Low Noise, High Speed Amplifier
for 16-Bit Systems
AD8021
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
C
= 1 MHz
−108 dBc third harmonic, f
C
= 1 MHz
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
CONNECTION DIAGRAM
LOGIC
1
REFERENCE
–IN
2
+IN
3
–V
S
4
AD8021
8
7
6
5
DISABLE
+V
S
V
OUT
C
COMP
01888-001
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 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.
APPLICATIONS
ADC preamps and drivers
Instrumentation preamps
Active filters
Portable instrumentation
Line receivers
Precision instruments
Ultrasound signal processing
High gain circuits
24
21
18
CLOSED-LOOP GAIN (dB)
V
OUT
= 50mV p-p
G = –10, R
F
= 1kΩ, R
G
= 100Ω,
R
IN
= 100Ω, C
C
= 0pF
G = –5, R
F
= 1kΩ, R
G
= 200Ω,
R
IN
= 66.5Ω, C
C
= 1.5pF
GENERAL 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 ±2.25 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.
15
12
9
6
3
0
–3
–6
0.1M
G = –2, R
F
= 499Ω, R
G
= 249Ω,
R
IN
= 63.4Ω, C
C
= 4pF
G = –1, R
F
= 499Ω, R
G
= 499Ω,
R
IN
= 56.2Ω, C
C
= 7pF
1M
10M
FREQUENCY (Hz)
100M
1G
Figure 2. Small Signal Frequency Response
Rev. F
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: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.
01888-002
IMPORTANT LINKS for the
AD8021*
Last content update 08/17/2013 12:08 pm
PARAMETRIC SELECTION TABLES
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DOCUMENTATION
Low Power Continuous Wave (CW) Doppler for Portable Ultrasound
Systems
AN-649:
Using the Analog Devices Active Filter Design Tool
AN-357:
Operational Integrators
AN-581:
Biasing and Decoupling Op Amps in Single Supply
Applications
AN-358:
Noise and Operational Amplifier Circuits
AN-356:
User’s Guide to Applying and Measuring Operational
Amplifier Specifications
AN-402:
Replacing Output Clamping Op Amps with Input Clamping
Amps
AN-417:
Fast Rail-to-Rail Operational Amplifiers Ease Design
Constraints in Low Voltage High Speed Systems
AN-257:
Careful Design Tames High Speed Op Amps
AN-253:
Find Op Amp Noise with Spreadsheet
AN-202:
An IC Amplifier User’s Guide to Decoupling, Grounding, and
Making Things Go Right for a Change
CN-0260:
Oversampled SAR ADC with PGA Achieving Greater Than
125 dB Dynamic Range
CN-0042:
Driving the AD7366/AD7367 Bipolar SAR ADC in Low-
Distortion DC-Coupled
MT-060:
Choosing Between Voltage Feedback and Current Feedback
Op Amps
MT-059:
Compensating for the Effects of Input Capacitance on VFB
and CFB Op Amps Used in Current-to-Voltage Converters
MT-058:
Effects of Feedback Capacitance on VFB and CFB Op Amps
MT-056:
High Speed Voltage Feedback Op Amps
MT-053:
Op Amp Distortion: HD, THD, THD + N, IMD, SFDR, MTPR
MT-052:
Op Amp Noise Figure: Don’t Be Mislead
MT-050:
Op Amp Total Output Noise Calculations for Second-Order
System
MT-049:
Op Amp Total Output Noise Calculations for Single-Pole
System
MT-047:
Op Amp Noise
MT-033:
Voltage Feedback Op Amp Gain and Bandwidth
View the
AD8021 Product Page
for more documentation
EVALUATION KITS & SYMBOLS & FOOTPRINTS
View the Evaluation Boards and Kits page for documentation and
purchasing
Symbols and Footprints
