ANALOG DEVICES ADA4891-3 Service Manual

Rail-to-Rail Amplifiers

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

Rev. D

rights of third parties that may result from its use. Specifications subject to change without notice. No

Trademarks and registered trademarks are the prop erty of their respective owner s.

Fax: [phone] ©2010–2012 Analog Devices, Inc. All rights reserved.

08054-026

NC

1

–IN

2

+IN

3

–V

S

4

NC

8

+V

S

7

OUT

6

NC

5

ADA4891-1

NC = NO CONNECT

08054-001

OUT

1

+IN

3

–V

S

2

+V

S

5

–IN

4

ADA4891-1

08054-027

ADA4891-2

OUT1

1

–IN1

2

+IN1

3

–V

S

4

+V

S

8

OUT2

7

–IN2

6

+IN2

5

NC = NO CONNECT

PD1

1

OUT2

14

PD2

2

–IN2

13

PD3

3

+IN2

12

+V

S

4

–V

S

11

+IN1

5

+IN3

10

–IN1

6

–IN3

9

OUT1

7

OUT3

8

08054-073

ADA4891-3

+V

S

+IN2

OUT2

OUT4

+IN4
–V

S

+IN3

OUT3

+IN1

OUT1

1
2
3
4
5
6
7

14
13

12
11
10

9
8

–IN1

–IN2

–IN4

–IN3

08054-074

ADA4891-4

Data Sheet

FEATURES

Qualified for automotive applications (ADA4891-1W,

ADA4891-2W only)

High speed and fast settling

−3 dB bandwidth: 220 MHz (G = +1)
Slew rate: 170 V/µs
Settling time to 0.1%: 28 ns

Video specifications (G = +2, R

0.1 dB gain flatness: 25 MHz
Differential gain error: 0.05%
Differential phase error: 0.25°

Single-supply operation

Wide supply range: 2.7 V to 5.5 V

Output swings to within 50 mV of supply rails
Low distortion: 79 dBc SFDR at 1 MHz
Linear output current: 125 mA at −40 dBc
Low power: 4.4 mA per amplifier

APPLICATIONS

Automotive infotainment systems
Automotive driver assistance systems
Imaging
Consumer video
Active filters
Coaxial cable drivers
Clock buffers
Photodiode preamp
Contact image sensor and buffers

= 150 Ω)

L

Low Cost CMOS, High Speed,

CONNECTION DIAGRAMS

Figure 1. 8-Lead SOIC_N (R-8)

Figure 2. 5-Lead SOT-23 (RJ-5)

Figure 3. 8-Lead SOIC_N (R-8) and 8-Lead MSOP (RM-8)

GENERAL DESCRIPTION

The ADA4891-1 (single), ADA4891-2 (dual), ADA4891-3 (triple),
and ADA4891-4 (quad) are CMOS, high speed amplifiers that
offer high performance at a low cost. The amplifiers feature true
single-supply capability, with an input voltage range that extends
300 mV below the negative rail.

In spite of their low cost, the ADA4891 family provides high
performance and versatility. The rail-to-rail output stage enables
the output to swing to within 50 mV of each rail, enabling maxi­mum dynamic range.

The ADA4891 family of amplifiers is ideal for imaging applica­tions, such as consumer video, CCD buffers, and contact image
sensor and buffers. Low distortion and fast settling time also
make them ideal for active filter applications.

The ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 are avail­able in a wide variety of packages. The ADA4891-1 is available
in 8-lead SOIC and 5-lead SOT-23 packages. The ADA4891-2
is available in 8-lead SOIC and 8-lead MSOP packages. The
ADA4891-3 and ADA4891-4 are available in 14-lead SOIC and

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Figure 4. 14-Lead SOIC_N (R-14) and 14-Lead TSSOP (RU-14)

Figure 5. 14-Lead SOIC_N (R-14) and 14-Lead TSSOP (RU-14)

14-lead TSSOP packages. The amplifiers are specified to operate
over the extended temperature range of −40°C to +125°C.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

General Description ......................................................................... 1

Connection Diagrams ...................................................................... 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

5 V Operation ............................................................................... 3

3 V Operation ............................................................................... 4

Absolute Maximum Ratings ............................................................ 6

Maximum Power Dissipation ..................................................... 6

ESD Caution .................................................................................. 6

Typical Performance Characteristics ............................................. 7

Applications Information .............................................................. 15

Using the ADA4891 ................................................................... 15

Wideband, Noninverting Gain Operation .............................. 15

Wideband, Inverting Gain Operation ..................................... 15

Recommended Values ................................................................ 15

Effect of RF on 0.1 dB Gain Flatness ........................................ 16

Driving Capacitive Loads .......................................................... 17

Terminating Unused Amplifiers .............................................. 18

Disable Feature (ADA4891-3 Only) ........................................ 18

Single-Supply Operation ........................................................... 18

Video Reconstruction Filter ...................................................... 19

Multiplexer .................................................................................. 19

Layout, Grounding, and Bypassing .............................................. 20

Power Supply Bypassing ............................................................ 20

Grounding ................................................................................... 20

Input and Output Capacitance ................................................. 20

Input-to-Output Coupling ........................................................ 20

Leakage Currents ........................................................................ 20

Outline Dimensions ....................................................................... 21

Ordering Guide .......................................................................... 23

Automotive Products ................................................................. 23

REVISION HISTORY

3/12—Rev. C t o R e v. D

Added ADA4891-1W and ADA4891-2W ...................... Universal

Changes to Features Section and Applications Section ............... 1

Changes to Input Offset Voltage, Input Bias Current, and Open-

Loop Gain Parameters, Table 1 ....................................................... 4

Changes to Input Offset Voltage, Input Bias Current, and Open-

Loop Gain Parameters, Table 2 ....................................................... 5

Changes to Ordering Guide .......................................................... 23

Added Automotive Products Section .......................................... 23

9/10—Rev. B t o R e v. C

Changes to Figure 23 and Figure 24 ............................................... 9

7/10—Rev. A to Rev. B

Added ADA4891-3 and ADA4891-4 ............................... Universal

Added 14-Lead SOIC and 14-Lead TSSOP Packages .... Universal

Deleted Figure 4; Renumbered Figures Sequentially ................... 1

Changes to Features Section and General Description Section . 1

Added Figure 4 and Figure 5 ........................................................... 1

Changes to Table 1 ............................................................................ 3

Changes to Table 2 ............................................................................ 4

Changes to Maximum Power Dissipation Section

and Figure 6 ....................................................................................... 6

Added Table 4; Renumbered Tables Sequentially ......................... 6

Deleted Figure 11 ............................................................................... 6

Changes to Typical Performance Characteristics Section ........... 7

Deleted Figure 12 ............................................................................... 7

Changes to Wideband, Noninverting Gain Operation Section,

Wideband, Inverting Gain Operation Section, and Table 5 ..... 15

Added Table 6 ................................................................................. 16

Changes to Figure 52 ...................................................................... 16

Added Figure 53 ............................................................................. 16

Changed Layout of Driving Capacitive Loads Section .............. 17

Added Disable Feature (ADA4891-3 Only) Section

and Single-Supply Operation Section .......................................... 18

Added Multiplexer Section ........................................................... 19

Updated Outline Dimensions ....................................................... 21

Changes to Ordering Guide .......................................................... 23

6/10—Rev. 0 to R e v. A

Changes to Figure 26 ......................................................................... 9

Changes to Figure 33 and Figure 34............................................. 10

Updated Outline Dimensions ....................................................... 18

Changes to Ordering Guide .......................................................... 18

2/10—Revision 0: Initial Version

Rev. D | Page 2 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

Bandwidth for 0.1 dB Gain Flatness

25 MHz

Harmonic Distortion, HD2/HD3

fC = 1 MHz, VO = 2 V p-p, G = +1

−79/−93

dBc

ADA4891-1W/ADA4891-2W only, T

to T

,

66

dB

INPUT CHARACTERISTICS

RL = 150 Ω to 2.5 V

0.08 to 4.90

V

SPECIFICATIONS

5 V OPERATION

TA = 25°C, VS = 5 V, RL = 1 kΩ to 2.5 V, unless otherwise noted. All specifications are for the ADA4891-1, ADA4891-2, ADA4891-3, and
ADA4891-4, unless otherwise noted. For the ADA4891-1 and ADA4891-2, R
unless otherwise noted.

Table 1.

