Analog Devices AD8021 e Datasheet

Low Noise, High Speed Amplifier

FEATURES

Low noise

2.1 nV/√Hz input voltage noise

2.1 pA/√Hz input current noise

Custom compensation

Constant bandwidth from G = −1 to G = −10

High speed

200 MHz (G = −1)
190 MHz (G = −10)

Low power

34 mW or 6.7 mA typical for 5 V supply
Output disable feature, 1.3 mA
Low distortion

−93 dBc second harmonic, f

−108 dBc third harmonic, f

DC precision

1 mV maximum input offset voltage

0.5 µV/°C input offset voltage drift
Wide supply range, 5 V to 24 V
Low price
Small packaging

Available in SOIC-8 and MSOP-8

APPLICATIONS

ADC preamp and driver
Instrumentation preamp

Active filters
Portable instrumentation
Line receivers
Precision instruments

Ultrasound signal processing

High gain circuits

PRODUCT DESCRIPTION

The AD8021 is an exceptionally high performance, high speed
voltage feedback amplifier that can be used in 16-bit resolution
systems. It is designed to have both low voltage and low current
noise (2.1 nV/√Hz typical and 2.1 pA/√Hz typical) while operating
at the lowest quiescent supply current (7 mA @ ±5 V) among
today’s high speed, low noise op amps. The AD8021 operates
over a wide range of supply voltages from 2.5 V to 12 V, as well
as from single 5 V supplies, making it ideal for high speed, low
power instruments. An output disable pin allows further
reduction of the quiescent supply current to 1.3 mA.

= 1 MHz

C

= 1 MHz

C

for 16-Bit Systems

AD8021

CONNECTION DIAGRAM

LOGIC

REFERENCE

–IN
+IN

–V

Figure 1. SOIC-8 (R-8) and MSOP-8 (RM-8)

The AD8021 allows the user to choose the gain bandwidth
product that best suits the application. With a single capacitor,
the user can compensate the AD8021 for the desired gain with
little trade-off in bandwidth. The AD8021 is a very well behaved
amplifier that settles to 0.01% in 23 ns for a 1 V step. It has a fast
overload recovery of 50 ns.

The AD8021 is stable over temperature with low input offset
voltage drift and input bias current drift, 0.5 µV/°C and 10 nA/°C,
respectively. The AD8021 is also capable of driving a 75 Ω line
with ±3 V video signals.

The AD8021 is both technically superior and priced considerably
less than comparable amps drawing much higher quiescent
current. The AD8021 is a high speed, general-purpose amplifier,
ideal for a wide variety of gain configurations, and can be used
throughout a signal processing chain and in control loops. The
AD8021 is available in both standard 8-lead SOIC and MSOP
packages in the industrial temperature range of −40°C to +85°C.

24

= 50mV p-p

V

OUT

21

G = –10, R

18

15

12

9

6

3

CLOSED-LOOP GAIN (dB)

0

–3
–6

0.1M 1G1M 10M 100M

F

R

= 100Ω, CC = 0pF

IN

G = –5, RF = 1kΩ, RG = 200Ω,
R

= 66.5Ω, CC = 1.5pF

IN

= 499Ω, RG = 249Ω,

G = –2, R

F

R

= 63.4Ω, CC = 4pF

IN

G = –1, R

= 499Ω, RG = 499Ω,

F

= 56.2Ω, CC = 7pF

R

IN

Figure 2. Small Signal Frequency Respon se

AD8021

1

2

3

4

S

= 1kΩ, RG = 100Ω,

FREQUENCY (Hz)

8

7

6

5

DISABLE
+V

S

V

OUT

C

COMP

01888-001

01888-002

Rev. E

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 rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] © 2005 Analog Devices, Inc. All rights reserved.

www.analog.com

AD8021

TABLE OF CONTENTS

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

Absolute Maximum Ratings............................................................ 7

Maximum Power Dissipation .....................................................7

ESD Caution.................................................................................. 7

