Data Sheet
Single-Supply, High Speed, Fixed G = +2,
Rail-to-Rail Output Video Amplifier
ADA4856-3
FEATURES
Voltage feedback architecture
Rail-to-rail output swing: 0.1 V to 4.9 V
High speed amplifier
−3 dB bandwidth: 225 MHz
0.1 dB flatness at 2 V p-p: 74 MHz
Slew rate: 800 V/μs
Settling time to 0.1% with 2 V step: 5 ns
High input common-mode voltage range
−VS − 0.2 V to +VS − 1 V
Supply range: 3 V to 5.5 V
Differential gain error: 0.01%
Differential phase error: 0.01°
Low power
7.8 mA/amplifier typical supply current
Power-down feature
Available in 16-lead LFCSP
+IN1
–IN1
OUT1
–VS
CONNECTION DIAGRAM
16
15
14
13
12 +VS
NC 1
11 OUT2
+IN2 2
ADA4856-3
9
7
8
NOTES
1. NC = NO CONNECT.
2. EXPOSED PAD CONNECTED TO –VS.
07686-001
6
+VS
–VS
5
OUT3
PD 4
–IN3
10 –IN2
+IN3
NC 3
Figure 1.
APPLICATIONS
Professional video
Consumer video
Imaging
Instrumentation
Base stations
Active filters
Buffers
7
The ADA4856-3 (triple) is a fixed gain of +2, single-supply, railto-rail output video amplifier. It provides excellent video
performance with 225 MHz, −3 dB bandwidth, 800 V/μs slew rate,
and 74 MHz, 0.1 dB flatness into a 150 Ω load. It has a wide
input common-mode voltage range that extends 0.2 V below
ground and 1 V below the positive rail. In addition, the output
voltage swings within 200 mV of either supply, making this video
amplifier easy to use on single-supply voltages as low as 3.3 V.
6
The ADA4856-3 is available in a 16-lead LFCSP and is designed
to work over the extended industrial temperature range of
−40°C to +105°C.
Rev. B
VS = 5V, VOUT = 1.4V p-p
VS = 3.3V, VOUT = 1.4V p-p
VS = 3.3V, VOUT = 2V p-p
5
VS = 5V, VOUT = 2V p-p
4
3
2
1
07686-058
The ADA4856-3 offers a typical low power of 7.8 mA per amplifier,
while being capable of delivering up to 52 mA of load current.
It also features a power-down function for power sensitive
applications that reduces the supply current to 1 mA.
CLOSED-LOOP GAIN (dB)
GENERAL DESCRIPTION
RL = 150Ω
0
1
10
100
FREQUENCY (MHz)
1000
Figure 2. Large Signal Frequency Response
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Technical Support
www.analog.com
ADA4856-3
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Theory of Operation ...................................................................... 12
Applications ....................................................................................... 1
Applications Information .............................................................. 13
Connection Diagram ....................................................................... 1
Using the ADA4856-3 in Gains Equal to +1, −1........................ 13
General Description ......................................................................... 1
Using the ADA4856-3 in Gains Equal to +3, +4, and +5 ..... 14
Revision History ............................................................................... 2
20 MHz Active Low-Pass Filter ................................................ 15
Specifications..................................................................................... 3
Video Line Driver ....................................................................... 15
5 V Operation ............................................................................... 3
Single-Supply Operation ........................................................... 16
3.3 V Operation ............................................................................ 4
Power Down ................................................................................ 16
Absolute Maximum Ratings ............................................................ 5
Layout Considerations ............................................................... 16
Thermal Resistance ...................................................................... 5
Power Supply Bypassing ............................................................ 16
Maximum Power Dissipation ..................................................... 5
Outline Dimensions ....................................................................... 17
ESD Caution .................................................................................. 5
Ordering Guide .......................................................................... 17
Pin Configuration and Function Descriptions ............................. 6
Typical Performance Characteristics ............................................. 7
REVISION HISTORY
3/13—Rev. A to Rev. B
Changed Package from CP-16-14 to CP-16-23 (Throughout) .... 1
Updated Outline Dimensions ........................................................17
Changes to Ordering Guide ............................................................. 7
1/09—Rev. 0 to Rev. A
Changes to Figure 9 ........................................................................... 7
Changes to Figure 13, Figure 15, and Figure 16 ............................ 8
Added Figure 17 and Figure 20; Renumbered Sequentially ........ 9
10/08—Revision 0: Initial Version
Rev. B | Page 2 of 20
Data Sheet
ADA4856-3
SPECIFICATIONS
5 V OPERATION
TA = 25°C, +VS = 5 V, −VS = 0 V, G = +2, RL = 150 Ω to midsupply, unless otherwise noted.