Parameter Test Conditions/Comments Min Typ Max Unit

DYNAMIC PERFORMANCE

−3 dB Small-Signal Bandwidth ADA4891-1/ADA4891-2, G = +1, VO = 0.2 V p-p 240 MHz

ADA4891-3/ADA4891-4, G = +1, VO = 0.2 V p-p 220 MHz

ADA4891-1/ADA4891-2, G = +2, V

= 150 Ω to 2.5 V

R

L

ADA4891-3/ADA4891-4, G = +2, V
R

= 150 Ω to 2.5 V

L

ADA4891-1/ADA4891-2, G = +2, VO = 2 V p-p,

= 150 Ω to 2.5 V, RF = 604 Ω

R

L

ADA4891-3/ADA4891-4, G = +2, V

= 150 Ω to 2.5 V, RF = 374 Ω

R

L

Slew Rate, tR/tF G = +2, VO = 2 V step, 10% to 90% 170/210 V/µs

−3 dB Large-Signal Frequency Response G = +2, VO = 2 V p-p, RL = 150 Ω 40 MHz

Settling Time to 0.1% G = +2, VO = 2 V step 28 ns

NOISE/DISTORTION PERFORMANCE

= 604 Ω; for the ADA4891-3 and ADA4891-4, RF = 453 Ω,

F

= 0.2 V p-p,

O

= 0.2 V p-p,

O

= 2 V p-p,

O

90 MHz

96 MHz

25 MHz

fC = 1 MHz, VO = 2 V p-p, G = −1 −75/−91 dBc

Input Voltage Noise f = 1 MHz 9 nV/√Hz

Differential Gain Error (NTSC) G = +2, RL = 150 Ω to 2.5 V 0.05 %

Differential Phase Error (NTSC) G = +2, RL = 150 Ω to 2.5 V 0.25 Degrees

All-Hostile Crosstalk f = 5 MHz, G = +2, VO = 2 V p-p −80 dB

DC PERFORMANCE

Input Offset Voltage ±2.5 ±10 mV

ADA4891-1W/ADA4891-2W only, T

T

MIN

to T

±3.1 mV

MAX

MIN

to T

±3.1 ±16 mV

MAX

Offset Drift 6 µV/°C

Input Bias Current −50 +2 +50 pA

ADA4891-1W/ADA4891-2W only, T

MIN

to T

−50 +50 nA

MAX

Open-Loop Gain RL = 1 kΩ to 2.5 V 77 83 dB

MIN

MAX

RL = 1 kΩ to 2.5 V

RL = 150 Ω to 2.5 V 71 dB

Input Resistance 5 GΩ

Input Capacitance 3.2 pF

Input Common-Mode Voltage Range

−V
+V

S

S

− 0.3 to

− 0.8

V

Common-Mode Rejection Ratio (CMRR) VCM = 0 V to 3.0 V 88 dB

OUTPUT CHARACTERISTICS

Output Voltage Swing RL = 1 kΩ to 2.5 V 0.01 to 4.98 V

Output Current 1% THD with 1 MHz, VO = 2 V p-p 125 mA

Short-Circuit Current

Sourcing 205 mA
Sinking 307 mA

Rev. D | Page 3 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

POWER SUPPLY

Negative PSRR

+VS = 5 V, −VS = −0.25 V to 0 V

63 dB

DYNAMIC PERFORMANCE

Slew Rate, tR/tF

G = +2, VO = 2 V step, 10% to 90%

140/230

V/µs

NOISE/DISTORTION PERFORMANCE

Parameter Test Conditions/Comments Min Typ Max Unit

POWER-DOWN PINS (PD1, PD2, PD3)

Threshold Voltage, VTH 2.4 V
Bias Current Part enabled 65 nA
Part powered down −22 µA
Turn-On Time Part enabled, output rises to 90% of final value 166 ns
Turn-Off Time

Operating Range 2.7 5.5 V
Quiescent Current per Amplifier 4.4 mA
Supply Current When Powered Down ADA4891-3 only 0.8 mA
Power Supply Rejection Ratio (PSRR)

Positive PSRR +VS = 5 V to 5.25 V, −VS = 0 V 65 dB

OPERATING TEMPERATURE RANGE −40 +125 °C

3 V OPERATION

TA = 25°C, VS = 3 V, RL = 1 kΩ to 1. 5 V, unless otherwise noted. All specifications are for the ADA4891-1, ADA4891-2, ADA4891-3, and
ADA4891-4, unless otherwise noted. For the ADA4891-1 and ADA4891-2, R
unless otherwise noted.

ADA4891-3 only

Part powered down, output falls to 10% of final

49 ns

value

= 604 Ω; for the ADA4891-3 and ADA4891-4, RF = 453 Ω,

F

Table 2.

Parameter Test Conditions/Comments Min Typ Max Unit

−3 dB Small-Signal Bandwidth ADA4891-1/ADA4891-2, G = +1, VO = 0.2 V p-p 190 MHz
ADA4891-3/ADA4891-4, G = +1, VO = 0.2 V p-p 175 MHz

Bandwidth for 0.1 dB Gain Flatness

ADA4891-1/ADA4891-2, G = +2, V
R

= 150 Ω to 1.5 V

L

ADA4891-3/ADA4891-4, G = +2, V

= 150 Ω to 1.5 V

R

L

ADA4891-1/ADA4891-2, G = +2, V

= 150 Ω to 1.5 V, RF = 604 Ω

R

L

ADA4891-3/ADA4891-4, G = +2, V
R

= 150 Ω to 1.5 V, RF = 374 Ω

L

= 0.2 V p-p,

O

= 0.2 V p-p,

O

= 2 V p-p,

O

= 2 V p-p,

O

75 MHz

80 MHz

18 MHz

18 MHz

−3 dB Large-Signal Frequency Response G = +2, VO = 2 V p-p, RL = 150 Ω 40 MHz
Settling Time to 0.1% G = +2, VO = 2 V step 30 ns

Harmonic Distortion, HD2/HD3 fC = 1 MHz, VO = 2 V p-p, G = −1 −70/−89 dBc
Input Voltage Noise f = 1 MHz 9 nV/√Hz
Differential Gain Error (NTSC) G = +2, RL = 150 Ω to 0.5 V, +VS = 2 V, −VS = −1 V 0.23 %
Differential Phase Error (NTSC) G = +2, RL = 150 Ω to 0.5 V, +VS = 2 V, −VS = −1 V 0.77 Degrees
All-Hostile Crosstalk f = 5 MHz, G = +2 −80 dB

DC PERFORMANCE

Input Offset Voltage ±2.5 ±10 mV
ADA4891-1W/ADA4891-2W only, T
T

MIN

to T

±3.1 mV

MAX

MIN

to T

±3.1 ±16 mV

MAX

Offset Drift 6 µV/°C
Input Bias Current −50 +2 +50 pA
ADA4891-1W/ADA4891-2W only, T

MIN

to T

−50 +50 nA

MAX

Rev. D | Page 4 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

Input Common-Mode Voltage Range

−VS − 0.3 to

V

OUTPUT CHARACTERISTICS

Threshold Voltage, VTH

1.3 V

Supply Current When Powered Down

ADA4891-3 only

0.73 mA

Parameter Test Conditions/Comments Min Typ Max Unit

Open-Loop Gain RL = 1 kΩ to 1.5 V 72 76 dB

ADA4891-1W/ADA4891-2W only, T

= 1 kΩ to 1.5 V

R

L

MIN

to T

MAX

RL = 150 Ω to 1.5 V 65 dB

INPUT CHARACTERISTICS

Input Resistance 5 GΩ

Input Capacitance 3.2 pF

Common-Mode Rejection Ratio (CMRR) VCM = 0 V to 1.5 V 87 dB

Output Voltage Swing RL = 1 kΩ to 1.5 V 0.01 to 2.98 V

RL = 150 Ω to 1.5 V 0.07 to 2.87 V

Output Current 1% THD with 1 MHz, VO = 2 V p-p 37 mA

Short-Circuit Current

Sourcing 80 mA
Sinking 163 mA

POWER-DOWN PINS (PD1, PD2, PD3)

ADA4891-3 only

Bias Current Part enabled 48 nA

Part powered down −13 µA

Turn-On Time Part enabled, output rises to 90% of final value 185 ns

Turn-Off Time

Part powered down, output falls to 10% of final
value

POWER SUPPLY

Operating Range 2.7 5.5 V

Quiescent Current per Amplifier 3.5 mA

60 dB

,

+VS − 0.8

58 ns

Power Supply Rejection Ratio (PSRR)

Positive PSRR +VS = 3 V to 3.15 V, −VS = 0 V 76 dB
Negative PSRR +VS = 3 V, −VS = −0.15 V to 0 V 72 dB

OPERATING TEMPERATURE RANGE −40 +125 °C

Rev. D | Page 5 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

Input Voltage (Common Mode)

−VS − 0.5 V to +VS

0

0.5

1.0

2.0

1.5

–55 –35 –15 5 25 45 65 85 105 125

AMBIENT TEMPERATURE (°C)

MAXIMUM POWER DISSIPATION (W)

14-LEAD TSS OP

8-LEAD SOIC_N

14-LEAD SOIC_N

5-LEAD SOT-23

8-LEAD MSOP

T

J

= 150°C

08054-002

8-Lead MSOP

133

°C/W

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

Supply Voltage 6 V

Differential Input Voltage ±VS
Storage Temperature Range −65°C to +125°C
Operating Temperature Range −40°C to +125°C
Lead Temperature (Soldering, 10 sec) 300°C

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.