Pin Configuration and Function Descriptions............................. 8

Typical Performance Characteristics............................................. 9

Test C irc uits .................................................................................17

Applications..................................................................................... 19

Using the Disable Feature ..........................................................20

REVISION HISTORY

3/05—Rev. D to Rev. E

Updated Format..................................................................Universal

Change to Figure 19 ....................................................................... 11

Change to Figure 25 ....................................................................... 12

Change to Table 7 and Table 8 ...................................................... 22

Change to Driving 16-Bit ADCs Section .................................... 22

10/03—Data Sheet Changed from Rev. C to Rev. D.

Updated format...................................................................Universal

Theory of Operation ...................................................................... 21

PCB Layout Considerations...................................................... 21

Driving 16-Bit ADCs................................................................. 22

Differential Driver...................................................................... 22

Using the AD8021 in Active Filters .........................................23

Driving Capacitive Loads.......................................................... 23

Outline Dimensions .......................................................................25

Ordering Guide .......................................................................... 25

7/03—Data Sheet Changed from Rev. B to Rev. C.

Deleted all references to evaluation board...................... Universal

Replaced Figure 2 ..............................................................................5

Updated OUTLINE DIMENSIONS ........................................... 20

2/03—Data Sheet Changed from Rev. A to Rev. B.

Edits to Evaluation Board Applications....................................... 20

Edits to Figure 17 ........................................................................... 20

6/02—Data Sheet Changed from Rev. 0 to Rev. A.

Edits to SPECIFICATIONS..............................................................2

Rev. E | Page 2 of 28

AD8021

SPECIFICATIONS

VS = ±5 V, @ TA = 25°C, RL = 1 kΩ, gain = +2, unless otherwise noted.

Table 1.

AD8021AR/AD8021ARM

Parameter Conditions

DYNAMIC PERFORMANCE

−3 dB Small Signal Bandwidth G = +1, CC = 10 pF, VO = 0.05 V p-p 355 490 MHz
G = +2, CC = 7 pF, VO = 0.05 V p-p 160 205 MHz
G = +5, CC = 2 pF, VO = 0.05 V p-p 150 185 MHz
G = +10, CC = 0 pF, VO = 0.05 V p-p 110 150 MHz
Slew Rate, 1 V Step G = +1, CC = 10 pF 95 120 V/µs
G = +2, CC = 7 pF 120 150 V/µs
G = +5, CC = 2 pF 250 300 V/µs
G = +10, CC = 0 pF 380 420 V/µs
Settling Time to 0.01% VO = 1 V step, RL = 500 Ω 23 ns
Overload Recovery (50%) ±2.5 V input step, G = +2 50 ns

DISTORTION/NOISE PERFORMANCE

f = 1 MHz

HD2 VO = 2 V p-p −93 dBc
HD3 VO = 2 V p-p −108 dBc

f = 5 MHz

HD2 VO = 2 V p-p −70 dBc

HD3 VO = 2 V p-p −80 dBc
Input Voltage Noise f = 50 kHz 2.1 2.6 nV/√Hz
Input Current Noise f = 50 kHz 2.1 pA/√Hz
Differential Gain Error NTSC, RL = 150 Ω 0.03 %
Differential Phase Error NTSC, RL = 150 Ω 0.04 Degrees

DC PERFORMANCE

Input Offset Voltage 0.4 1.0 mV
Input Offset Voltage Drift T
Input Bias Current +Input or −input 7.5 10.5 µA
Input Bias Current Drift 10 nA/°C
Input Offset Current 0.1 0.5 ±µA
Open-Loop Gain 82 86 dB

INPUT CHARACTERISTICS

Input Resistance 10 MΩ
Common-Mode Input Capacitance 1 pF
Input Common-Mode Voltage Range −4.1 to +4.6 V
Common-Mode Rejection Ratio VCM = ±4 V −86 −98 dB