Table 1.
Parameter
DYNAMIC PERFORMANCE
−3 dB Bandwidth
Bandwidth for 0.1 dB Flatness
Slew Rate
Settling Time to 0.1% (Rise/Fall)
NOISE/DISTORTION PERFORMANCE
Harmonic Distortion (HD2/HD3)
Crosstalk, Output to Output
Input Voltage Noise
Input Current Noise
Differential Gain Error
Differential Phase Error
DC PERFORMANCE
Input Offset Voltage
Input Offset Voltage Drift
Input Bias Current
Input Offset Current
Closed-Loop Gain
Open-Loop Gain
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
OUTPUT CHARACTERISTICS
Output Voltage Swing
Linear Output Current Per Amplifier
POWER-DOWN
Turn-On Time
Turn-Off Time
Input Bias Current
Turn-On Voltage
POWER SUPPLY
Operating Range
Quiescent Current per Amplifier
Supply Current When Disabled
Power Supply Rejection Ratio
Test Conditions
Min
Typ
Max
Unit
VO = 0.1 V p-p
VO = 1.4 V p-p
VO = 2 V p-p
VO = 1.4 V p-p
VO = 2 V p-p
VO = 2 V step
VO = 2 V step
370
225
200
90
74
800
4.8/5.2
MHz
MHz
MHz
MHz
MHz
V/µs
ns
fC = 5 MHz, VO = 2 V p-p, RL = 1 kΩ
fC = 20 MHz, VO = 2 V p-p, RL = 1 kΩ
f = 5 MHz
f = 100 kHz
f = 100 kHz
−92/−110
−68/−71
−80
14
2
0.01
0.01
dBc
dBc
dB
nV/√Hz
pA/√Hz
%
Degrees
1.95
1.3
5.5
−3.8
±0.05
2
90
3.4
2.05
3.2
0.5
mV
µV/°C
µA
µA
V/V
dB
VCM = −0.2 V to +4 V
94
MΩ
pF
V
dB
HD2 ≤ −60 dBc, RL = 10 Ω
0.1 to 4.9
52
V
mA
78
950
0.2
−125
3.75
ns
ns
µA
µA
V
−VS − 0.2
Enabled
Powered down
+VS − 1
3
∆VS = 4.5 V to 5.5 V
Rev. B | Page 3 of 20
5.5
7.8
1.1
96
V
mA
mA
dB
ADA4856-3
Data Sheet
3.3 V OPERATION
TA = 25°C, +VS = 3.3 V, −VS = 0 V, G = +2, RL = 150 Ω to midsupply, unless otherwise noted.
Table 2.