MAXIMUM POWER DISSIPATION

The maximum power that can be safely dissipated by the
ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 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 can
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.

The still-air thermal properties of the package (θ
temperature (T
(P

) can be used to determine the junction temperature of the die.

D

), and the total power dissipated in the package

A

The junction temperature can be calculated as

= TA + (PD × θJA) (1)

T

J

The power dissipated in the package (P

) is the sum of the

D

quiescent power dissipation and the power dissipated in the
package due to the load drive for all outputs. It can be calculated by

P

= (VT × IS) + (VS − V

D

OUT

) × (V

OUT/RL

where:

is the total supply rail.

V

T

I

is the quiescent current.

S

is the positive supply rail.

V

S

V

is the output of the amplifier.

OUT

is the output load of the amplifier.

R

L

JA

) (2)

), the ambient

To ensure proper operation, it is necessary to observe the maxi­mum power derating curves shown in Figure 6. These curves
are derived by setting T

= 150°C in Equation 1. Figure 6 shows

J

the maximum safe power dissipation in the package vs. the
ambient temperature on a JEDEC standard 4-layer board.

Figure 6. Maximum Power Dissipation vs. Ambient Temperature

Tabl e 4 lists the thermal resistance (θJA) for each ADA4891-1/
ADA4891-2/ADA4891-3/ADA4891-4 package.

Table 4.

Package Type θJA Unit

5-Lead SOT-23 146 °C/W
8-Lead SOIC_N 115 °C/W

14-Lead SOIC_N 162 °C/W
14-Lead TSSOP 108 °C/W

ESD CAUTION

Rev. D | Page 6 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

–10

–9

–8

–7

–6

–5

–4

–3

–2

–1

0

1

2

3

4

0.1 1 10 100 1k

NORMALIZED CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

VS = 5V
V

OUT

= 200mV p-p

R

F

= 604Ω

R

L

= 1kΩ

G = +10

G = +5

G = –1
OR +2

G = +1

08054-028

–15

–12

–9

–6

–3

0

3

6

0.1 1 10 100 1k

CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

G = +1
V

OUT

= 200mV p-p

RL = 1kΩ

VS = 2.7V

VS = 5V

08054-029

V

S

= 3V

–4

–3

–2

–1

0

1

2

3

4

5

0.1 1 10 100 1k

CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

VS = 5V
G = +1
V

OUT

= 200mV p-p

RL = 1kΩ

08054-030

+125°C

+85°C

+25°C

0°C

–40°C

5
4
3
2
1

0
–1
–2
–3
–4
–5
–6
–7
–8
–9

–10

0.1 1 10 100 1k
FREQUENCY (MHz)

NORMALIZED CLOSED-LOOP GAIN (dB)

08054-076

G = +10

G = +5

G = +1

G = –1 OR +2

VS = 5V
V

OUT

= 200mV p-p

R

F

= 453Ω

R

L

= 1kΩ

6

3

0

–3

–6

–9

–12

–15

0.1 1 10 100 1k
FREQUENCY (MHz)

CLOSED-LOOP GAIN (dB)

08054-077

V

S

= 2.7V

G = +1
V

OUT

= 200mV p-p

R

L

= 1kΩ

V

S

= 3V

V

S

= 5V

–4

–3

–2

–1

0

1

2

3

4

5

0.1 1 10 100 1k
FREQUENCY (MHz)

CLOSED-LOOP GAIN (dB)

08054-078

VS = 5V
G = +1
V

OUT

= 200mV p-p

RL = 1kΩ

+125°C

+85°C

+25°C

0°C

–40°C

TYPICAL PERFORMANCE CHARACTERISTICS

Unless otherwise noted, all plots are characterized for the ADA4891-1, ADA4891-2, ADA4891-3, and ADA4891-4. For the ADA4891-1
and ADA4891-2, the typical R

Figure 7. Small-Signal Frequency Response vs. Gain, VS = 5 V,

ADA4891-1/ADA4891-2

value is 604 Ω. For the ADA4891-3 and ADA4891-4, the typical RF value is 453 Ω.

F

Figure 10. Small-Signal Frequency Response vs. Gain, V

ADA4891-3/ADA4891-4

= 5 V,

S

Figure 8. Small-Signal Frequency Response vs. Supply Voltage,

ADA4891-1/ADA4891-2

Figure 9. Small-Signal Frequency Response vs. Temperature, VS = 5 V,

ADA4891-1/ADA4891-2

Figure 11. Small-Signal Frequency Response vs. Supply Voltage,

ADA4891-3/ADA4891-4

Figure 12. Small-Signal Frequency Response vs. Temperature, V

= 5 V,

S

ADA4891-3/ADA4891-4

Rev. D | Page 7 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

–6

–5

–4

–3

–2

–1

0

3

4

5

6

1

2

7

0.1 1 10 100 1k

+125°C

+25°C

0°C

–40°C

VS = 3V
G = +1
V

OUT

= 200mV p-p

RL = 1kΩ

08054-031

+85°C

–0.5

–0.4

–0.3

–0.2

–0.1

0

0.1

10.1 10 100

FREQUENCY (MHz)

NORMALIZED CLOSED-LOOP GAIN (dB)

G = +2
R

F

= 604Ω

RL = 150Ω

V

S

= 3V

V

OUT

= 2V p-p

VS = 5V

V

OUT

= 1.4V p-p

V

S

= 3V

V

OUT

= 1.4V p-p

08054-019

VS = 5V

V

OUT

= 2V p-p

–10

–9

–8

–7

–6

–5

–4

–3

–2

–1

0

1

0.1 1 10 100 1k

NORMALIZED CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

VS = 5V
R

L

= 150Ω

V

OUT

= 2V p-p

G = +1

R

F

= 0Ω

G = –1

RF = 604Ω

G = +2

R

F

= 604Ω

G = +5

R

F

= 604Ω

08054-036

CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

–6

–5

–4

–3

–2

–1

0

3

4

5

6

1

2

7

0.1 1 10 100 1k

VS = 3V
G = +1
V

OUT

= 200mV p-p

R

L

= 1kΩ

08054-079

+125°C

+85°C

+25°C

0°C

–40°C

0.1

0

–0.1

–0.2

–0.3

–0.4

–0.5

0.1 1 10 100
FREQUENCY (MHz)

NORMALIZED CLOSED-LOOP GAIN (dB)

08054-080

VS = 3V
V

OUT

= 1.4V p-p

V

S

= 3V

V

OUT

= 2V p-p

V

S

= 5V

V

OUT

= 2V p-p

G = +2
R

F

= 374Ω

R

L

= 150Ω

V

S

= 5V

V

OUT

= 1.4V p-p

1

0
–1
–2
–3
–4
–5
–6
–7
–8
–9

–10

0.1 1 10 100 1k
FREQUENCY (MHz)

NORMALIZED CLOSED-LOOP GAIN (dB)

08054-081

VS = 5V
R

L

= 150Ω

V

OUT

= 2V p-p

G = +1
R

F

= 0Ω

G = –1
R

F

= 453Ω

G = +5
R

F

= 453Ω

G = +2
R

F

= 453Ω

Figure 13. Small-Signal Frequency Response vs. Temperature, V

ADA4891-1/ADA4891-2

Figure 14. 0.1 dB Gain Flatness vs. Supply Voltage, G = +2,

ADA4891-1/ADA4891-2

= 3 V,

S

Figure 16. Small-Signal Frequency Response vs. Temperature, V

= 3 V,

S

ADA4891-3/ADA4891-4

Figure 17. 0.1 dB Gain Flatness vs. Supply Voltage, G = +2,

ADA4891-3/ADA4891-4

Figure 15. Large-Signal Frequency Response vs. Gain, VS = 5 V,

ADA4891-1/ADA4891-2

Figure 18. Large-Signal Frequency Response vs. Gain, V

= 5 V,

S

ADA4891-3/ADA4891-4

Rev. D | Page 8 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

–

–

–

–

1

0

–1

–2

–3

–4

–5

–6

–7

VS = 3V

–8

R

= 604Ω

F

NORMALIZE D CLOSED-LOOP GAIN ( dB)