OUTPUT CHARACTERISTICS

Output Voltage Swing −3.5 to +3.2 −3.8 to +3.4 V
Linear Output Current 60 mA
Short-Circuit Current 75 mA
Capacitive Load Drive for 30% Overshoot VO = 50 mV p-p/1 V p-p 15/120 pF

DISABLE CHARACTERISTICS

Off Isolation f = 10 MHz −40 dB
Turn-On Time VO = 0 V to 2 V, 50% logic to 50% output 45 ns
Turn-Off Time VO = 0 V to 2 V, 50% logic to 50% output 50 ns
DISABLE Voltage—Off/On
Enabled Leakage Current LOGIC REFERENCE = 0.4 V 70 µA

Disabled Leakage Current LOGIC REFERENCE = 0.4 V 30 µA

POWER SUPPLY

Operating Range ±2.25 ±5 ±12.0 V
Quiescent Current Output enabled 7.0 7.7 mA
Output disabled 1.3 1.6 mA
+Power Supply Rejection Ratio VCC = +4 V to +6 V, VEE = −5 V −86 −95 dB

−Power Supply Rejection Ratio VCC = +5 V, VEE = −6 V to −4 V −86 −95 dB

to T

MIN

V

DISABLE

DISABLE = 4.0 V

DISABLE = 0.4 V

0.5 µV/°C

MAX

− V

LOGIC REFERENCE

1.75/1.90 V

Min Typ Max

2 µA

33 µA

Unit

Rev. E | Page 3 of 28

AD8021

VS = ±12 V, @ TA = 25°C, RL = 1 kΩ, gain = +2, unless otherwise noted.

Table 2.

AD8021AR/AD8021ARM

Parameter Conditions

Min Typ Max

DYNAMIC PERFORMANCE

−3 dB Small Signal Bandwidth G = +1, CC = 10 pF, VO = 0.05 V p-p 520 560 MHz
G = +2, CC = 7 pF, VO = 0.05 V p-p 175 220 MHz
G = +5, CC = 2 pF, VO = 0.05 V p-p 170 200 MHz
G = +10, CC = 0 pF, VO = 0.05 V p-p 125 165 MHz
Slew Rate, 1 V Step G = +1, CC = 10 pF 105 130 V/µs
G = +2, CC = 7 pF 140 170 V/µs
G = +5, CC = 2 pF 265 340 V/µs
G = +10, CC = 0 pF 400 460 V/µs
Settling Time to 0.01% VO = 1 V step, RL = 500 Ω 21 ns
Overload Recovery (50%) ±6 V input step, G = +2 90 ns

DISTORTION/NOISE PERFORMANCE

f = 1 MHz

HD2 VO = 2 V p-p −95 dBc
HD3 VO = 2 V p-p −116 dBc

f = 5 MHz

HD2 VO = 2 V p-p −71 dBc

HD3 VO = 2 V p-p −83 dBc
Input Voltage Noise f = 50 kHz 2.1 2.6 nV/√Hz
Input Current Noise f = 50 kHz 2.1 pA/√Hz
Differential Gain Error NTSC, RL = 150 Ω 0.03 %
Differential Phase Error NTSC, RL = 150 Ω 0.04 Degrees

DC PERFORMANCE

Input Offset Voltage 0.4 1.0 mV
Input Offset Voltage Drift T

MIN

to T

0.2 µV/°C

MAX

Input Bias Current +Input or −input 8 11.3 µA
Input Bias Current Drift 10 nA/°C
Input Offset Current 0.1 0.5 ±µA
Open-Loop Gain 84 88 dB

INPUT CHARACTERISTICS

Input Resistance 10 MΩ
Common-Mode Input Capacitance 1 pF
Input Common-Mode Voltage Range −11.1 to +11.6 V
Common-Mode Rejection Ratio VCM = ±10 V −86 −96 dB

OUTPUT CHARACTERISTICS

Output Voltage Swing −10.2 to +9.8 −10.6 to +10.2 V
Linear Output Current 70 mA
Short-Circuit Current 115 mA