Parameter
DYNAMIC PERFORMANCE
−3 dB Bandwidth
Bandwidth for 0.1 dB Flatness
Slew Rate
Settling Time to 0.1% (Rise/Fall)
NOISE/DISTORTION PERFORMANCE
Harmonic Distortion (HD2/HD3)
Crosstalk, Output to Output
Input Voltage Noise
Input Current Noise
Differential Gain Error
Differential Phase Error
DC PERFORMANCE
Input Offset Voltage
Input Offset Voltage Drift
Input Bias Current
Input Offset Current
Closed-Loop Gain
Open-Loop Gain
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
OUTPUT CHARACTERISTICS
Output Voltage Swing
Linear Output Current Per Amplifier
POWER-DOWN
Turn-On Time
Turn-Off Time
Turn-On Voltage
POWER SUPPLY
Operating Range
Quiescent Current per Amplifier
Quiescent Current When Powered Down
Power Supply Rejection Ratio
Test Conditions
Min
Typ
Max
Unit
VO = 0.1 V p-p
VO = 2 V p-p
VO = 2 V p-p
VO = 2 V step
VO = 2 V step
370
225
77
800
4.8/7
MHz
MHz
MHz
V/µs
ns
fC = 5 MHz, VO = 1 V p-p, RL = 1 kΩ
fC = 20 MHz, VO = 1 V p-p, RL = 1 kΩ
f = 5 MHz
f = 100 kHz
f = 100 kHz
−95/−128
−74/−101
−78
14
2
0.01
0.01
dBc
dBc
dB
nV/√Hz
pA/√Hz
%
Degrees
1.95
1.2
5.5
−3.8
±0.05
2
90
3
2.05
3.2
0.5
mV
µV/°C
µA
µA
V/V
dB
VCM = −0.2 V to +2.3 V
94
MΩ
pF
V
dB
HD2 ≤ −60 dBc, RL = 10 Ω
0.1 to 3.22
49
V
mA
78
950
2.05
ns
ns
V
−VS − 0.2
+VS − 1
3
∆VS = 2.97 V to 3.63 V
Rev. B | Page 4 of 20
5.5
7.5
0.98
94
V
mA
mA
dB
Data Sheet
ADA4856-3
ABSOLUTE MAXIMUM RATINGS
MAXIMUM POWER DISSIPATION
1
Rating
6V
See Figure 3
(−VS − 0.2 V) to (+VS − 1 V)
±VS
Observe power curves
−65°C to +125°C
−40°C to +105°C
300°C
Specification is for device in free air.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
The maximum power that can be safely dissipated by the
ADA4856-3 is limited by the associated rise in junction
temperature. The maximum safe junction temperature for
plastic encapsulated devices is determined by the glass transition
temperature of the plastic, approximately 150°C. Temporarily
exceeding this limit may cause a shift in parametric performance
due to a change in the stresses exerted on the die by the package.
Exceeding a junction temperature of 175°C for an extended
period can result in device failure.
To ensure proper operation, it is necessary to observe the
maximum power derating curves.
3.0
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, θJA is specified
for a device soldered in a circuit board for surface-mount packages.
2.5
2.0
1.5
1.0
0.5
07686-103
Parameter
Supply Voltage
Internal Power Dissipation1
Common-Mode Input Voltage
Differential Input Voltage
Output Short-Circuit Duration
Storage Temperature Range
Operating Temperature Range
Lead Temperature (Soldering, 10 sec)
MAXIMUM POWER DISSIPATION (W)
Table 3.
90
100
80
70
60
50
40
30
20
10
0
0
Unit
°C/W
–10
θJC
17.5
–20
θJA
67
–30
Package Type
16-Lead LFCSP
–40
Table 4.
AMBIENT TEMPERATURE (°C)
Figure 3. Maximum Power Dissipation vs. Ambient Temperature
ESD CAUTION
Rev. B | Page 5 of 20
ADA4856-3
Data Sheet
13 –VS
14 OUT1
16 +IN1
15 –IN1
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
NC 1
12 +VS
ADA4856-3
TOP VIEW
NC 3
11 OUT2
10 –IN2
9
+VS
–VS 8
OUT3 7
–IN3 6
+IN3 5
PD 4
NOTES
1. NC = NO CONNECT.
2. EXPOSED PAD CONNECTED TO –VS.
07686-003
+IN2 2
Figure 4. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17 (EPAD)
Mnemonic
NC
+IN2
NC
PD
+IN3
−IN3
OUT3
−VS
+VS
−IN2
OUT2
+VS
−VS
OUT1
−IN1
+IN1
Exposed Pad (EPAD)
Description
No Connect.
Noninverting Input 2.
No Connect.
Power Down.
Noninverting Input 3.
Inverting Input 3.
Output 3.
Negative Supply.
Positive Supply.
Inverting Input 2.
Output 2.
Positive Supply.
Negative Supply.
Output 1.
Inverting Input 1.
Noninverting Input 1.
The exposed pad must be connected to −VS.
Rev. B | Page 6 of 20
Data Sheet
ADA4856-3
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, +VS = 5 V, G = +2, RL = 150 Ω, large signal VOUT = 2 V p-p, small signal VOUT = 100 mV p-p, unless otherwise noted.