R

= 150Ω

–9

L

–10

0.1 1 10 100 1k

G = +2
V

= 2V p-p

OUT

G = +5
V

= 2V p-p

OUT

FREQUENCY (MHz)

G = –1
V

OUT

G = +1
V

OUT

Figure 19. Large-Signal Frequency Response vs. Gain, V

ADA4891-1/ADA4891-2

40

VS = 5V
R

= 1kΩ

L

V

= 2V p-p

OUT

G = +1

SECOND HARMONIC

G = +1

THIRD HARMONIC

0.1 1 10

FREQUE NCY (MHz)

DISTORTION (dBc)

–50

–60

–70

–80

–90

–100

–110

–120

G = +2

SECOND HARMONIC

G = +2

THIRD HARMONIC

Figure 20. Harmonic Distortion (HD2, HD3) vs. Frequency, VS = 5 V

= 2V p-p

= 1V p-p

= 3 V,

S

1

0

–1

–2

–3

–4

–5

–6

–7

VS = 3V

–8

R

F

NORMALIZE D CLOSED-LOOP GAIN ( dB)

R

–9

L

–10

0.1 1 10 100 1k

08054-037

= 453Ω
= 150Ω

G = +2
V

= 2V p-p

OUT

G = +5
V

OUT

FREQUENCY (MHz)

= 2V p-p

Figure 22. Large-Signal Frequency Response vs. Gain, V

G = –1
V

OUT

G = +1
V

OUT

= 2V p-p

= 1V p-p

= 3 V,

S

08054-082

ADA4891-3/ADA4891-4

30

VS = 3V

= 1kΩ

R

L

= 2V p-p

V

OUT

–40

–50

G = +1

SECOND HARMO NIC

–60

–70

DISTORTION (d Bc)

–80

–90

0.1 1 10

08054-038

G = +2

THIRD HARMO NIC

G = +2

SECOND HARMONIC

FREQUENC Y (MHz)

G = +1

THIRD HARMO NIC

+V

= +1.9V

S

IN

50Ω

–V

S

1kΩ

= –1.1V

G = +1 CONFIGURAT ION

OUT

08054-039

Figure 23. Harmonic Distortion (HD2, HD3) vs. Frequency, VS = 3 V

40

VS = 5V
R

= 604Ω

F

–50

R

= 1kΩ

L

f

= 1MHz

C

–60

–70

–80

–90

DISTORT ION (dBc)

–100

–110

–120

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

G = –1

SECOND HARMONIC

G = +1

THIRD HARMONIC

OUTPUT VOLTAGE (V p-p)

G = +1

SECOND HARMONIC

G = –1

THIRD HARMONIC

Figure 21. Harmonic Distortion (HD2, HD3) vs. Output Voltage, VS = 5 V

8054-040

–50

–60

–70

40

= +1.9V

+V

S

IN

50Ω

–V

= –1.1V

S

G = +1
CONFIGURATION

SECOND HARMO NIC

OUT

1kΩ

G = +1

–80

DISTORTION (dBc)

–90

–100

–110

–120

0

SECOND HARMO NIC

G = –1

G = –1
THIRD HARMO NIC

G = +1
THIRD HARMO NIC

VS = 3V

f

= 1MHz

C

0.51.01.52.02.53.0

OUTPUT VOLTAGE (V p-p)

Figure 24. Harmonic Distortion (HD2, HD3) vs. Output Voltage, VS = 3 V

08054-041

Rev. D | Page 9 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

–

1k

–50

40

G = +2
R

= 604Ω

F

R

= 150Ω

L

f

= 1MHz

C

VS = 3V

SECOND HARMONIC

VS = 3V
THIRD HARMONIC

–60

–70

–80

DISTORT ION (dBc)

–90

–100

00.51.0

VS = 5V

SECOND HARMONIC

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5. 0

OUTPUT VOLTAGE (V p-p)

VS = 5V

THIRD HARMONIC

Figure 25. Harmonic Distortion (HD2, HD3) vs. Output Voltage, G = +2

90

80

70

60

50

40

30

20

OPEN-LOOP GAIN (dB)

10

0

–10

0.001 0.01 0.1 1 10 100 1k

PHASE

GAIN

FREQUE NCY (MHz)

VS = 5V
R

= 1kΩ

L

0

–18

–36

–54

–72

–90

–108

–126

–144

–162

–180

Figure 26. Open-Loop Gain and Phase vs. Frequency

08054-042

PHASE (Degrees)

100

10

VOLTAGE NOISE (nV/ Hz)

VS = 5V
G = +1

1

10 100

1k 10k 100k 1M 10M

FREQUENCY ( Hz)

08054-045

Figure 28. Input Voltage Noise vs. Frequency

0.06

0.04

0.02

0

–0.02

DIFFERENTIAL

DIFFERENTIAL

08054-043

VS = 5V, G = +2

–0.04

GAIN ERROR (%)

PHASE ERROR (Degrees)

= 604Ω, RL = 150Ω

R

F

–0.06

1ST2ND3RD4TH5TH6TH7TH8TH9TH10

0.3

0.2

0.1

0

–0.1

VS = 5V, G = +2

–0.2

= 604Ω, RL = 150Ω

R

F

–0.3

1ST2ND3RD4TH5TH6TH7TH8TH9TH10

MODULATING RAMP LEVEL (IRE)

TH

TH

08054-060

Figure 29. Differential Gain and Phase Errors

7

6

5

4

3

2

1

0

–1

VS = 5V

–2

G = +2

NORMALIZE D CLOSED-LOOP GAI N (dB)

R

= 150Ω

L

–3

V

= 200mV p-p

OUT

–4

0.1 1 10 100 1k

CL = 47pF

CL = 22pF

CL = 10pF

CL = 0pF

FREQUENCY (MHz)

Figure 27. Small-Signal Frequency Response vs. C

ADA4891-1/ADA4891-2

08054-044

,

L

7

6

5

4

3

2

1

0

–1

VS = 5V

–2

G = +2

NORMALIZE D CLOSED-LOOP GAI N (dB)

= 150Ω

R

–3

L

= 200mV p-p

V

OUT

–4

0.1 1 10 100 1k

CL = 47pF

CL = 22pF

CL = 10pF

CL = 0pF

FREQUENCY (MHz)

Figure 30. Small-Signal Frequency Response vs. C

ADA4891-3/ADA4891-4

08054-083

,

L

Rev. D | Page 10 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

0.01

0.1

1

10

100

0.01 0.1 1 10 100

FREQUENCY (MHz)

V

S

= 5V

G = +1

OUTPUT IMPEDANCE (Ω)

08054-046

OUTPUT VOLTAGE (mV)

100

0

–100

G = +1
V

OUT

= 200mV p-p

RL = 1kΩ

V

S

= 3V

08054-048

VS = 5V

50mV/DIV 5ns/DIV

OUTPUT VOLTAGE (V)

1

0

–1

V

S

= 5V
G = +1
V

OUT

= 2V p-p

RL = 150Ω

RL = 1kΩ

08054-049

0.5V/DIV

5ns/DIV

100k

10k

1k

100

10

1

0.01 0.1 1 10 100

OUTPUT IMPEDANCE (Ω)

FREQUENCY (MHz)

08054-089

VS = 5V
G = +1

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

10 20 30 40 50 60 70 80 90

TIME (ns)

OUTPUT VOLTAGE (V)

08054-047

V

S

= 5V

R

L

= 1kΩ

V

S

= 5V

R

L

= 150Ω

V

S

= 3V

R

L

= 150Ω

V

S

= 3V

RL = 1kΩ

G = +2
V

OUT

= 2V p-p

0.5

0

–0.5

OUTPUT VOLTAGE (V)

R

L

= 150Ω

RL = 1kΩ

VS = 3V
G = +1
V

OUT

= 1V p-p

08054-050

0.5V/DIV

5ns/DIV

Figure 31. Closed-Loop Output Impedance vs. Frequency, Part Enabled

Figure 32. Small-Signal Step Response, G = +1

Figure 34. Closed-Loop Output Impedance vs. Frequency, Part Disabled

(ADA4891-3 Only)

Figure 35. Large-Signal Step Response, G = +2

Figure 33. Large-Signal Step Response, V

= 5 V, G = +1

S

Figure 36. Large-Signal Step Response, V

= 3 V, G = +1

S

Rev. D | Page 11 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

A

0.30

0.20

0.10

VS=5V
G=+2

= 150Ω

R

L

V

OUT

=2Vp-p

200

190

180

VS = 5V
G = +2

= 150Ω

R

L

FALLING EDGE

0

SETTLING (%)

