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ADA4830-2BCPZ-R7

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
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
Data Sheet ADA4830-1/ADA4830-2
Rev. C | Page 17 of 22
DRIVING CAPACITIVE LOADS
The ADA4830-1 and ADA4830-2 are capable of driving large
capacitive loads while maintaining its rated performance.
Several performance curves vs. capacitive load are shown in
Figure 12 and Figure 25. Capacitive loads interact with an op amp’s
output impedance to create an extra delay in the feedback path.
This reduces circuit stability and can cause unwanted ringing
and oscillation.
The capacitive load drive of the ADA4830-1and ADA4830-2 can
be increased by adding a low valued resistor, R
S
, in series with the
capacitive load. Figure 35 shows the test circuit.
ADA4830-1
+
–
C
L
= 47pF
R
S
= 49.9Ω
R
L
= 1kΩ
10020-052
Figure 35. R
S
Test Circuit
Introducing a series resistor tends to isolate the capacitive load
from the feedback loop, thereby diminishing its influence. One
drawback to this approach is a slight loss of signal amplitude.
Figure 36 shows the effects of a series resistor on the capacitive
drive. For very large capacitive loads, the frequency response of
the amplifier is dominated by the roll-off of the series resistor
and capacitive load.
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 50 100 150 200 250
V
OUT
(V)
TIME (ns)
10020-135
+V
S
= 5V
R
L
= 1kΩ
C
L
= 47pF
NO R
S
R
S
= 49.9Ω
Figure 36. Pulse Response With and Without Series Resistor
Another method of reducing the resonant peaking caused by
driving large capacitive loads at the output of the ADA4830-1
and ADA4830-2 is with the use of a R-C shunt circuit or a snubber
circuit. This method acts to resistively load the amplifier output,
thus reducing frequency response peaking. One drawback to this
approach is a slight loss of signal bandwidth. Figure 37 shows a
simple circuit representation of the implementation of the R-C
snubber circuit with R
SNT
and C
SNT
. Figure 38 shows the effects of
a R-C snubber circuit driving 47 pF, where R
SNT
= 73.2 Ω and C
SNT
= 0.1 µF.
ADA4830-1
+
–
C
L
= 47pF
C
SNT
= 0.1uF
R
L
= 1kΩ
R
SNT
= 73.2Ω
10020-053
Figure 37. R-C Test Circuit
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 50 100 150 200 250
V
OUT
(V)
TIME (ns)
10020-137
+V
S
= 5V
R
L
= 1kΩ
C
L
= 47pF
NO SNUBBER
CIRCUIT
R
SNT
= 73.2Ω
C
SNT
= 0.1µF
Figure 38. Pulse Response With and Without R-C Snubber Circuit
ADA4830-1/ADA4830-2 Data Sheet
Rev. C | Page 18 of 22
TYPICAL APPLICATIONS CIRCUITS
INN
VOUT
TO VIDEO
DECODER
GND
INP
VREF
ADA4830-1
75Ω
−
+
75Ω
POSITIVE WIRE
NEGATIVE WIRE
DRIVER PCB
+
STBENA +VS
SINGLE ENDED
AMPLIFIER
4.7µF
0.1µF
+VS
ENABLE
(INPUT)
STB FLAG
(OUTPUT)
2.2µF
0.1µF
+V
S
(2.9V TO 5.5V)
5kΩ
×1
10020-038
Figure 39. Typical Application with Pseudo Differential Input
INN
VOUT
TO VIDEO
DECODER
GND
INP
ADA4830-1
75Ω
−
+
37.5Ω
37.5Ω
DRIVER PCB
STBENA +VS
4.7µF
0.1µF
+VS
+
ENABLE
(INPUT)
STB FLAG
(OUTPUT)
2.2µF
0.1µF
5kΩ
×1
+V
S
(2.9V TO 5.5V)
VREF
DIFFERENTIAL
AMPLIFIER
10020-039
Figure 40. Typical Application with Fully Differential Input
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22

ADA4830-2BCPZ-R7

Mfr. #:
Buy ADA4830-2BCPZ-R7
Manufacturer:
Analog Devices Inc.
Description:
Differential Amplifiers High Spd w/ Input Short-Batt Protect
Lifecycle:
New from this manufacturer.
Delivery:
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