7
7
VS = 5V, VOUT = 1.4V p-p
VS = 3.3V
VS = 5V
4
3
2
0
100
10
FREQUENCY (MHz)
1
VS = 5V, VOUT = 2V p-p
4
3
2
1
07686-005
1
VS = 3.3V, VOUT = 2V p-p
5
07686-008
5
CLOSED-LOOP GAIN (dB)
CLOSED-LOOP GAIN (dB)
VS = 3.3V, VOUT = 1.4V p-p
6
6
0
1000
1
Figure 5. Small Signal Frequency Response vs. Supply Voltage
10
100
FREQUENCY (MHz)
1000
Figure 8. Large Signal Frequency Response vs. Supply Voltage
2
6.2
TA = +105°C
TA = +25°C
0
CLOSED-LOOP GAIN (dB)
CLOSED-LOOP GAIN (dB)
6.1
VS = 3.3V, VOUT = 1.4V p-p
VS = 5V, VOUT = 1.4V p-p
6.0
VS = 3.3V, VOUT = 2V p-p
VS = 5V, VOUT = 2V p-p
5.9
TA = –40°C
TA = +25°C
TA = +85°C
TA = +105°C
TA = –40°C
–2
TA = +85°C
–4
5.8
1
10
100
FREQUENCY (MHz)
07686-009
07686-006
–6
–8
1000
1
Figure 6. Large Signal 0.1 dB Flatness vs. Supply Voltage
10
100
FREQUENCY (MHz)
Figure 9. Small Signal Frequency Response vs. Temperature
7
CL = 4.4pF
6
RL = 150Ω
5
4
3
2
0
1
10
100
FREQUENCY (MHz)
CL = 2.2pF
4
2
0
–2
–4
07686-007
1
CL = 6.6pF
07686-010
CLOSED-LOOP GAIN (dB)
CLOSED-LOOP GAIN (dB)
RL = 1kΩ
6
1000
–6
1
1000
10
100
1000
FREQUENCY (MHz)
Figure 7. Small Signal Frequency Response vs. Load Resistance
Figure 10. Small Signal Frequency Response vs. Capacitive Load
Rev. B | Page 7 of 20
ADA4856-3
Data Sheet
–50
–50
RL = 1kΩ
VOUT = 2V p-p
–60
–70
DISTORTION (dBc)
–70
DISTORTION (dBc)
RL = 1kΩ
VOUT = 1V p-p
VS = 3.3V
–60
–80
–90
HD3
–100
HD2
–110
–80
–90
–100
HD3
–110
–130
–130
07686-011
–120
–140
0.1
1
10
FREQUENCY (MHz)
07686-014
HD2
–120
–140
0.1
100
Figure 11. Harmonic Distortion vs. Frequency
1
10
FREQUENCY (MHz)
100
Figure 14. Harmonic Distortion vs. Frequency
0
–10
–20
–40
OUT3
–60
OUT1
–80
OUT2
07686-012
–100
–120
0.1
1
10
100
–30
IN1, IN3, OUT2
–40
–50
–60
–70
IN1, IN2, OUT3
–80
IN2, IN3, OUT1
–90
–100
07686-015
ALL HOSTILE CROSSTALK (dB)
FORWARD ISOLATION (dB)
–20
–110
–120
1000
1
10
FREQUENCY (MHz)
FREQUENCY (MHz)
0.5
–10
0.4
–20
0.3
–30
0.2
SETTLING TIME (%)
0
–40
–50
+PSRR
–PSRR
–60
–70
–80
INPUT
OUTPUT
0.1
0
ERROR
–0.1
–0.2
0.1
1
10
100
07685-024
–0.3
–90
–100
0.01
500
Figure 15. Crosstalk vs. Frequency
07686-013
PSRR (dB)
Figure 12. Forward Isolation vs. Frequency
100
–0.4
–0.5
600
TIME (2ns/DIV)
FREQUENCY (MHz)
Figure 13. Power Supply Rejection Ratio (PSRR) vs. Frequency
Figure 16. Settling Time
Rev. B | Page 8 of 20
Data Sheet
ADA4856-3
100
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
1
10
1k
10k
1M
100k
FREQUENCY (Hz)
Figure 17. Output Voltage Noise vs. Frequency
Figure 20. Output Current Noise vs. Frequency
0.06
1.5
VS = 5V
VS = 3.3V
VS = 5V
VS = 3.3V
1.0
OUTPUT VOLTAGE (V)
0.04
OUTPUT VOLTAGE (V)
100
0.02
0
–0.02
–0.04
0.5
0
–0.5
07686-018
–1.0
–0.06
07686-021
10
10
07686-120
CURRENT NOISE (pA/√Hz)
100
07686-117
VOLTAGE NOISE (nV/√Hz)
1k
–1.5
TIME (10ns/DIV)
TIME (10ns/DIV)
Figure 18. Small Signal Transient Response vs. Supply Voltage
Figure 21. Large Signal Transient Response vs. Supply Voltage
0.08
1.5
0.06
OUTPUT VOLTAGE (V)
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0.02