–0.10

–0.20

–0.30

02530

35 40 45

TIME (ns)

Figure 37. Short-Term Settling Time to 0.1%

3

INPUT

2

OUTPUT

1

AMPLITUDE ( V)

0

–1

Figure 38. Input Overdrive Recovery from Positive Rail

5ns/DIV1V/DIV

= ±2.5V

V

S

G = +1
R

= 1kΩ

L

TE (V/µs)

170

160

SLEW R

150

140

08054-061

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

RISING EDGE

OUTPUT STEP (V)

08054-051

Figure 40. Slew Rate vs. Output Step

1

VS = ±2.5V
G = +1

= 1kΩ

R

L

0

–1

AMPLITUDE (V)

–2

08054-071

–3

1V/DIV 5ns/DIV

INPUT

OUTPUT

08054-063

Figure 41. Input Overdrive Recovery from Negative Rail

3

OUTPUT

2

1

0

AMPLITUDE (V)

–1

–2

1V/DIV 5ns/DIV

–3

INPUT

Figure 39. Output Overdrive Recovery from Positive Rail

VS = ±2.5V
G = –2

= 1kΩ

R

L

08054-070

Rev. D | Page 12 of 24

3

INPUT

2

1

0

AMPLITUDE (V)

–1

–2

OUTPUT

1V/DIV 5ns/DIV

–3

Figure 42. Output Overdrive Recovery from Negative Rail

VS = ±2.5V
G = –2
R

= 1kΩ

L

08054-052

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

–10

–20

–30

–90

–80

–70

–60

–50

–40

0.01 0.1 1 10 100

CMRR (dB)

FREQUENCY (MHz)

08054-090

V

S

= 5V

–80

–70

–60

–50

–40

–30

–20

–10

0.01 0.1 1 10 100

PSRR (dB)

FREQUENCY (MHz)

+PSRR

–PSRR

Vs = 5V
G = +1

08054-054

08054-072

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

0.1 1 10 100 1k

CROSSTALK (dB)

FREQUENCY (MHz)

Vs = 5V
G = +2
R

L

= 1 kΩ

V

OUT

= 2V p-p

0
–10

–20

–30

–40

–50

–60
–70

–80
–90

–100

0.1 1 10 100

1k

FREQUENCY (MHz)

ISOLATION (dB)

08054-084

TSSOP

SOIC

V

S

= 5V
G = +2
R

L

= 150Ω

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 10 20 30 40 50 60 70 80 90 100

OUTPUT SATURATION VOLTAGE (V)

V

OH

, +125°C

V

OH

, +25°C

V

OH

, –40°C

V

OL

, +125°C

V

OL

, +25°C

V

OL

, –40°C

I

LOAD

(mA)

V

S

= 5V
G = –2
R

F

= 604Ω

08054-056

3.0

3.5

4.0

4.5

5.0

5.5

6.0

–40 –20 0 20 40 60 80 100 120

QUIESCENT SUPPLY CURRENT (mA)

V

S

= 5V

TEMPERATURE (ºC)

08054-057

Figure 43. CMRR vs. Frequency

Figure 44. PSRR vs. Frequency

Figure 46. Forward Isolation vs. Frequency (ADA4891-3 Only)

Figure 47. Output Saturation Voltage vs. Load Current and Temperature

Figure 45. All-Hostile Crosstalk (Output-to-Output) vs. Frequency

Figure 48. Supply Current per Amplifier vs. Temperature

Rev. D | Page 13 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8

QUIESCENT SUPPLY CURRENT (mA)

SUPPLY VOLTAGE (V)

08054-058

Figure 49. Supply Current per Amplifier vs. Supply Voltage

Rev. D | Page 14 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

08054-023

ADA4891

R

F

R

G

R

T

50Ω

SOURCE

R

L

+V

S

–V

S

10µF

0.1µF

V

I

V

O

10µF

0.1µF

08054-024

ADA4891

R

F

R

T

R

G

50Ω

SOURCE

R

L

+V

S

–V

S

V

I

V

O

10µF

0.1µF

10µF

0.1µF

+10

604

67.1

12.7

71

72

0

APPLICATIONS INFORMATION

USING THE ADA4891

Understanding the subtleties of the ADA4891 family of amplifiers
provides insight into how to extract the peak performance from
the device. The following sections describe the effect of gain,
component values, and parasitics on the performance of the
ADA4891. The wideband, noninverting gain configuration of
the ADA4891 is shown in Figure 50; the wideband, inverting
gain configuration of the ADA4891 is shown in Figure 51.

WIDEBAND, NONINVERTING GAIN OPERATION

WIDEBAND, INVERTING GAIN OPERATION

Figure 50. Noninverting Gain Configuration

In Figure 50, RF and RG denote the feedback and gain resistors,
respectively. Together, R
amplifier. The value of R
more information, see the Effect of R
section). Typical R
ADA4891-1/ADA4891-2. Typical R

and RG determine the noise gain of the

F

defines the 0.1 dB bandwidth (for

F

on 0.1 dB Gain Flatness

F

values range from 549 Ω to 698 Ω for the

F

values range from 301 Ω

F

to 453 Ω for the ADA4891-3/ADA4891-4.

In a controlled impedance signal path, R

is used as the input

T

termination resistor designed to match the input source imped­ance. Note that R

is not required for normal operation. RT is

T

generally set to match the input source impedance.

Figure 51. Inverting Gain Configuration

Figure 51 shows the inverting gain configuration. For the
inverting gain configuration, set the parallel combination of
R

and RG to match the input source impedance.

T

Note that a bias current cancellation resistor is not required in
the noninverting input of the amplifier because the input bias
current of the ADA4891 is very low (less than 2 pA). Therefore,
the dc errors caused by the bias current are negligible.

For both noninverting and inverting gain configurations, it is
often useful to increase the R
output. Increasing the R

value to decrease the load on the

F

value improves harmonic distortion at

F

the expense of reducing the 0.1 dB bandwidth of the amplifier.
This effect is discussed further in the Effect of R

on 0.1 dB Gain

F

Flatness section.

RECOMMENDED VALUES

Tabl e 5 and Tabl e 6 provide a quick reference for various configu­rations and show the effect of gain on the −3 dB small-signal
bandwidth, slew rate, and peaking of the ADA4891-1/ADA4891-2/
ADA4891-3/ADA4891-4. Note that as the gain increases, the
small-signal bandwidth decreases, as is expected from the gain
bandwidth product relationship. In addition, the phase margin
improves with higher gains, and the amplifier becomes more
stable. As a result, the peaking in the frequency response is
reduced (see Figure 7 and Figure 10).

Table 5. Recommended Component Values and Effect of Gain on ADA4891-1/ADA4891-2 Performance (R

= 1 kΩ)

L

Feedback Network Values −3 dB Small-Signal Bandwidth (MHz) Slew Rate (V/µs)

= 200 mV p-p tR tF

−1 604 604 118 188 192 1.3
+1 0 Open 240 154 263 2.6
[phone] 210 1.4

OUT

+5 604 151 32.5 149 154 0

Rev. D | Page 15 of 24

Peaking (dB) Gain RF (Ω) RG (Ω) V

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

–0.4

–0.3

–0.2

–0.1

0

0.1

0.2

10.1 10 100

FREQUENCY (MHz)

NORMALIZED CLOSED-LOOP GAIN (dB)

VS = 5V
G = +2
V

OUT

= 2V p-p

R

L

= 150Ω

RG = RF = 604Ω

RG = R

F

= 549Ω

RG = RF = 649Ω

RG = RF = 698Ω

08054-022

–0.4

–0.5

–0.3

–0.2

–0.1

0

0.1

0.2

0.3

10.1 10 100

FREQUENCY (MHz)

NORMALIZED CLOSED-LOOP GAIN (dB)

08054-085

V

S

= 5V
G = +2
V

OUT

= 2V p-p

R

L

= 150Ω

R

G

= R

F

= 453Ω

R

G

= R

F

= 402Ω

R

G

= R

F

= 357Ω

R

G

= R

F

= 301Ω

Table 6. Recommended Component Values and Effect of Gain on ADA4891-3/ADA4891-4 Performance (RL = 1 kΩ)

Feedback Network Values −3 dB Small-Signal Bandwidth (MHz) Slew Rate (V/µs)
Gain RF (Ω) RG (Ω) V

−1 453 453 97 186 194 0.9
+1 0 Open 220 151 262 4.1
[phone] 0.9
+5 453 90.6 31 112 120 0
+10 453 45.3 13 68 67 0

EFFECT OF RF ON 0.1 dB GAIN FLATNESS

Gain flatness is an important specification in video applications.
It represents the maximum allowable deviation in the signal
amplitude within the pass band. Tests have revealed that the
human eye is unable to distinguish brightness variations of
less than 1%, which translates into a 0.1 dB signal drop within
the pass band or, put simply, 0.1 dB gain flatness.