V

Capacitive Load Drive for 30%

= 50 mV p-p/1 V p-p 15/120 pF

O

Overshoot

DISABLE CHARACTERISTICS

Off Isolation f = 10 MHz −40 dB
Turn-On Time VO = 0 V to 2 V, 50% logic to 50% output 45 ns
Turn-Off Time VO = 0 V to 2 V, 50% logic to 50% output 50 ns
DISABLE Voltage—Off/On

DISABLE

− V

LOGIC REFERENCE

1.80/1.95 V

V

Enabled Leakage Current LOGIC REFERENCE = 0.4 V 70 µA

DISABLE = 4.0 V

2 µA

Disabled Leakage Current LOGIC REFERENCE = 0.4 V 30 µA

DISABLE = 0.4 V

33 µA

Unit

Rev. E | Page 4 of 28

AD8021

AD8021AR/AD8021ARM

Parameter Conditions

Min Typ Max

POWER SUPPLY

Operating Range ±2.25 ±5 ±12.0 V
Quiescent Current Output enabled 7.8 8.6 mA
Output disabled 1.7 2.0 mA
+Power Supply Rejection Ratio VCC = +11 V to +13 V, VEE = −12 V −86 −96 dB

−Power Supply Rejection Ratio VCC = +12 V, VEE = −13 V to −11 V −86 −100 dB

= 5 V, @ TA = 25°C, RL = 1 kΩ, gain = +2, unless otherwise noted.

V

S

Table 3.

AD8021AR/AD8021ARM

Parameter Conditions

Min Typ Max

DYNAMIC PERFORMANCE

−3 dB Small Signal Bandwidth G = +1, CC = 10 pF, VO = 0.05 V p-p 270 305 MHz
G = +2, CC = 7 pF, VO = 0.05 V p-p 155 190 MHz
G = +5, CC = 2 pF, VO = 0.05 V p-p 135 165 MHz
G = +10, CC = 0 pF, VO = 0.05 V p-p 95 130 MHz
Slew Rate, 1 V Step G = +1, CC = 10 pF 80 110 V/µs
G = +2, CC = 7 pF 110 140 V/µs
G = +5, CC = 2 pF 210 280 V/µs
G = +10, CC = 0 pF 290 390 V/µs
Settling Time to 0.01% VO = 1 V step, RL = 500 Ω 28 ns
Overload Recovery (50%) 0 V to 2.5 V input step, G = +2 40 ns

DISTORTION/NOISE PERFORMANCE

f = 1 MHz

HD2 VO = 2 V p-p −84 dBc
HD3 VO = 2 V p-p −91 dBc

f = 5 MHz

HD2 VO = 2 V p-p −68 dBc

HD3 VO = 2 V p-p −81 dBc
Input Voltage Noise f = 50 kHz 2.1 2.6 nV/√Hz
Input Current Noise f = 50 kHz 2.1 pA/√Hz

DC PERFORMANCE

Input Offset Voltage 0.4 1.0 mV
Input Offset Voltage Drift T

MIN

to T

0.8 µV/°C

MAX

Input Bias Current +Input or −input 7.5 10.3 µA
Input Bias Current Drift 10 nA/°C
Input Offset Current 0.1 0.5 ±µA
Open-Loop Gain 72 76 dB

INPUT CHARACTERISTICS

Input Resistance 10 MΩ
Common-Mode Input Capacitance 1 pF
Input Common-Mode Voltage Range 0.9 to 4.6 V
Common-Mode Rejection Ratio 1.5 V to 3.5 V −84 −98 dB

OUTPUT CHARACTERISTICS

Output Voltage Swing 1.25 to 3.38 1.10 to 3.60 V
Linear Output Current 30 mA
Short-Circuit Current 50 mA
Capacitive Load Drive for 30% Overshoot VO = 50 mV p-p/1 V p-p 10/120 pF