0
–0.02
0.5
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0
–0.5
–0.04
–0.08
07686-022
–1.0
–0.06
07686-019
OUTPUT VOLTAGE (V)
1.0
0.04
–1.5
TIME (10ns/DIV)
TIME (10ns/DIV)
Figure 19. Small Signal Transient Response vs. Capacitive Load
Figure 22. Large Signal Transient Response vs. Capacitive Load
Rev. B | Page 9 of 20
ADA4856-3
Data Sheet
0.08
1.5
0.06
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.0
0.04
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0.02
0
–0.02
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0.5
0
–0.5
–0.04
07686-023
VS = 3.3V
–0.08
07686-026
–1.0
–0.06
VS = 3.3V
–1.5
TIME (10ns/DIV)
TIME (10ns/DIV)
Figure 23. Small Signal Transient Response vs. Capacitive Load
Figure 26. Large Signal Transient Response vs. Capacitive Load
2.5
4
2 × VIN
3
2 × VIN
2.0
1.5
VOUT
VOUT
1.0
1
VOLTAGE (V)
VOLTAGE (V)
2
0
–1
0.5
0
–0.5
–1.0
–2
07686-025
–4
VS = 3.3V
–2.0
–2.5
TIME (50ns/DIV)
TIME (50ns/DIV)
Figure 24. Output Overdrive Recovery
Figure 27. Output Overdrive Recovery
3.0
23.6
VPD
QUIESCENT CURRENT (mA)
2.0
1.5
VOUT
1.0
0.5
0
–0.5
07686-056
VOLTAGE (V)
VS = 5V
23.4
–1.0
–1.5
TIME (1us/DIV)
23.2
23.0
22.8
22.6
VS = 3.3V
22.4
22.2
22.0
21.8
–40
–25
–10
5
20
35
50
65
80
95
TEMPERATURE (°C)
Figure 25. Turn-On/Turn-Off Time
Figure 28. Quiescent Current vs. Temperature
Rev. B | Page 10 of 20
110
125
07686-132
2.5
07686-028
–1.5
–3
Data Sheet
ADA4856-3
1.8
5.00
1.7
4.95
SATURATION VOLTAGE (mV)
1.5
1.4
1.3
1.2
1.1
0.9
0.8
–40
–20
0
20
40
60
80
100
4.85
4.80
4.75
4.70
4.65
07686-034
1.0
4.90
07686-038
OFFSET VOLTAGE (mV)
1.6
4.60
0.01
120
0.1
TEMPERATURE (°C)
1
10
100
LOAD CURRENT (mA)
Figure 29. Offset Drift vs. Temperature
Figure 31. Output Saturation Voltage vs. Load Current
100
25.0
QUIESCENT CURRENT (mA)
1
0.1
24.0
23.5
23.0
0.01
100k
1M
10M
FREQUENCY (Hz)
100M
07686-057
22.5
07686-135
OUTPUT IMPEDENCE (Ω)
24.5
10
22.0
2.7
1G
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
SUPPLY VOLTAGE (V)
Figure 30. Output Impedance vs. Frequency
Figure 32. Quiescent Current vs. Supply Voltage
Rev. B | Page 11 of 20
5.4
ADA4856-3
Data Sheet
THEORY OF OPERATION
Besides a novel input stage, the ADA4856-3 employs the Analog
Devices, Inc., patented rail-to-rail output stage. This output
stage makes an efficient use of the power supplies, allowing the
op amp to drive up to three video loads to within 300 mV from
both rails. In addition, this output stage provides the amplifier
with very fast overdrive characteristics, an important property
in video applications.
The ADA4856-3 comes in a 16-lead LFCSP that has an exposed
thermal pad for lower operating temperature. This pad is connected
internally to the negative rail. To avoid printed circuit board (PCB)
layout problems, the ADA4856-3 features a new pinout flow that
is optimized for video applications. As shown in Figure 4, the
feedback and gain resistors are on-chip, which minimizes the
number of components needed and improves the design layout.