The PCB layout configuration and bond pads of the chip often
contribute to stray capacitance. The stray capacitance at the
inverting input forms a pole with the feedback and gain resistors.
This additional pole adds phase shift and reduces phase margin
in the closed-loop phase response, causing instability in the
amplifier and peaking in the frequency response.

Figure 52 and Figure 53 show the effect of using various values
for Feedback Resistor R
Figure 52 shows the effect for the ADA4891-1/ADA4891-2.
Figure 53 show the effect for the ADA4891-3/ADA4891-4.
Note that a larger R
additional pole formed by R
shifts down in frequency and interacts significantly with the
internal poles of the amplifier.

Figure 52. 0.1 dB Gain Flatness, Noninverting Gain Configuration,

on the 0.1 dB gain flatness of the parts.

F

value causes more peaking because the

F

and the input stray capacitance

F

ADA4891-1/ADA4891-2

= 200 mV p-p tR tF

OUT

Figure 53. 0.1 dB Gain Flatness, Noninverting Gain Configuration,

To obtain the desired 0.1 dB bandwidth, adjust the feedback
resistor, R

, as shown in Figure 52 and Figure 53. If RF cannot

F

be adjusted, a small capacitor can be placed in parallel with R
to reduce peaking.

The feedback capacitor, C
resistor, which cancels out the pole formed by the input stray
capacitance and the gain and feedback resistors. For a first pass
in determining the C

× CS = RF × CF

R

G

F

where:

R

is the gain resistor.

G

C

is the input stray capacitance.

S

is the feedback resistor.

R

F

C

is the feedback capacitor.

F

Using this equation, the original closed-loop frequency response of
the amplifier is restored, as if there is no stray input capacitance.
Most often, however, the value of C

Figure 54 shows the effect of using various values for the
feedback capacitor to reduce peaking. In this case, the
ADA4891-1/ ADA4891-2 are used for demonstration purposes
and R

= RG = 604 Ω. The input stray capacitance, together with

F

the board parasitics, is approximately 2 pF.

Rev. D | Page 16 of 24

Peaking (dB)

ADA4891-3/ADA4891-4

, forms a zero with the feedback

F

value, use the following equation:

is determined empirically.

F

F

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

08054-025

–0.3

–0.2

–0.1

0

0.1

0.2

0.1 1 10 100

NORMALIZED CLOSED-LOOP GAIN (dB)

FREQUENCY (MHz)

C

F

= 3.3pF

C

F

= 0pF

C

F

= 1pF

V

S

= 5V
G = +2
R

F

= 604Ω

R

L

= 150Ω

V

OUT

= 2V p-p

–10

–8

–6

–4

–2

0

2

4

6

8

0.1 1 10 100

MAGNITUDE ( dB)

FREQUENCY (MHz)

VS = 5V
V

OUT

= 200mV p-p
G = +1
R

L

= 1kΩ

CL = 6.8pF

08054-032

OUTPUT VOLTAGE (mV)

50ns/DIV50mV/DIV

VS = 5V
G = +1
R

L

= 1kΩ

C

L

= 6.8pF

0

100

–100

08054-034

MAGNITUDE ( dB)

–10

–8

–6

–4

–2

0

2

4

6

8

0.1 1 10 100

FREQUENCY (MHz)

VS = 5V
V

OUT

= 200mV p-p
G = +1
R

L

= 1kΩ

CL = 6.8pF

RS = 0Ω

R

S

= 100Ω

50Ω

R

L

R

S

C

L

OUT

V

IN

200mV

STEP

08054-033

VS = 5V
G = +1
R

L

= 1kΩ

C

L

= 6.8pF

RS = 100Ω

08054-035

50ns/DIV50mV/DIV

OUTPUT VOLTAGE (mV)

0

100

–100

These four methods minimize the output capacitive loading effect.

• Reducing the output resistive load. This pushes the pole

further away and, therefore, improves the phase margin.

• Increasing the phase margin with higher noise gains. As

the closed-loop gain is increased, the larger phase margin
allows for large capacitive loads with less peaking.

Figure 54. 0.1 dB Gain Flatness vs. C

ADA4891-1/ADA4891-2

, VS = 5 V,

F

• Adding a parallel capacitor (C

output. This adds a zero in the closed-loop frequency
response, which tends to cancel out the pole formed by the
capacitive load and the output impedance of the amplifier.
See the Effect of R

on 0.1 dB Gain Flatness section for

F

more information.

• Placing a small value resistor (R

to isolate the load capacitor from the output stage of the
amplifier.

) with RF, from −IN to the

F

) in series with the output

S

DRIVING CAPACITIVE LOADS

A highly capacitive load reacts with the output impedance of
the amplifiers, causing a loss of phase margin and subsequent
peaking or even oscillation. The ADA4891-1/ADA4891-2 are
used to demonstrate this effect (see Figure 55 and Figure 56).

Figure 55. Closed-Loop Frequency Response, C

ADA4891-1/ADA4891-2

= 6.8 pF,

L

Figure 57 shows the effect of using a snub resistor (R

) on reducing

S

the peaking in the worst-case frequency response (gain of +1).
Using R

= 100 Ω reduces the peaking by 3 dB, with the trade-off

S

that the closed-loop gain is reduced by 0.9 dB due to attenuation
at the output. R

can be adjusted from 0 Ω to 100 Ω to maintain

S

an acceptable level of peaking and closed-loop gain, as shown in
Figure 57.

Figure 57. Closed-Loop Frequency Response with Snub Resistor, C

= 6.8 pF

L

Figure 58 shows that the transient response is also much improved
by the snub resistor (R

= 100 Ω) compared to that of Figure 56.

S

Figure 56. 200 mV Step Response, C

ADA4891-1/ADA4891-2

= 6.8 pF,

L

Rev. D | Page 17 of 24

Figure 58. 200 mV Step Response, C

= 6.8 pF, RS = 100 Ω

L

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

08054-064

–V

S

+V

S

ADA4891

08054-065

2.5kΩ

2.5kΩ

+V

S

ADA4891

>VTH or floating

Enabled

08054-086

C2

1µF

R2

50kΩ

R4

50kΩ

R3

100kΩ

C1

22µF

R1

50Ω

C6

22µF

R

L

150Ω

R

G

453Ω

R

F

453Ω

C5

22µF

ADA4891-3

+5V

V

OUT

V

IN

–V

S

C3

10µF

C4

0.01µF

+5V

TERMINATING UNUSED AMPLIFIERS

Terminating unused amplifiers in a multiamplifier package is
an important step in ensuring proper operation of the functional
amplifier. Unterminated amplifiers can oscillate and draw
excessive power. The recommended procedure for terminating
unused amplifiers is to connect any unused amplifiers in a
unity-gain configuration and to connect the noninverting input
to midsupply voltage. With symmetrical bipolar power supplies,
this means connecting the noninverting input to ground, as
shown in Figure 59.

Figure 59. Terminating Unused Amplifier with

Symmetrical Bipolar Power Supplies

In single power supply applications, a synthetic midsupply
source must be created. This can be accomplished with a simple
resistive voltage divider. Figure 60 shows the proper connection
for terminating an unused amplifier in a single-supply
configuration.

SINGLE-SUPPLY OPERATION

The ADA4891 can also be operated from a single power supply.
Figure 61 shows the ADA4891-3 configured as a single 5 V
supply video driver.

• The input signal is ac-coupled into the amplifier via

Capacitor C1.

• Resistor R2 and Resistor R4 establish the input midsupply

reference for the amplifier.

• Capacitor C5 prevents constant current from being drawn

through the gain set resistor (R
at dc to provide unity gain to the input midsupply voltage,
thereby establishing the output voltage at midsupply.

• Capacitor C6 is the output coupling capacitor.

The large-signal frequency response obtained with single­supply operation is identical to the bipolar supply operation
(Figure 18 shows the large-signal frequency response).

Four pairs of low frequency poles are formed by R2/2 and C2,
R3 and C1, R

and C5, and RL and C6. With this configuration,

G

the −3 dB cutoff frequency at low frequency is 12 Hz. The
values of C1, C2, C5, and C6 can be adjusted to change the low
frequency −3 dB cutoff point to suit individual design needs.

