit are now those of the amplifier
and independent of any multiplexing action; thus, problem
two has been solved. The multiplexer transition time is
approximately 15
μ
s with the component values shown.
NOTES:
21. U
1
is HA-5020.
22. All resistors in
.
23. S
1
is break before make.
24. Use ground plane.
VIDEO INPUT #1
VIDEO INPUT #2
R
1
75
R
3
681
R
2
681
R
4
75
R
5
2000
+
-
U
1A
U
1B
R
9
75
R
10
2000
R
7
681
R
8
681
R
6
75
+5V IN
+5V
0.1
μ
F
10
μ
F
-5V IN
-5V
0.1
μ
F
10
μ
F
+
+
1
R
11
100
VIDEO OUTPUT
TO 75
LOAD
+5V
S
1
2
3
ALL
OFF
FIGURE 8. TWO CHANNEL HIGH IMPEDANCE MULTIPLEXER
HA-5020
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