The ADA4856-3 is fabricated in Analog Devices dielectrically
isolated eXtra Fast Complementary Bipolar 3 (XFCB3) process,
which results in the outstanding speed and dynamic range
displayed by the amplifier.
+VS
C1
Gm2
+IN
–IN
R
C
–VS
Figure 33. High Level Design Schematic
Rev. B | Page 12 of 20
OUT
Gm1
07686-147
The ADA4856-3 is a voltage feedback op amp that employs a
new input stage that achieves a high slew rate while maintaining
a wide common-mode input range. The input common-mode
range of the ADA4856-3 extends from 200 mV below the negative
rail to about 1 V from the positive rail. This feature makes the
ADA4856-3 ideal for low voltage single-supply applications. In
addition, this new input stage does not sacrifice noise performance
for slew rate. At 14 nV/√Hz, the ADA4856-3 is one of the
lowest noise rail-to-rail output video amplifiers in the market.
Data Sheet
ADA4856-3
APPLICATIONS INFORMATION
+VS
USING THE ADA4856-3 IN GAINS EQUAL TO +1, −1
10µF
The ADA4856-3 was designed to offer outstanding video
performance, simplify applications, and minimize board area.
0.1µF
The ADA4856-3 is a triple amplifier with on-chip feedback
and gain set resistors. The gain is fixed internally at G = +2. The
inclusion of the on-chip resistors not only simplifies the design of
the application but also eliminates six surface-mount resistors,
saving valuable board space and lowering assembly costs.
Whereas the ADA4856-3 has a fixed gain of G = +2, it can be
used in other gain configurations, such as G = −1 and G = +1.
RF
RG
VOUT
VIN
RT
0.1µF
07686-030
10µF
–VS
Unity-Gain Operation
Option 1
GAIN OF +1
Figure 35. Unity Gain of Option 2
There are two options for obtaining unity gain (G = +1). The
first is shown in Figure 34. In this configuration, the –IN input
pin is tied to the output (feedback is now provided with the two
internal 402 Ω resistors in parallel), and the input is applied to
the noninverting input. The noise gain for this configuration is 1.
Inverting Unity-Gain Operation
In this configuration, the noninverting input is tied to ground
and the input signal is applied to the inverting input. The noise
gain for this configuration is +2, see Figure 36.
+VS
+VS
10µF
10µF
0.1µF
0.1µF
VIN
VIN
RT
VOUT
RT
VOUT
0.1µF
10µF
–VS
–VS
GAIN OF –1
GAIN OF +1
Figure 36. Inverting Configuration (G = −1)
Figure 34. Unity Gain of Option 1
Another option exists for running the ADA4856-3 as a unitygain amplifier. In this configuration, the noise gain is +2, see
Figure 35. The frequency response and transient response for
this configuration closely match the gain of +2 plots because the
noise gains are equal. This method does have twice the noise gain
of Option 1; however, in applications that do not require low noise,
Option 2 offers less peaking and ringing. By tying the inputs
together, the net gain of the amplifier becomes 1. Equation 1 shows
the transfer characteristic for the schematic shown in Figure 35.
(1)
6
3
which simplifies to VOUT = VIN.
OPTION 1
G = +1
VS = 5V
RL = 100Ω
VOUT = 100mV p-p
G = –1
0
OPTION 2
G = +1
–3
–6
–9
07686-044
R RG
V IN F
R
G
Figure 37 shows the small signal frequency response for both
gain of +1 (Option 1 and Option 2) and gain of −1 configurations.
It is clear that G = +1, Option 2 has better flatness and no peaking
compared to Option 1.
MAGNITUDE (dB)
Option 2
RF
VOUT V IN
RG
10µF
07686-031
07686-032
0.1µF
–12
1
10
100
FREQUENCY (MHz)
Figure 37. G = +1 and G = −1
Rev. B | Page 13 of 20
1000
ADA4856-3
Data Sheet
USING THE ADA4856-3 IN GAINS EQUAL TO +3,
+4, AND +5
Depending on certain applications, it might be useful to have a
fixed gain amplifier that can provide various gains. The advantage
of having a fixed gain amplifier is the ease of layout, the reduced
number of components needed, and the matching of the gain
and feedback resistors.