Unit

Unit

Rev. E | Page 5 of 28

AD8021

AD8021AR/AD8021ARM

Parameter Conditions

DISABLE CHARACTERISTICS

Off Isolation f = 10 MHz −40 dB
Turn-On Time VO = 0 V to 1 V, 50% logic to 50% output 45 ns
Turn-Off Time VO = 0 V to 1 V, 50% logic to 50% output 50 ns

V

DISABLE Voltage—Off/On

DISABLE

− V

LOGIC REFERENCE

Enabled Leakage Current LOGIC REFERENCE = 0.4 V 70 µA

DISABLE = 4.0 V

Disabled Leakage Current LOGIC REFERENCE = 0.4 V 30 µA

DISABLE = 0.4 V

POWER SUPPLY

Operating Range ±2.25 ±5 ±12.0 V
Quiescent Current Output enabled 6.7 7.5 mA
Output disabled 1.2 1.5 mA
+Power Supply Rejection Ratio VCC = 4.5 V to 5.5 V, VEE = 0 V −74 −82 dB

−Power Supply Rejection Ratio VCC = +5 V, VEE = −0.5 V to +0.5 V −76 −84 dB

Min Typ Max

1.55/1.70 V

2 µA

33 µA

Unit

Rev. E | Page 6 of 28

AD8021

ABSOLUTE MAXIMUM RATINGS

Table 4.

Parameter Rating

Supply Voltage 26.4 V
Power Dissipation

Observed power derating

curves
Input Voltage (Common-Mode) ±VS ± 1 V
Differential Input Voltage

1

±0.8 V
Differential Input Current ±10 mA
Output Short-Circuit Duration

Observed power derating

curves
Storage Temperature −65°C to +125°C
Operating Temperature Range −40°C to +85°C
Lead Temperature Range

(Soldering, 10 sec) 300°C

1

The AD8021 inputs are protected by diodes. Current-limiting resistors are

not used in order to preserve the low noise. If a differential input exceeds
±0.8 V, the input current should be limited to ±10 mA.

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

2.0

The maximum power that can be safely dissipated by the
AD8021 is limited by the associated rise in junction tempera­ture. The maximum safe junction temperature for plastic

1.5

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.

1.0

8-LEAD MSOP

0.5

MAXIMUM POWER DISSIPATION (mW)

While the AD8021 is internally short-circuit protected, this may
not be sufficient to guarantee that the maximum junction tem­perature (150°C) is not exceeded under all conditions. To ensure
proper operation, it is necessary to observe the maximum

0.01
–55 –45 –35 –25 –15 –5 5 15 25 35 45 55 65

Figure 3. Maximum Power Dissipation vs. Temperature

AMBIENT TEMPERATURE (°C)

power derating curves.

1

Specification is for device in free air: 8-lead SOIC: θJA = 125°C/W; 8-lead

MSOP: θ

= 145°C/W

JA

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate
on the human body and test equipment and can discharge without detection. Although this product
features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to
high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid
performance degradation or loss of functionality.

8-LEAD SOIC

01888-004

5

8

75

1

Rev. E | Page 7 of 28

AD8021

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

LOGIC

REFERENCE

–IN
+IN

–V

AD8021

1

2

3

4

S

8

7

6

5

DISABLE
+V

S

V

OUT

C

COMP

01888-003

Figure 4. Pin Configuration

Table 5. Function Descriptions

Pin No. Mnemonic Description

1 LOGIC REFERENCE Reference for Pin 81 Voltage Level. Connect to logic low supply.
2 −IN Inverting Input.
3 +IN Noninverting Input.
4 −V
5 C
6 V

S

Compensation Capacitor. Tie to −VS. (See the Applications section for value.)

COMP

Output.

OUT

Negative Supply Voltage.