For more information about single-supply operation of op amps,
see the Analog Dialogue article “Avoiding Op Amp Instability
Problems in Single-Supply Applications” (Vol u me 35, Number 2)
at www.analog.com.

) and enables the ADA4891-3

G

DISABLE FEATURE (ADA4891-3 ONLY)

The ADA4891-3 includes a power-down feature that can be
used to save power when an amplifier is not in use. When an
amplifier is powered down, its output goes to a high impedance
state. The output impedance decreases as frequency increases;
this effect can be observed in Figure 34. With the power-down
function, a forward isolation of −40 dB can be achieved at
50 MHz. Figure 46 shows the forward isolation vs. frequency
data. The power-down feature is asserted by pulling the
PD2

Tabl e 7 summarizes the operation of the power-down feature.

Table 7. Disable Function

Power-Down Pin Connection (

<VTH Disabled

Figure 60. Terminating Unused Amplifier with Single Power Supply

PD3

, or

pi n low.

PDx

)

Amplifier Status

PD1

,

Rev. D | Page 18 of 24

Figure 61. Single-Supply Video Driver Schematic

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

R2

47Ω

V

IN

R3

125Ω

R6

6.8Ω

+5V

R7

68.1Ω

R1

C1

51pF

C3

15pF

C4
1nF

R4

1kΩ

R5
1kΩ

R8
75Ω

V

OUT

C2

51pF

08054-062

–39

–36

–33

–30

–27

–24

–21

–18

–15

–12

–9

–6

–3

0

0.03 0.1 1 10 100

MAGNITUDE ( dB)

FREQUENCY (MHz)

08054-059

49.9Ω

453Ω

+2.5V

–2.5V

+2.5V

–2.5V

49.9Ω

49.9Ω

49.9Ω

1V p-p
3MHz

2V p-p
1MHz

V

OUT

SELECT

HCO4

453Ω

453Ω

10µF

0.1µF

10µF

0.1µF

49.9Ω

453Ω

10µF

0.1µF

10µF

0.1µF

08054-087

ADA4891-3

ADA4891-3

1µs/DIV

1V/DIV

1µs/DIV5V/DIV

SELECT

OUTPUT

08054-088

VIDEO RECONSTRUCTION FILTER

A common application for active filters is at the output of video
digital-to-analog converters (DACs)/encoders. The filter, or more
appropriately, the video reconstruction filter, is used at the output
of a video DAC/encoder to eliminate the multiple images that
are created during the sampling process within the DAC. For
portable video applications, the ADA4891 is an ideal choice due
to its lower power requirements and high performance.

For active filters, a good rule of thumb is that the −3 dB band­width of the amplifiers be at least 10 times higher than the corner
frequency of the filter. This ensures that no initial roll-off is
introduced by the amplifier and that the pass band is flat until
the cutoff frequency.

An example of a 15 MHz, 3-pole, Sallen-Ke y, l ow -pass video
reconstruction filter is shown in Figure 62. This circuit features
a gain of +2, a 0.1 dB bandwidth of 7.3 MHz, and over 17 dB
attenuation at 29.7 MHz (see Figure 63). The filter has three
poles: two poles are active, with a third passive pole (R6 and C4)
placed at the output. C3 improves the filter roll-off. R6, R7, and
R8 make up the video load of 150 Ω. Components R6, C4, R7,
R8, and the input termination of the network analyzer form a
6 dB attenuator; therefore, the reference level is roughly 0 dB,
as shown in Figure 63.

MULTIPLEXER

The ADA4891-3 has a disable pin used to power down the
amplifier to save power or to create a mux circuit. If two or
more ADA4891-3 outputs are connected together and only one
output is enabled, then only the signal of the enabled amplifier
appears at the output. This configuration is used to select from
various input signal sources. Additionally, the same input signal
is applied to different gain stages, or differently tuned filters, to
make a gain-step amplifier or a selectable frequency amplifier.

Figure 64 shows a schematic of two ADA4891-3 devices used
to create a mux that selects between two inputs. One input is a
1 V p-p, 3 MHz sine wave; the other input is a 2 V p-p, 1 MHz
sine wave.

Figure 62. 15 MHz Video Reconstruction Filter Schematic

Figure 63. Video Reconstruction Filter Frequency Performance

Figure 64. Two-to-One Multiplexer Using Two ADA4861-3 Devices

The select signal and the output waveforms for this circuit are
shown in Figure 65.

Figure 65. ADA4861-3 Mux Output

Rev. D | Page 19 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

LAYOUT, GROUNDING, AND BYPASSING

POWER SUPPLY BYPASSING

Power supply pins are additional op amp inputs, and care must
be taken so that a noise-free, stable dc voltage is applied. The
purpose of bypass capacitors is to create a low impedance path
from the supply to ground over a range of frequencies, thereby
shunting or filtering the majority of the noise to ground. Bypassing
is also critical for stability, frequency response, distortion, and
PSRR performance.

If traces are used between components and the package, chip
capacitors of 0.1 μF (X7R or NPO) are critical and should be
placed as close as possible to the amplifier package. The 0508
case size for such a capacitor is recommended because it offers
low series inductance and excellent high frequency performance.
Larger chip capacitors, such as 0.1 μF capacitors, can be shared
among a few closely spaced active components in the same
signal path. A 10 μF tantalum capacitor is less critical for high
frequency bypassing, but it provides additional bypassing for
lower frequencies.

GROUNDING

When possible, ground and power planes should be used. Ground
and power planes reduce the resistance and inductance of the
power supply feeds and ground returns. If multiple planes are
used, they should be stitched together with multiple vias. The
returns for the input, output terminations, bypass capacitors,
and R

should all be kept as close to the ADA4891 as possible.

G

Ground vias should be placed at the side or at the very end of
the component mounting pads to provide a solid ground return.
The output load ground and the bypass capacitor grounds should
be returned to a common point on the ground plane to minimize
parasitic inductance and to help improve distortion performance.

INPUT-TO-OUTPUT COUPLING

To minimize capacitive coupling between the inputs and outputs
and to avoid any positive feedback, the input and output signal
traces should not be parallel. In addition, the input traces should
not be close to each other. A minimum of 7 mils between the
two inputs is recommended.

LEAKAGE CURRENTS

In extremely low input bias current amplifier applications, stray
leakage current paths must be kept to a minimum. Any voltage
differential between the amplifier inputs and nearby traces sets
up a leakage path through the PCB. Consider a 1 V signal and
100 GΩ to ground present at the input of the amplifier. The
resultant leakage current is 10 pA; this is 5× the typical input
bias current of the amplifier. Poor PCB layout, contamination,
and the board material can create large leakage currents. Common
contaminants on boards are skin oils, moisture, solder flux, and
cleaning agents. Therefore, it is imperative that the board be
thoroughly cleaned and that the board surface be free of
contaminants to take full advantage of the low input bias
currents of the ADA4891.

To significantly reduce leakage paths, a guard ring/shield should
be used around the inputs. The guard ring circles the input pins
and is driven to the same potential as the input signal, thereby
reducing the potential difference between pins. For the guard ring
to be completely effective, it must be driven by a relatively low
impedance source and should completely surround the input
leads on all sides, above and below, using a multilayer board
(see Figure 66).

GUARD RING

INPUT AND OUTPUT CAPACITANCE

Parasitic capacitance can cause peaking and instability and,
therefore, should be minimized to ensure stable operation.

High speed amplifiers are sensitive to parasitic capacitance between
the inputs and ground. A few picofarads of capacitance reduce
the input impedance at high frequencies, in turn increasing the
gain of the amplifier and causing peaking of the frequency
response or even oscillations, if severe enough. It is recommended
that the external passive components that are connected to the
input pins be placed as close as possible to the inputs to avoid
parasitic capacitance.

In addition, the ground and power planes under the pins of
the ADA4891 should be cleared of copper to prevent parasitic
capacitance between the input and output pins to ground. This
is because a single mounting pad on a SOIC footprint can add
as much as 0.2 pF of capacitance to ground if the ground or
power plane is not cleared under the ADA4891 pins. In fact, the
ground and power planes should be kept at a distance of at least

0.05 mm from the input pins on all layers of the board.

Rev. D | Page 20 of 24

GUARD RING

INVERTING

Figure 66. Guard Ring Configurations

NONINVERTING

The 5-lead SOT-23 package for the ADA4891-1 presents a
challenge in keeping the leakage paths to a minimum. The
pin spacing is very tight, so extra care must be used when
constructing the guard ring (see Figure 67 for the recom­mended guard ring construction).