As shown in Figure 41, the large signal frequency response
for G = +4 is also flat out to 65 MHz, and it has a bandwidth
of 180 MHz.
Gain of +5 Configuration
The gain of +5 is very similar to the G = +3 configuration but with
U2 set to a gain of −1, which ends up being added to twice the
output of U1 to generate VOUT with G = +5.
Gain of +3 Configuration
–VS
0.1µF
16
15
14
0.1µF
1
12
2
11
+VS
VIN
VOUT
ADA4856-3
3
10
PD 4
9
5
+VS
14
6
7
10µF
0.1µF
–VS
0.1µF
Figure 40. Gain of +5
12
+VS
VIN
2
Figure 41 shows the large signal frequency response of the three
closed-loop gain sets (+3, +4, and +5) with flatness that extends
to 65 MHz and a −3 dB bandwidth of 190 MHz.
VOUT
11
ADA4856-3
PD
3
10
4
9
10µF
0.1µF
13
1
+
8
07686-047
+
0.1µF
15
10µF
13
–VS
16
+
Figure 38 shows the ADA4856-3 used as an amplifier with a
fixed gain of +3. No external resistors are required, just a simple
trace connecting certain inputs and outputs. Connect VIN to U1,
which is set to a gain of +2, and U2, which is set to unity. U3 then
takes the output of U1 and gains it up by +2 and subtracts the
output of U2 to produce VOUT. As shown in Figure 41, the large
signal frequency response for G = +3 is flat out to 65 MHz, with a
bandwidth of 165 MHz, a 2 V p-p output voltage, and a 100 Ω load.
+VS
15
6
7
+
8
G = +4
12
10µF
G = +3
0.1µF
07686-045
–VS
Figure 38. Gain of +3
Gain of +4 Configuration
To get a gain of +4, set one amplifier to a gain of +1 and set the
other two amplifiers to a gain of +2. Figure 39 shows VIN going in
U2 at unity, then U1 takes the output of U2 and gains it by +2, and
then feeds it to U3, which also gains it by +2 to produce VOUT.
–VS
CLOSED-LOOP GAIN (dB)
9
0.1µF
6
3
0
–3
–6
–9
RL = 100Ω
VS = 5V
VOUT = 2V p-p
–12
–15
–18
1
+
0.1µF
16
15
14
12
2
11
+VS
VOUT
ADA4856-3
3
10
PD 4
9
5
6
7
+VS
+
8
10µF
0.1µF
07686-046
0.1µF
–VS
100
1000
Figure 41. Large Signal Frequency Response for All Three Gains
0.1µF
1
10
FREQUENCY (MHz)
10µF
13
VIN
G = +5
07686-048
5
Figure 39. Gain of +4
Rev. B | Page 14 of 20
Data Sheet
ADA4856-3
20 MHz ACTIVE LOW-PASS FILTER
VIDEO LINE DRIVER
The ADA4856-3 triple amplifier lends itself to higher order
active filters. Figure 42 shows a 20 MHz, 6-pole, Sallen-Key
low-pass filter.
The ADA4856-3 was designed to excel in video driver applications.
Figure 44 shows a typical schematic for a video driver operating
on bipolar supplies.
75Ω
VIN (R)
–
VIN
C1
33pF
OUT1
U1
OP AMP
+
R2
604Ω
75Ω
16
15
14
C2
22pF
VIN (G)
2
75Ω
–
+VS
75Ω
VOUT (G)
11
ADA4856-3
3
10
PD 4
9
+VS
OUT2
U2
OP AMP
+
R4
732Ω
C3
33pF
10µF
0.1µF
12
1
R3
113Ω
0.1µF
0.1µF
13
+
R1
93.1Ω
VOUT (R)
–VS
5
6
7
0.1µF
8
VIN (B)
C4
15pF
+
10µF
0.1µF
0.1µF
75Ω
75Ω
07686-051
–VS
VOUT (B)
Figure 44. Video Driver Schematic
U3
OP AMP
+
R6
475Ω
C5
47pF
OUT3
VOUT
C6
15pF
07686-049
R5
121Ω
In applications that require multiple video loads be driven
simultaneously, the ADA4856-3 can deliver. Figure 45 shows
the ADA4856-3 configured with triple video loads. Figure 46
shows the triple video load performance.