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Submit your support request here:
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Quality and Reliability
Lead(Pb)-Free Data
SAMPLE & BUY
PRODUCT RECOMMENDATIONS & REFERENCE DESIGNS
CN-0260:
Oversampled SAR ADC with PGA Achieving Greater Than
125 dB Dynamic Range
CN-0042:
Driving the AD7366/AD7367 Bipolar SAR ADC in Low-
Distortion DC-Coupled
AD8021
View Price & Packaging
Request Evaluation Board
Request Samples Check Inventory & Purchase
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AD8021
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
General Description ......................................................................... 1
Connection Diagram ....................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 7
Maximum Power Dissipation ..................................................... 7
ESD Caution.................................................................................. 7
Pin Configuration and Function Descriptions............................. 8
Typical Performance Characteristics ............................................. 9
Test Circuits................................................................................. 17
Applications..................................................................................... 19
Using the Disable Feature.......................................................... 20
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
REVISION HISTORY
5/06—Rev. E to Rev. F
Updated Format..................................................................Universal
Changes to General Description .................................................... 1
Changes to Figure 3.......................................................................... 7
Changes to Figure 60...................................................................... 19
Changes to Table 9.......................................................................... 23
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—Rev. C to Rev. D
Updated Format..................................................................Universal
7/03—Rev. B to Rev. C
Deleted All References to Evaluation Board...................Universal
Replaced Figure 2 ..............................................................................5
Updated Outline Dimensions....................................................... 20
2/03—Rev. A to Rev. B
Edits to Evaluation Board Applications....................................... 20
Edits to Figure 17 ........................................................................... 20
6/02—Rev. 0 to Rev. A
Edits to Specifications .......................................................................2
Rev. F | Page 2 of 28
AD8021
SPECIFICATIONS
V
S
= ±5 V, @ T
A
= 25°C, R
L
= 1 kΩ, gain = +2, unless otherwise noted.
Table 1.
Parameter
DYNAMIC PERFORMANCE
−3 dB Small Signal Bandwidth
Conditions
G = +1, C
C
= 10 pF, V
O
= 0.05 V p-p
G = +2, C
C
= 7 pF, V
O
= 0.05 V p-p
G = +5, C
C
= 2 pF, V
O
= 0.05 V p-p
G = +10, C
C
= 0 pF, V
O
= 0.05 V p-p
G = +1, C
C
= 10 pF
G = +2, C
C
= 7 pF
G = +5, C
C
= 2 pF
G = +10, C
