Datasheet

ADA4830-1/ADA4830-2 Data Sheet
Rev. C | Page 16 of 22
USING THE ADA4830-2 AS A LOW COST VIDEO
SWITCH
Figure 34 shows a video multiplexer/switch using the ADA4830-2,
dual, high speed difference amplifier. This circuit allows the user
to input two remote video sources into a single channel of a video
decoder, such as the ADV7180.
Traditional CMOS multiplexers and switches suffer several
disadvantages at video frequencies where their on-resistance
introduces distortion, degrades differential gain and phase
performance, and interacts with the termination resistor to
attenuate the incoming video signal and affect the luminance.
System designers generally address these issues by adding
external buffers to add gain and increase drive capability.
Video multiplexing can be simplified by using high speed video
amplifiers with a disable/enable function (sometimes called power-
down). When the amplifier is disabled, its output stage goes into
a high impedance state, allowing several amplifier outputs to be
wired together. High speed video op amps have all the key features
required to make them ideal for this function. Their high input
impedance does not affect the characteristic impedance of the
transmission line, thus allowing back termination. They also have
inherently good video specifications, including differential gain and
phase, slew rate, bandwidth, and 0.1 dB flatness.
Each channel of the ADA4830-2 is a high speed difference
amplifier circuit that eliminates common-mode noise and phase
noise caused by ground potential differences between the incoming
video signal and the receiver. The ADA4830-2 also offers integrated
short-to-battery protection and heightened ESD tolerance in a
small foot print. The fault detection output (the STB pins) of the
ADA4830-2 allows for proactive wire diagnostics when connected
to a microcontroller or video decoder and are used to generate
an interrupt during a fault condition.
ADA4830-2
INP1
GND2 VREF2 +VS2
0.1µF
ENA2
ENABLE2
(INPUT)
+V
S
4.7µF
4.7µF
VREF1
+VS1
GND1
ENA1
VOUT1
VOUT2
STB1
STB2
5kΩ5kΩ
+V
S
+V
S
1
2
3
4
6 7 85
12
11
10
9
15 14 13
16
75Ω
75Ω
75Ω
DIFFERENTIAL
INPUT 1
75Ω
75Ω
DIFFERENTIAL
INPUT 2
CONNECT
TO VIDEO
DECODER
75Ω
INN1
INN2
INP2
STB FLAGS
(OUTPUTS)
2.2µF
0.1µF
+
ENABLE1
(INPUT)
10020-049
Figure 34. Low Cost Video Switch Using the ADA4830-2