OUT

ADA4891-1

–V

S

+IN

+V

S

–IN

INVERTING

Figure 67. Guard Ring Layout, 5-Lead SOT-23

OUT

ADA4891-1

–V

S

+IN

NONINVERTI NG

+V

S

–IN

8054-067

08054-068

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES)ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLYAND ARE NOT APPROPRIATE FOR USE IN DESIGN.

COMPLIANT TO JEDEC STANDARDS MS-012-AA

012407-A

0.25 (0.0098)

0.17 (0.0067)

1.27 (0.0500)

0.40 (0.0157)

0.50 (0.0196)

0.25 (0.0099)

45°

8°
0°

1.75 (0.0688)

1.35 (0.0532)

SEATING

PLANE

0.25 (0.0098)

0.10 (0.0040)

4

1

8 5

5.00(0.1968)

4.80(0.1890)

4.00 (0.1574)

3.80 (0.1497)

1.27 (0.0500)
BSC

6.20 (0.2441)

5.80 (0.2284)

0.51 (0.0201)

0.31 (0.0122)

COPLANARITY

0.10

COMPLIANT TO JEDEC STANDARDS MO-178-AA

10°

5°
0°

SEATING
PLANE

1.90
BSC

0.95 BSC

0.60

BSC

5

1 2 3

4

3.00

2.90

2.80

3.00

2.80

2.60

1.70

1.60

1.50

1.30

1.15

0.90

0.15 MAX

0.05 MIN

1.45 MAX

0.95 MIN

0.20 MAX

0.08 MIN

0.50 MAX

0.35 MIN

0.55

0.45

0.35

11-01-2010-A

OUTLINE DIMENSIONS

Figure 68. 8-Lead Standard Small Outline Package [SOIC_N]

Narrow Body

(R-8)

Dimensions shown in millimeters and (inches)

Figure 69. 5-Lead Small Outline Transistor Package [SOT-23]

(RJ-5)

Dimensions shown in millimeters

Rev. D | Page 21 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

COMPLIANT TO JEDEC STANDARDS MO-187-AA

6°
0°

0.80

0.55

0.40

4

8

1

5

0.65 BSC

0.40

0.25

1.10 MAX

3.20

3.00

2.80

COPLANARITY

0.10

0.23

0.09

3.20

3.00

2.80

5.15

4.90

4.65

PIN 1

IDENTIFIER

15° MAX

0.95

0.85

0.75

0.15

0.05

10-07-2009-B

CONTROLLING DIMENSIONSARE IN MILLIMETERS; INCH DIM E NS IONS
(IN PARENTHESES)ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ON LY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.

COMPLIANT TO JE DE C S TANDARDS MS-012-AB

060606-A

14

8

7

1

6.20 (0.2441)

5.80 (0.2283)

4.00 (0.1575)

3.80 (0.1496)

8.75 (0.3445)

8.55 (0.3366)

1.27 (0.0500)
BSC

SEATING
PLANE

0.25 (0.0098)

0.10 (0.0039)

0.51 (0.0201)

0.31 (0.0122)

1.75 (0.0689)

1.35 (0.0531)

0.50 (0.0197)

0.25 (0.0098)

1.27 (0.0500)

0.40 (0.0157)

0.25 (0.0098)

0.17 (0.0067)

COPLANARITY

0.10

8°
0°

45°

COMPLIANT TO JEDEC STANDARDS M O-153-AB-1

061908-A

8°
0°

4.50

4.40

4.30

14

8

7

1

6.40
BSC

PIN 1

5.10

5.00

4.90

0.65 BSC

0.15

0.05

0.30

0.19

1.20
MAX

1.05

1.00

0.80

0.20

0.09

0.75

0.60

0.45

COPLANARITY

0.10

SEATING
PLANE

Figure 70. 8-Lead Mini Small Outline Package [MSOP]

(RM-8)

Dimensions shown in millimeters

Figure 71. 14-Lead Standard Small Outline Package [SOIC_N]

Narrow Body

(R-14)

Dimensions shown in millimeters and (inches)

Figure 72. 14-Lead Thin Shrink Small Outline Package [TSSOP]

(RU-14)

Dimensions shown in millimeters

Rev. D | Page 22 of 24

Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4

Model

Temperature Range

Package Description

Package Option

Branding

ADA4891-1ARZ-RL

−40°C to +125°C

8-Lead SOIC_N, 13” Tape and Reel

R-8

ADA4891-3ARZ-RL

−40°C to +125°C

14-Lead SOIC_N, 13” Tape and Reel

R-14

ADA4891-3AR-EBZ

Evaluation Board for 14-Lead SOIC_N

ORDERING GUIDE

1, 2

ADA4891-1ARZ −40°C to +125°C 8-Lead SOIC_N R-8

ADA4891-1ARZ-R7 −40°C to +125°C 8-Lead SOIC_N, 7” Tape and Reel R-8
ADA4891-1ARJZ-R7 −40°C to +125°C 5-Lead SOT-23, 7” Tape and Reel RJ-5 H1W
ADA4891-1ARJZ-RL −40°C to +125°C 5-Lead SOT-23, 13” Tape and Reel RJ-5 H1W
ADA4891-1WARJZ-R7 −40°C to +125°C 5-Lead SOT-23, 13” Tape and Reel RJ-5 H2S
ADA4891-2ARZ −40°C to +125°C 8-Lead SOIC_N R-8
ADA4891-2ARZ-RL −40°C to +125°C 8-Lead SOIC_N, 13” Tape and Reel R-8
ADA4891-2ARZ-R7 −40°C to +125°C 8-Lead SOIC_N, 7” Tape and Reel R-8
ADA4891-2ARMZ −40°C to +125°C 8-Lead MSOP RM-8 H1U
ADA4891-2ARMZ-RL −40°C to +125°C 8-Lead MSOP, 13" Tape and Reel RM-8 H1U
ADA4891-2ARMZ-R7 −40°C to +125°C 8-Lead MSOP, 7" Tape and Reel RM-8 H1U
ADA4891-2WARMZ-R7 −40°C to +125°C 8-Lead MSOP, 7" Tape and Reel RM-8 H2T
ADA4891-3ARUZ −40°C to +125°C 14-Lead TSSOP RU-14
ADA4891-3ARUZ-R7 −40°C to +125°C 14-Lead TSSOP, 7” Tape and Reel RU-14
ADA4891-3ARUZ-RL −40°C to +125°C 14-Lead TSSOP, 13” Tape and Reel RU-14
ADA4891-3ARZ −40°C to +125°C 14-Lead SOIC_N R-14
ADA4891-3ARZ-R7 −40°C to +125°C 14-Lead SOIC_N, 7” Tape and Reel R-14

ADA4891-4ARUZ −40°C to +125°C 14-Lead TSSOP RU-14
ADA4891-4ARUZ-R7 −40°C to +125°C 14-Lead TSSOP, 7” Tape and Reel RU-14
ADA4891-4ARUZ-RL −40°C to +125°C 14-Lead TSSOP, 13” Tape and Reel RU-14
ADA4891-4ARZ −40°C to +125°C 14-Lead SOIC_N R-14
ADA4891-4ARZ-R7 −40°C to +125°C 14-Lead SOIC_N, 7” Tape and Reel R-14
ADA4891-4ARZ-RL −40°C to +125°C 14-Lead SOIC_N, 13” Tape and Reel R-14
ADA4891-1AR-EBZ Evaluation Board for 8-Lead SOIC_N
ADA4891-1ARJ-EBZ Evaluation Board for 5-Lead SOT-23
ADA4891-2AR-EBZ Evaluation Board for 8-Lead SOIC_N
ADA4891-2ARM-EBZ Evaluation Board for 8-Lead MSOP

ADA4891-3ARU-EBZ Evaluation Board for 14-Lead TSSOP
ADA4891-4AR-EBZ Evaluation Board for 14-Lead SOIC_N
ADA4891-4ARU-EBZ Evaluation Board for 14-Lead TSSOP

1

Z = RoHS Compliant Part.

2

W = Qualified for Automotive Applications.

AUTOMOTIVE PRODUCTS

The ADA4891-1W and ADA4891-2W models are available with controlled manufacturing to support the quality and reliability
requirements of automotive applications. Note that these automotive models may have specifications that differ from the commercial
models; therefore, designers should review the Specifications section of this data sheet carefully. Only the automotive grade products
shown are available for use in automotive applications. Contact your local Analog Devices, Inc., account representative for specific
product ordering information and to obtain the specific Automotive Reliability reports for these models.

Rev. D | Page 23 of 24

ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet

©2010–2012 Analog Devices, Inc. All rights reserved. Trademarks and

NOTES

registered trademarks are the property of their respective owners.
D08054-0-3/12(D)

Rev. D | Page 24 of 24