C
= 0 pF
V
O
= 1 V step, R
L
= 500 Ω
±2.5 V input step, G = +2
AD8021AR/AD8021ARM
Min
Typ
Max
355
160
150
110
95
120
250
380
490
205
185
150
120
150
300
420
23
50
Unit
MHz
MHz
MHz
MHz
V/μs
V/μs
V/μs
V/μs
ns
ns
Slew Rate, 1 V Step
Settling Time to 0.01%
Overload Recovery (50%)
DISTORTION/NOISE PERFORMANCE
f = 1 MHz
HD2
HD3
f = 5 MHz
HD2
HD3
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 Bias Current Drift
Input Offset Current
Open-Loop Gain
INPUT CHARACTERISTICS
Input Resistance
Common-Mode Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
OUTPUT CHARACTERISTICS
Output Voltage Swing
Linear Output Current
Short-Circuit Current
Capacitive Load Drive for 30% Overshoot
DISABLE CHARACTERISTICS
Off Isolation
Turn-On Time
Turn-Off Time
DISABLE Voltage—Off/On
Enabled Leakage Current
V
O
= 2 V p-p
V
O
= 2 V p-p
V
O
= 2 V p-p
V
O
= 2 V p-p
f = 50 kHz
f = 50 kHz
NTSC, R
L
= 150 Ω
NTSC, R
L
= 150 Ω
−93
−108
−70
−80
2.1
2.1
0.03
0.04
0.4
0.5
7.5
10
0.1
86
10
1
−4.1 to +4.6
−98
−3.8 to +3.4
60
75
15/120
−40
45
50
1.75/1.90
70
2
dBc
dBc
dBc
dBc
nV/√Hz
pA/√Hz
%
Degrees
mV
μV/°C
μA
nA/°C
±μA
dB
MΩ
pF
V
dB
V
mA
mA
pF
dB
ns
ns
V
μA
μA
2.6
1.0
10.5
0.5
T
MIN
to T
MAX
+Input or −input
82
V
CM
= ±4 V
−86
−3.5 to +3.2
V
O
= 50 mV p-p/1 V p-p
f = 10 MHz
V
O
= 0 V to 2 V, 50% logic to 50% output
V
O
= 0 V to 2 V, 50% logic to 50% output
V
DISABLE
− V
LOGIC REFERENCE
LOGIC REFERENCE = 0.4 V
DISABLE = 4.0 V
Rev. F | Page 3 of 28
AD8021
Parameter
Disabled Leakage Current
POWER SUPPLY
Operating Range
Quiescent Current
+Power Supply Rejection Ratio
−Power Supply Rejection Ratio
Conditions
LOGIC REFERENCE = 0.4 V
DISABLE = 0.4 V
AD8021AR/AD8021ARM
Min
Typ
Max
30
33
±2.25
Output enabled
Output disabled
V
CC
= 4 V to 6 V, V
EE
= −5 V
V
CC
= 5 V, V
EE
= −6 V to −4 V
±5
7.0
1.3
−95
−95
±12.0
7.7
1.6
Unit
μA
μA
V
mA
mA
dB
dB
−86
−86
V
S
= ±12 V, @ T
A
= 25°C, R
L
= 1 kΩ, gain = +2, unless otherwise noted.
Table 2.
Parameter
DYNAMIC PERFORMANCE
−3 dB Small Signal Bandwidth
Conditions
G = +1, C
C
= 10 pF, V
O
= 0.05 V p-p
G = +2, C
C
= 7 pF, V
O
= 0.05 V p-p
G = +5, C
C
= 2 pF, V
O
= 0.05 V p-p
G = +10, C
C
= 0 pF, V
O
= 0.05 V p-p
G = +1, C
C
= 10 pF
G = +2, C
C
= 7 pF
G = +5, C
C
= 2 pF
G = +10, C
C
= 0 pF
V
O
= 1 V step, R
L
= 500 Ω
±6 V input step, G = +2
Min
520
175
170
125
105
140
265
400
AD8021AR/AD8021ARM
Typ
Max
560
220
200
165
130
170
340
460
21
90
Unit
MHz
MHz
MHz
MHz
V/μs
V/μs
V/μs
V/μs
ns
ns
Slew Rate, 1 V Step
Settling Time to 0.01%
Overload Recovery (50%)
DISTORTION/NOISE PERFORMANCE
f = 1 MHz
HD2
HD3
f = 5 MHz
HD2
HD3
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 Bias Current Drift
Input Offset Current
Open-Loop Gain
INPUT CHARACTERISTICS
Input Resistance
Common-Mode Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
V
O
= 2 V p-p
V
O
= 2 V p-p
V
O
= 2 V p-p
V
O
= 2 V p-p
f = 50 kHz
f = 50 kHz
NTSC, R
L
= 150 Ω
NTSC, R
L
= 150 Ω
−95
−116
−71
−83
2.1
2.1
0.03
0.04
0.4
0.2
8
10
0.1
88
10
1
−11.1 to +11.6
−96
dBc
dBc
dBc
dBc
nV/√Hz
pA/√Hz
%
Degrees
mV
μV/°C
μA
nA/°C
±μA
dB
MΩ
pF
V
dB
2.6
1.0
11.3
0.5
T
MIN
to T
MAX
+Input or −input
84
V
CM
= ±10 V
−86
Rev. F | Page 4 of 28