+VS
Figure 42. 20 MHz, 6-Pole Low-Pass Filter
The filter has a gain of approximately 18 dB, which is set by
three fixed gain of 2 stages, and a flat frequency response out to
14 MHz. This type of filter is commonly used at the output of a
video DAC as a reconstruction filter. The frequency response of
the filter is shown in Figure 43.
ADA4856-3
0.1µF
10
FOUR POLES
TWO POLES
0
–VS
VOUT2
75Ω
0.1µF
+
75Ω
SIX POLES
75Ω
75Ω CABLE
10µF
VOUT3
75Ω
Figure 45. Video Driver Schematic for Triple Video Loads
6.5
–10
6.0
–20
RL = 150Ω
RL = 75Ω
RL = 50Ω
5.5
–40
–50
–60
1
10
100
200
5.0
4.5
4.0
3.5
FREQUENCY (MHz)
Figure 43. 20 MHz, Low-Pass Filter Frequency Response
VS = 5V
VOUT = 1V p-p
3.0
07686-053
MAGNITUDE (dB)
–30
07686-050
MAGNITUDE (dB)
75Ω
75Ω CABLE
–
75Ω
CABLE
VOUT1
75Ω
0.1µF
VIN
20
75Ω
75Ω CABLE
10µF
07686-052
–
2.5
1
10
100
200
FREQUENCY (MHz)
Figure 46. Large Signal Frequency Response for Various Loads
Rev. B | Page 15 of 20
ADA4856-3
Data Sheet
SINGLE-SUPPLY OPERATION
POWER DOWN
The ADA4856-3 can operate in single-supply applications.
Figure 47 shows the schematic for a single 5 V supply video
driver. Resistors R2 and R4 establish the midsupply reference.
Capacitor C2 is the bypass capacitor for the midsupply reference.
Capacitor C1 is the input coupling capacitor, and C6 is the output
coupling capacitor. Capacitor C5 prevents constant current from
being drawn through the internal gain set resistor. Resistor R3
sets the ac input impedance of the circuit.
The ADA4856-3 is equipped with a PD (power-down) pin for
all three amplifiers. This allows the user to reduce the quiescent
supply current when an amplifier is inactive. The power-down
threshold levels are derived from the voltage applied to the +VS
pin. When used in single-supply applications, this is especially
useful with conventional logic levels. The amplifier is enabled
when the voltage applied to the PD pin is greater than +VS − 1.25 V.
In a 5 V single-supply application, the typical threshold voltage
is +3.75 V, and in a 3.3 V dual-supply application, the typical
threshold voltage is +2 V. The amplifier is also enabled when the
PD pin is left floating (not connected). However, the amplifier is
powered down when the voltage on the PD pin is lower than 2.5 V
from +VS. If the PD pin is not used, it is best to connect it to the
positive supply
For more information on single-supply operation of op amps,
see “Avoiding Op-Amp Instability Problems In Single-Supply
Applications”, Analog Dialogue, Volume 35, Number 2, MarchMay, 2001, at www.analog.com.
+5V
R2
50kΩ
+5V
C2
1µF
C3
2.2µF
R4
50kΩ
C4
0.01µF
R3
1kΩ
Table 6. Power-Down Voltage Control
C6
220µF
VIN
C1
22µF
R1
50Ω
R5
75Ω
07686-035
Figure 47. AC-Coupled, Single-Supply Video Driver Schematic
In addition, the ADA4856-3 can be configured in dc-coupled,
single-supply operation. The common-mode input voltage
can go about 200 mV below ground, which makes it a true singlesupply part. However, in video applications, the black level is set
at 0 V, which means that the output of the amplifier must go to
the ground level as well. This part has a rail-to-rail output stage;
it can go as close as 100 mV from either rail. Figure 48 shows
the schematic for adding 50 mV dc offset to the input signal so
that the output is not clipped while still properly terminating
the input with 75 Ω.
5V
5V
C2
0.1µF
R1
3.74kΩ
VIN
U1
R3
75Ω
–VS
VOUT
R4
75Ω
ADA4856-3
07686-156
R2
76.8Ω
±2.5 V
3.3 V
>3.75 V
1.25 V
2.05 V
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