7 +VS Positive Supply Voltage.
8

1

When Pin 8 (

Pin 1, the part is disabled. (See the tables for exact disable and enable voltage levels.) If the disable feature is not going to be used, Pin 8 can be tied to

or a logic high source, and Pin 1 can be tied to ground or logic low. Alternatively, if Pin 1 and Pin 8 are not connected, the part will be in an enabled state.

+V

S

DISABLE

) is higher than Pin 1 (LOGIC REFERENCE) by approximately 2 V or more, the part is enabled. When Pin 8 is brought down to within about 1.5 V of

DISABLE

Specifications

Disable, Active Low

1

.

Rev. E | Page 8 of 28

AD8021

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, VS = ±5 V, RL = 1 kΩ, G = +2, RF = RG = 499 Ω, RS = 49.9 Ω, RO = 976 Ω, RD = 53.6 Ω, CC = 7 pF, CL = 0, CF = 0, V
frequency = 1 MHz, unless otherwise noted.

24

G = 10, R

21

18

15

12

9

6

3

CLOSED-LOOP GAIN (dB)

0

–3
–6

0.1M 1G1M 10M 100M

= 1kΩ, RG = 110Ω, CC = 0pF

F

= 1kΩ, RG = 249Ω, CC = 2pF

G = 5, R

F

= RG = 499Ω, CC = 7pF

G = 2, R

F

G = 1, RF = 75Ω, CC = 10pF

FREQUENCY (Hz)

Figure 5. Small Signal Frequency Respon se vs. Frequenc y and Gain,

= 50 mV p-p, Noninverting. See Figure 48.

V

OUT

01888-005

9

G = 2

8

7

6

5

4

GAIN (dB)

3

2

1

0

–1

10M 100M

FREQUENCY (Hz)

VS = ±2.5V

±5V

VS = ±2.5V

Figure 8. Small Signal Frequency Respon se vs. Frequenc y and Sup ply,

= 50 mV p-p, Noninverting. See Figure 48.

V

OUT

= 2 V p-p,

OUT

±12V

1G1M

01888-008

24

21

G = –10, RF = 1kΩ, RG = 100Ω,

18

R

= 100Ω, CC = 0pF

IN

15

G = –5, R

= 1kΩ, RG = 200Ω,

12

9

GAIN (dB)

6

3

0

–3
–6

0.1M 1G1M 10M 100M

F

R

= 66.5Ω, CC = 1.5pF

IN

= 499Ω, RG = 249Ω,

G = –2, R

F

R

= 63.4Ω, CC = 4pF

IN

= 499Ω, RG = 499Ω,

G = –1, R

F

R

= 56.2Ω, CC = 7pF

IN

FREQUENCY (Hz)

01888-006

Figure 6. Small Signal Frequency Respon se vs. Frequenc y and

Gain, V

9

G = 2

8

7

6

5

4

GAIN (dB)

3

2

1

0

–1

0.1M 1G1M

= 50 mV p-p Inverting. See Figure 48.

OUT

7pF

9pF

7pF

9pF

10M 100M

FREQUENCY (Hz)

C

= 5pF

C

01888-007

Figure 7. Small Signal Frequency Response vs. Frequency and Compensation

Capacitor, V

= 50 mV p-p. See Figure 48.

OUT

3

G = –1

2

1

0

–1

–2

GAIN (dB)

–3

–4

–5

–6
–7

10M 100M

FREQUENCY (Hz)

VS = ±2.5V

VS = ±12V

VS = ±2.5V

±5V

01888-009

1G1M

Figure 9. Small Signal Frequency Respon se vs. Frequenc y and Sup ply,

V

= 50 mV p-p, Inverting. See Figure 50.

OUT

9

G = 2

8

7

6

5

4

GAIN (dB)

3

2

1

0

–1

V

= 4V p-p

OUT

10M 100M

Figure 10. Frequency Response vs. Fre quency and V

V

= 0.1V AND 50mV p-p

OUT

1V p-p

FREQUENCY (Hz)

, Noninverting.

OUT

01888-010

1G1M

See Figure 48.

Rev. E | Page 9 of 28